Pawn of the Pumice Castle

Field photo Set #3

2011-06-30T09:33:00.000-07:00

The newest pair of field photos are quite local to me, as they are a slice of glaciomarine layer cake left over from the last waxing of the Cordilleran ice sheet, specifically the Wisconsonian. The following pair show exposures of a glaciomarine clay unit sandwiched in-between granite bodies and Holocene soil & sediment, found within North Vancouver's uplands. What you'll see are portions of the Capilano Sediments member of the Sumas Drift group formed in the Quaternary.

The first photo (at right) is a classic exposure within the Capilano Canyon park & suspension bridge (49° 21.470'N 123° 06.698'W). You'll notice the beige coloring of clay that is packed into mud; this unit is quite distinct from surrounding Holocene soil, the greenery, and the granodiorite bedrock. It has a very smooth consistency, and upon scrutiny has micro-level faults from minor stresses placed on it. The layer dips a good 10-12º to the SE, with a NE-SW strike.

The foliage around the site is quite dense, even in the winter. Biomass detritus litters the photo, which was taken in the late winter months. This Pleistocene marine clay was formed at the front of valley glacier lobes stemming from the Cordilleran ice sheet. The continental slope at the front was relatively high, so deep sea marine deposition was not dozens of kilometers from the glacial terminus, but rather a few kilometers. Post-Pleistocene isostatic rebound was quick in the region, and it elevated this layer to at least 50m asl, and in some areas up to a few hundred meters. Post Eocene tectonic uplift of the coast mountains caused the northern edge of these types of sedimentary units to be gently warped upwards to the north and draped over the lower slopes of the older rocks of the north shore mountains.

This exposure of the same member is found along the Lynn Peak trail (49° 21.735'N 123° 01.519'W), about a quarter of the way up, roughly 300m asl. This portion is mantled by Holocene soil, and surrounded by a lot of till and colluvium. This particular photo shows the most distinct boundary surface between the clay and surrounding members. It is likely a lens of material formed during episodic activity (see link on Surficial and Bedrock geology). The continuity of the glaciomarine member is hard to follow along the north shore, as it is buried under steepland sediments, landslide debris, and thick vegetation. So spotting a slice of the cake is considered good luck for intrepid geological explorers.

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Accretionary Wedge #35: No Jive, it's Ogive

2011-06-25T21:12:00.000-07:00

Gilkey glacier ogives, rimmed by medial moraines
(58° 49.280'N 134° 21.481'W)

Evelyn over at Georneys is hosting AW #35, and the bloggers of the geoblogosphere are submitting their favorite geology words. Coming up with a favorite geoscience word was tough. I thought of going for the comically crude, but none would have been my favorite. So I went from experience and what pops into my head first. On the rare occasion I've ventured across the top of a glacier, and when doing so my companions and I always played a game of 'spot the feature'. You had to get right the specific type of crevasse or moraine, and there were no points for pointing out firn or glacial ice. My greatest success at spotting a feature was straight off the chopper at the Gilkey trench in the Juneau Icefield. The Gilkey glacier had these strange alternating bands of light and dark crescents pointing westwards towards Berner's Bay. "Ogives!"

So what are these patterns on the surface of valley glaciers, and how do they form? Ogives are curved bands across the surface of a glacier, with convexity facing downhill. The bands are characterized by alternating dark and light groupings. The darker bands are devoid of ice-bubbles, are formed from melting & refreezing of ice in the summertime, and contain sediment accumulated at icefalls where open crevasses become a pit of deposition. The lighter bands are filled with snow & air bubbles from the non-summer months when precipitation is greatest, and a fresh snowpack acts as a layer of protection against weathering. Thus ogives are a seasonally created phenomenon. The crescent shape is due to velocity/friction differences between the lateral edges of a glacier where velocity is low & friction is high, and the center of a glacier where velocity is high & friction is low.

glacial flow lines relative to surrounding bedrock

Due to their darker color, the summer bands have greater conductivity to solar radiation, and thus are topographically lower due to increased melting. My experience traversing the Gilkey glacier was that the trough created is noticeable but pretty minimal, on the order of a 8-10 foot amplitude between a dark bands trough and a light bands crest. Interestingly, the combined width of one light + one dark band corresponds to the distance a glacier traveled in a year, thus it is a proxy element of glacial motion that can give a decent measurement of an advancing glaciers speed.

During summer, the glacier's surface melts and crevasses collect windblown particles, creating the dark band
During winter, the surface is covered with snow, protecting it from weathering and creating the light band

There you have it. Ogives! A wonderful pattern seen in some of natures freezers. The Vaughn icefall in the Juneau Icefield is as close to an idealized conveyor belt of the banded pattern you can get, but there are others. Soon I plan to visit Mt. Rainier, whose alpine glaciers are purported to have some of their own ogives.

A valley glacier replete with ogive banding, stemming from near Mont Blanc in the Graian Alps

(Credit goes to Sue Ferguson for the title of this post, an homage to her excellent guide book "Glaciers of North America: A field guide")

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Kata Tjuta - the forgotten sibling

2011-06-20T08:54:00.000-07:00

Kata Tjuta, Anangu for "many heads"

Uluru is a sandstone gem of Australia's interior landscape. It rises off the plain as a formidable inselberg of rusty red solitude. It's what comes to mind about the Australian countryside for many non-Australians, whether as the Anangu name or the anglicized 'Ayers Rock'. Savvy geologists, physiographers, and locals, however, will know about the lesser known gem of conglomerate rock domes not 30 kilometers to the west of Uluru. The Olgas, known as Kata Tjuta in the Anangu language, are a collection of 36 conglomerate rock domes rising off the plain to various heights. The highest is Mount Olga, with a prominence of 546m.

Basic stratigraphic cross-section of
Uluru and Kata Tjuta

Kata Tjuta is part of the same stratigraphic formation as Uluru (see diagram at right), a unit of arkosic sandstone derived from Cambrian alluvial fan deposits of sediment that were buried and lithified over deep time. The difference in shape & topography between the two is due to the structurally weaker conglomerate of the Olgas (the Mount Currie Conglomerate) being exploited by folding, faulting, and subsequent hydrologic weathering & erosion. The conglomerate matrix is comprised of granodiorite, basalt, gneiss, and fine sand as the cementing material. Essentially, Uluru is the tougher end of the layer, though it does not lack features created from weathering such as pits and tafoni-based honeycomb surfaces (indicative of Mediterranean paleoclimates). Even though the conglomerate lithology of Kata Tjuta lacks the feldspar mineral content that Uluru has, fractured blocks were exploited, making the initial mass structurally weaker, even though it is mineralogically stronger. Both ends started out as a large singular massive block, but Cenozoic Australian climates have taken a greater toll on the Olgas for the reasons stated.

Back in the Neoproterozoic, the Petermann mountain range was more formidable than it is today, due in major part to the Petermann orogeny. However, the Neoproterozoic/early Paleozoic climate was more temperate, so its peaks were being denuded by precipitation at a greater rate than the more subdued Holocene landscape is by current aeolian forces. Alluvial fans were created along the flanks of the Petermann foothills, each differing slightly in lithology, but not in origin. These fans formed a piedmont range that was a major part of Petermann foreland basins, such as the Amadeus, Georgina, Ngalia, and Officer basins of then central Australia. The fan material developed sequentially into flysch once a eustatic change in sea level occurred in the late Cambrian, covering the region in a shallow sea. Continuing weight of added sediment + the weight of the increasingly deepening sea was enough pressure to lithify the alluvial fans/flysch into arkosic sandstone (Uluru) & conglomerate (Kata Tjuta), each portion representing a different fan thus a slightly different lithology, all connected together during the melding of adjacent sedimentary units. If we could remove the overburden of sand & schist members, we likely could find the area where the conglomerate and sandstone grade into each other.

Google Earth snapshot of Central Australian plain, with Kata Tjuta @ left and Uluru @ right (VE = 3x)
Coordinates for centerpoint = 25° 18.710'S 130° 53.730'E

Australia was quite geomorphically active during the Paleozoic; a contrast to the quiet old continent of today where relief and rates of denudation are comparatively low, and atmospheric hazards dominate. After the transgression of the early Paleozoic, the sea receded and orogenic activity took over in the Devonian, thrusting and folding and faulting Central Australia, to the point that the Mount Currie Conglomerate formation folded with surrounding units into a distinct syncline. The Late Paleozoic – Mesozoic – Tertiary periods began a slow march of weathering & erosion of overburden, until the exposure of the ends of the Mount Currie Conglomerate finally revealed a more resistant rock. Exposure to the atmosphere is estimated to have occurred during the Jurassic. A basin between Uluru and Kata Tjuta collected aeolian sands and dunes throughout the Quaternary, thus planing the region through depositional mechanisms. All that stood out in the plain were the tips of rocks derived from a resistant lithology. The rock domes of Kata Tjuta specifically dip 10-20º with a SW-NE strike.

The finer features of the Olgas have been primarily shaped by precipitation during more temperate paleoclimatic conditions. Freeze-thaw processes acted on joints in the rock, fracturing the surface. Rivulets of creeks and small waterfalls promoted the formation of potholes and gorges. Since granite is a primary ingredient in the Kata Tjuta Mount Currie conglomerate, spheroidal weathering was able to smooth and accentuate a rounded dome shape to the remaining 36 mini-bornhardts by working on the angles & corners. Of course, iron content exposed to the atmosphere colored the veneer of Kata Tjuta to that typical iron oxide rusty-red. Some visible structures noticeable when perusing the rocks include limited tafoni structures among the rock domes. Slickensides are also apparent, indicating displacement of large sheets of the conglomerate during times of acute mass wasting.

As an aside, I stumbled upon an interesting take on the formation of Kata Tjuta when google-searching: Tas Walker's Noachian interpretation of Kata Tjuta. It is a prime example of working backwards with the scientific method, where a proposed theory is the starting point, and evidence to support it is anecdotally surmised to fit that theory. Remember, if a null hypothesis cannot be rejected, and credibility cannot be established through peer review, it is not science, and certainly not geomorphology science. Current [accredited] geomorphology research reveals noticeable increase in relief amplitude of both Uluru and Kata Tjuta inselbergs throughout the Cenozoic, which is atypical of the ideal cycle of erosion (see additional links). Interesting mechanisms must be at play, and a deeper look into the asthenosphere, lithospheric flexure, and the mass dynamics between the overburden and the Mount Currie Conglomerate are called for.

Thanks to my brother for the above photo of the Olgas, circa 2007

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A new toy! Can I play?

2011-06-11T09:49:00.000-07:00

I like volunteering. You meet compassionate people with similar interests & concerns in an informative setting. However, I live in the realities of a capitalist western country, so the [very] limited free time I have outside of university studies restricts my volunteerism, as it logically is the first thing to get cut during crunch time and the search for funds. Summertime is a bit different: classes are few or nonexistent, daylight is plentiful, and my general mood is happier & more energetic. Consequently, I tend to volunteer with local organizations that have environmental directives, and over the years I've found a few that have programs which are laid out in a simplistic fashion, and thus easy to volunteer portions of my free time for. One in particular I'm on my 4th year with involves canvassing residents of Langley on how to protect their dwindling groundwater supply through conservation and community action (~50% of the townships water supply is provided by unconfined or shallow-confined aquifers).

A sample of vesicular basalt as a control in an experiment. The sample was obtained from Mt. Rainier

In more recent years, with my growing interest in academic research, I've started asking university professors if they or their grad students need any field/lab assistance with their research. Any that have ongoing work always say yes, and when I come in with enthusiasm and interest in reading & discussing their work, they shoot back with an even greater level of enthusiasm. Probably the best aspect of volunteering in labs or the field is not the possibility of paid work, nor the time to pick the brains of current researchers, nor getting my foot in the door. Those are all excellent aspects, but the best has to be the exposure to the precision technology that I get to [cautiously] fiddle with and test out, and see its application towards specific facets of quantified research.

One recent new addition to the university had the petrologist professor quite giddy, and him and I got to play around with the new device for awhile, figuring out all its quirks and functions, and running some initial control tests to ensure proper functionality. The device was something I'd never heard of before, but the explanation of its logic and level of precision made perfect sense. I speak of a Helium-based pycnometer (pictured right).

It is hard to get an accurate measurement of density for vesicular rocks, such as vesicular basalt, pumice, scoria, etc... due to the irregular arrangement of void space in their matrix where gasses exsolved. Helium is a relatively inert gas, so functions better than a nitrogen/oxygen/argon mixture which could be adsorbed by silicic material. Helium is better at diffusing within rock samples of high surface area with the tiniest, micrometer-level pore spaces, ie. vesicular rocks. Thus the displacement of Helium between containers (one with the rocks and one without), and application of the ideal gas law, and we get the volume of the rock sample with deadly accuracy. We tested out the device using some vesicular basalt (pictured above) gathered from pyroclastic flows ejected from Cascade Arc volcanoes. Looking at the basalt petrographically was important as well, so I made thin sections for viewing under the microscope and we viewed the optical mineralogy of the basalt.

Mt Edziza stratovolcano, which has erupted felsic
magmas such as rhyodacite or trachyte/comendite.
Image courtesy Canadian Encyclopedia

The pycnometer is supposed to help the professor's research of the geochemistry of the Edziza volcanic complex within the NCVP. I hope to assist in as much of it until the concluding phases and journal publication, mainly because it allows further access and experience with new physical geography/geology toys. I've also recently got some fresh experience with a 15m long sediment transport flume, but that's another research tale I hope to tell after more time with the flume.

For other undergrads I strongly recommend volunteering your time & energy to your university profs and grad students. Trust me, they are likely to welcome your assistance, and you'll benefit from the experience and the contacts, especially if post-graduate studies is on your radar. It gets your foot in the door, and is thus invaluable.

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Geology at a Birthday Party

2011-06-06T09:30:00.000-07:00

My niece recently had her 10th birthday, and I felt it fitting to add to her burgeoning rock & mineral collection with some flint, chert, and serpentine. I mentioned the properties of serpentine to her, and its connection to asbestos, which is a carcinogen. She must have forgotten the part where I mentioned there is no chance of inhaling carcinogenic asbestos from the fist-sized rock I gave her unless she grinded it into a fine mist, nor does it have the mass of chrysotile needed to make her lungs even notice. But lo and behold a few hours later she had placed a paper on top of her rock box ..."Warning - Cancer rock inside".

An opportunity to educate her on the properties of minerals, and she took to it. Kids get right away that rocks are essentially a collection of minerals in different ratios. I'm amazed at how easy it is for kids to quickly grasp many things geological; Sometimes I wish I had such a malleable mind when I'm engulfed in my university studies. Specific gravity/density is a hard one to explain, but streak powder, cleavage, fracture, hardness, were all easy to demonstrate given that visual demonstration of them is straightforward. If you try this, I would recommend not using the mirror example for hardness, as some kids might run off to try it on bathroom mirrors.

Later on after her party, we sat down to watch some old Simpsons episodes on TV, and Treehouse of Horror V was what was showing. Homer invented a time machine by modifying a toaster, and it catapulted him back to what appeared to be a blend of the Paleozoic and Mesozoic eras, and even some Neogene (a Megatherium alongside a T-Rex??). His father gave him sage advice about not touching anything in the past, as doing so could alter the future in ways he couldn't possibly imagine. Homer was chased by a T-Rex, eventually escaping. Unfortunately, upon sitting down for a rest, he squashed what is considered the first land-walking animal. I speak of the Eusthenopteron:

courtesy 20th Century Fox

Homer killed the terrestrial evolutionary process! For some reason, that lead to the human race being 50-feet tall giants. Wouldn't it lead to us remaining aquatic animals?? Why am I trying to find evolutionary logic from a late-night cartoon? Meh, I was just pleased to see these archaic lifeforms I'm familiar with used for satire.

Papers I'm reading: Trends in the timing and magnitude of floods in Canada

2011-05-31T09:09:00.000-07:00

GIS map of the Atlas of Canada, showing numerous hydrometric measurement stations in the western half of the country

In case anyone hasn't noticed, Canada is huge. The country's vast area and varied topography lends itself to a multitude of different hydrological regimes, influenced atmospherically on a meso-macro scale by Polar & Tropical air masses. The warm vs cold air mass war has its battleground across the latitudes of Canada, from 42° - 66.6°N, with the only region that can be called "calm" being the ice-capped tundra islands north of the Arctic Circle. Very few places in Canada do not receive decent snowfall, so spring freshet runoff from snowpack melt is typical, and measuring it is every Canadian fluvial hydrologists nitty-gritty.

Bella Coola airport during Sept. 2010 flood
A prime example of a rainfall-induced flood

Climate change towards a warming trend must have an impact on the various hydrological regimes and how the hydrologic cycle has been altered due to that impact. As I've said, there are a multitude of different hydrological regimes, so there are likely a multitude of different trends. This line of thought brought me to an academic paper in the Journal of Hydrology that reviews trends in timing & magnitude of floods in Canada due to hydrologic shifts, and does so by looking at the established physiographic regions of Canada. Juraj Cunderlik and Taha Ouarda from the Natural Sciences and Engineering Research Council of Canada Chair on Statistical Hydrology analyzed flood data gathered from several dozen strategically placed monitoring stations throughout the hydrometric network of Canada.

This study investigates trends in the timing and magnitude of seasonal maximum flood events across Canada. A new methodology for analyzing trends in the timing of flood events is developed that takes into account the directional character and multi-modality of flood occurrences. The methodology transforms the directional series of flood occurrences into new series by defining a new location of the origin. A test of flood seasonality (multi-modality) is then applied to identify dominant flood seasons. Floods from the dominant seasons are analyzed separately by a seasonal trend analysis. The Mann–Kendall test in conjunction with the method of pre-whitening is used in the trend analysis. Over 160 streamflow records from one common observation period are analyzed in watersheds with relatively pristine and stable land-use conditions. The results show weak signals of climate variability and/or change present in the timing of floods in Canada during the last three decades. Most of the significant trends in the timing of spring snowmelt floods are negative trends (earlier flood occurrence) found in the southern part of Canada. There are no significant trends identified in the timing of fall rainfall floods. However, the significance of the fall, rainfall-dominated flood season has been increasing in several analyzed watersheds. This may indicate increasing intensity of rainfall events during the recent years. Trends in the magnitude of floods are more pronounced than the trends in the timing of floods. Almost one fifth of all the analyzed stations show significant trends in the magnitude of snowmelt floods. Most of the significant trends are negative trends, suggesting decreasing magnitudes of snowmelt floods in Canada over the last three decades. Significant negative trends are found particularly in southern Ontario, northern Saskatchewan, Alberta and British Columbia. There are no significant trends in the magnitude of rainfall floods found in the analyzed streamflow records. The results support the outcomes of previous streamflow trend studies conducted in Canada.

What did they find? (delving into the abstract's details)

The study first defines some ground rules:

Minimum of 20 years of observational data
Statistically significant flood regimes usually have bimodal seasons (spring freshet season + fall rainfall season). There were no stations identified with three or more significant flood seasons.
Watersheds used in the statistical study are characterized by relatively pristine and stable land-use conditions, with less than 5% of the watershed area being modified by human development
It is not feasible to get thorough coverage of streamflow data across Canada due to the country's sheer breadth, and inaccessibility of certain regions
The pulse day = the day for which the cumulative departure of the streamflow from the average streamflow for the year is most negative. Most acutely observed during the spring freshet season within high relief terrain

I'm not going to detail their establishment of a statistical methodology to gauge multi-modal flooding seasons, as I'm more interested in the findings about floods in the country (statistical know-how is something I'm lacking, soon to be remedied). In terms of timing trends, readings in southern Canada over the last generation are showing a trend towards earlier spring melt floods. This trend is particularly acute in southern Ontario, Alberta, and BC. Changes in freshwater ice break/freeze up spring dates are strongly linked to large-scale atmospheric and oceanic oscillations, with positive feedback mechanisms as the driving force. Only 16 stations, which is 10% of those included in the study, had a statistically significant trend in the timing of spring freshet floods during the last generation. Of those 16, 14 had a negative trend pointing to earlier occurrence. Only 2 stations had a positive trend pointing to later occurrence of spring floods, and those were in the tundra of Nunavut.

The real crux of the study is the findings about the change in flood magnitudes, as the values associated with volume/discharge are more striking than the shifts in the timing of said discharge. There is only a weak trend in having earlier melt runoffs, but a more significant trend in having a lower magnitude of those melt runoffs. The trend shows decreasing streamflow in heavily glaciated areas (ie. alpine glaciers of Rockies, valley glaciers of sub-Arctic & western Cordillera) during the typical spring runoff season for those areas of April - July. On average, the mean annual spring maximum flows have decreased by approximately 1% per year over the analyzed period of 1974 - 2003. My home province of BC had some intriguing findings: there was some significant increasing trends in spring maximum flows (increased snowmelt-induced flows) and significant decreasing trends at the beginning of summer (reduced snowmelt-induced flows); this is essentially showing that the snowpack is melting at a greater pace earlier in the season, leaving the summer months less supplied with meltwater from the snowpack. This is not a good trend as that scenario exacerbates drought conditions typical of BC in the summer, when a persistent Pacific High settles over the region. Indeed the paper finds that accompanying climate data (air temps) are shifting at a quicker-than-anticipated pace from the coldest to the warmest season, causing greater flow spikes in response.

You mentioned "bimodal". What about the fall rainfall season trends?
Almost a non-issue amongst the observed data. The authors note only a potential for increasing rainfall during the fall season, as certain regions recorded occasional above-average spikes in fall rainfall in the last decade. Further accumulation of data throughout the coming years will shed light on the significance of the rainfall floods, and trends in their timing & magnitude. I should note that not all physiographic regions in Canada that have bimodality have the second, lesser, rainfall-induced one in the autumn months. Rather, some regions, most notably the prairie provinces, have the rainfall-induced flooding in the summer months due to convective storms.

What are the take-home messages?

There are many implications for the decreasing snowpack melt, and how it interacts with certain biogeochemical cycles. Particular regions of Canada rely on the spring melt to supply freshwater, and in BC, hydroelectric power will be adversely affected by a decrease in discharge at certain expected intervals. You've likely seen the news on how floods in Manitoba have adversely impacted populations living in flood plains there, but that has more to do with latitude, topography and a South - North sloping drainage basin (Anne Jefferson at Highly Allochthonous has a great post on the topic). Ongoing changes in the timing and magnitude of spring floods are not restricted to a particular flood seasonality type, but rather occur across Canada in different climatic and hydrologic regimes. Ultimately, the paper highlights that trends in the magnitude of floods are more pronounced than trends in the timing of floods, and the changes in magnitude are having a great impact among natural systems connected to the melting of the snowpack in the spring.

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Accretionary Wedge #34: That is Weird

2011-05-23T09:01:00.000-07:00

This months Accretionary Wedge is being hosted by Dana Hunter over at En Tequila Es Verdad, which Google translates as "In Tequila is Truth" (don't ask this teetotaler what that means). The theme is any geology which the blogger considers weird. My limited experience means many geological phenomena I observe are initially head-scratchers, but subsequent investigation usually becomes a learning experience, and later I can't imagine a time before understanding the phenomenon.

In choosing what to post about that's weird, a memory popped into my head that quickly settled the issue. What better to include in this carnival on weird geology than a landform that has no unifying theory on its origin, but rather a bunch of hypotheses? What I speak of is the Mima Mounds, located 20km south of Olympia, Washington. This set of mounds is the only I have visited, but variations of Mima Mounds exist elsewhere: Lake District in Oregon, Northern China, and in the Western Sahara, to name a few. The geographic and climatic spread means that certain groups of the mounds have more explanation for their genesis, ex. the Oregon-based mounds have a more definitive volcanic morphology. But the mounds in Washington I'm focusing on continue to baffle geologists. Hypotheses about their origin range from animal construction - seismicity - periglacial kettle topography.

The mounds outside Olympia measure around 5-8 feet in height, and 12-20 feet in rough diameter. They are similar to the prairie-based pimple mounds of the southern Midwest states, and their might be connections based on pedological similarities. If you are a keen geologist, each explanation will stir up good probing questions, many of which are yet to be answered fully. For instance, the gopher proposal is criticized for lack of zoological evidence at the Washington Mima Mounds, plus their density raises questions of competition for food resources if a multitude of gophers built them, or necessity if many mounds were built by a few gophers. The earthquake hypothesis is a compelling one, and more research into the physics of the mounds' granular material should be revealing once it comes forth.

Click for larger version and read about the different hypotheses scientists have for the origin of the mounds.
Info board courtesy Washington State Department of Natural Resources

Most current research into the Mima Mound phenomena is concentrated around the periglacial hypothesis: Kettle & Kame topographical depressions (sun cups) were filled with glacial sediment during rapid retreat at the end of the last Ice Age. Repeated outburst floods as the glacial front retreated & disintegrated provided sediment that filled the depressions. Those depressions experienced subsequent freeze-thaw heave; hence they are arguably akin to small-scale pingo formations. However, glacial conditions are not apparent at several places where the mounds exist, even when examining deep-time paleogeography. Also of note is that not all mound formations have the same soil/sediment profile, even within the same mound group. Some of my own quick observations at the Mima Mounds Natural Area include how the mounds are more diversely vegetated, some mounds have a deflated appearance, and that exposures of the substrate revealed a primarily gravelly/pebbly mixture that reminded me of glacial diamicton.

Washington DNR LIDAR image of Mima Mounds (left) with matching Google Earth image (right)
Site is near Littlerock, Wa. (46° 53.273'N 123° 3.054'W)

Geology that can be considered 'weird' is refreshing to have around. A lot of it is nature's abstract art. I considered doing the tessellated pavement structure of Eaglehawk Neck in Tasmania, but that has a thorough explanation, and honestly, when thinking of strange geological formations, one's that are unexplained and/or under debate strike my fancy more. Finding out that not everything in earth science is yet definitive gives me a chance, albeit small, to be a future pioneer.

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Field photo Set #3

2011-05-17T09:27:00.001-07:00

A recent stopover in Princeton, BC gave me an opportunity to sidetrack to a couple interesting outcrops that expose sedimentary strata of different formations. It was a perfect day - clear skies, temps in the high teens, dry but not too dry - summer come early. Without even trying, on occasion I was within meters of adventurous local wildlife - a beaver, several deer, and a young black bear.

One particular exposure along the TCT, nicknamed the "Red Ochre Bluffs" because they were used by natives to create red pigment, is particularly interesting for its very reddish color, due to a high % content of the mineral haematite (iron oxide) within the bedded chert. Technically it is an outcrop of the Vermillion Bluffs shale member, part of the Allenby formation of the Eocene epoch (45-50 Ma). This is a fossiliferous member, where fossils of maple, alder, fir, pine, dawn redwood and ginko have been found, along with one of the world's oldest fossilized bees. There is a noticeable dip to the beds of about 10°, striking NNE-SSW.

At another part of Princeton, behind a small restaurant, is the only exposure in Princeton of the Summer Creek sandstone member of the Allenby formation:

A keen eye will notice the concretions, the cross laminations, and an apparent conglomerate boulder 'xenolith' that became part of the package, though it might be a beaten up granite-family rock. The sandstone layers have an approximate dip of 25°, and a strike of E-W. The member is mantled by a foot of glacial till (Princeton has a few kettle lakes of interest that showcase glacial geomorphology). This sandstone is some of the toughest I've felt; the layers are highly compacted and the presence of plenty of cementing material makes it a strong variant.

The Vermillion Bluffs exposure can be found @ 49° 26.695'N 120° 32.665'W, after a 2km walk along the TCT. Part of the walk goes through a long tunnel where you can practice your bet megalomaniacal laugh.
The Summer Creek sandstone rockface can be found @ 49° 27.313'N 120° 30.646'W, behind Billy's Family restaurant, where you can park and take a look at how First Nations hollowed out a cave within the sandstone to store plunder.

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Looking through the archives: Melbourne's climate

2011-05-13T14:23:00.000-07:00

Satellite image of pyrocumulus clouds over Victoria & New South Wales,
taken by NASA's Aqua satellite in early February 2009

The climate of Melbourne, Victoria, Australia is one of great variation relative to the rest of the continent, but still moderate as oceanic effects and broad relief limit extremes, especially in terms of freezing temperatures and excessive rainfall. The city is located at the south-central side of the state of Victoria, which is the southeast corner of Australia. With a Latitude/Longitude of 37.5°S 145.0°E, Melbourne falls within what is technically considered the mid-latitude region. In terms of global circulation patterns, the city is affected by not only mid-latitude westerlies, which brings air across the west of the continent to the city, but also by the subtropical High and the Antarctic circumpolar vortex. The subtropical High normally resides in New South Wales for most of a typical year, but during the southern hemisphere summer the ITCZ (Intertropical Convergence Zone) descends into northern Australia, thus pushing the subtropical High south into Victoria and Melbourne. These seasonally changing patterns make Melbourne a diverse region in terms of weather, and fosters extreme events such as bushfires & droughts that are amplified by El Niño southern oscillations.

Melbourne at a Glance

Melbourne lies quite flat on the horizon. A coastal city of 4 million with a secluded port as its access to the Indian Ocean (via Bass Strait), Melbourne is at the confluence of two major rivers that flow into Port Philip (Yarra and Maribyrnong). Geologically, Melbourne is mostly underlain by Silurian marine sediments, and modern alluvium from Yarra. The marine sediments were uplifted from the shallow Bass Strait. This highlights how low the general relief of southern Victoria is. With a sea level decrease of just 70m, a land bridge would form between the city and the island of Tasmania.

In terms of precipitation, this low relief makes Melbourne susceptible to flash flooding during more intense showers/thunderstorms in both La Niña and spring seasons. Poor drainage and infiltration through city streets, combined with a low greenspace ratio, exacerbate flash floods in the city.

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USGS and GIS

2011-05-09T06:45:00.000-07:00

I can't stand acronym overload, but lately I've been caught overusing them. Yesterday a discussion about construction at a park and the info they put up about ephemeral streams resulted in me using 'WRC', 'CWH' and 'BFR' to the befuddlement of my friend. But in the case of this blog, I can't imagine anyone reading it not grasping the two acronyms in this posts title.

Many of the earth science/physical geography professors and grad students I've talked to are almost unanimous in enjoying the field work aspect of their research. However, some of them are apprehensive about GIS technology, believing that increased ubiquity of the software will reduce or even eliminate the need for hard data gathering that is a big part of field work. Is that true? I don't know. I can surmise that depending on circumstances it could be, and I've certainly been to a few geomatics presentations where the crux of a new technique is to gather empirical geographic data without leaving the desk.

However, good GIS data is hard to find, and free GIS data even harder. Our own Geological Survey does not release much data to the public for free, and finding any GIS digital elevation model (DEM) files is akin to a needle-in-haystack search. So I was surprised when looking up information on Crater Lake and stumbling across USGS's collection of DEM files on the lake's bathymetry. Scratch that ... I wasn't surprised, as I've gotten used to the ridiculous restrictions my own government places on what should be freely available public information (these restrictions aren't limited to the geographic realm). One of my GIS bosses remarked on how his students are finding it really hard to collect digital data for their term projects, and he further mentioned that most projects involve analysis of geographic phenomena in BC. Even my own work projects involving examinations of local watersheds was shelved due to lack of shapefiles or anything that could be converted to such without a lifetime of eye damage.

But is the USGS stuff I found really any good? Cracking open ArcGIS to take a look at the bathymetry data, I was immediately struck with déjà vu. Where had I seen this layout of Crater Lake before? Of course, I see a variation of it in passing everyday, pinned up on my apartment wall:

At a gift shop in Crater Lake park, there was a huge 6-foot tall version of the above geologic map with even more detail. Alas, it was only for display, but the 4-foot tall version available for customers has good detail for a pretty penny.

I was able to do lots with the data, modifying it, adding annotations, creating a color scheme for entities, and segmenting portions of Crater Lake geology using primitives as splitters. Using the data in ArcGlobe was especially interesting, as you get a true sense of scale and perspective for all the features above & below lake level because you can strip away the water with a click. Some of the diagrams I've seen in Crater Lake academic papers have definitely used these DEM files. The resolution is incredible, as the 2000 bathymetric survey conducted by USGS, NPS, and University of New Hampshire's CCOM used multibeam acoustic sounders that translated data to a 2-meter-per-pixel representation factor.


The virgin view of Crater Lake in ArcGlobe [Top Left]. USGS 7.5 arcminute DEM of Crater Lake, showing shaded relief bathymetry [Top Right]. Angled perspective of 7.5 arcminute Crater Lake DEM, with annotated structures [Bottom]

Thank goodness for the USGS! Good physical geography GIS data is out there, based on surveys they've conducted, and data they digitized. Best of all, it's freely available to the public. Now if only my federal government would allow GSC to follow suit.

On the subaqueous features/structures of Crater Lake

Rhyodacite Dome = youngest (5 Ka), shallowest subaqueous feature. It is a highly silicic lava dome that has formed from a vent that intruded through both the andesitic Central Platform & the eastern flank of Wizard Island. Rhyodacitic flows and domes were common in Mazama's history between 40-5 Ka.

Central Platform = Subaerial andesite flows that experienced magma differentiation from within the primary chamber. Successive eruptions (7-6 Ka) that built up the platform were above lake level, giving the platform a low, broad relief until flows met the old shoreline.

Merriam Cone = Cinder cone whose lower portion/foundation was formed as a resurgent dome, composed of subaqueous andesite, formed from completely submarine eruptions circa 7.7-7.5 Ka. It has a nearly geometrically idealized cone shape. Peak is ~150m below current lake level. Origins and formation still not agreed upon (Resurgent dome or Cinder cone or how much of a combination??).

Phantom Ship = Oldest (400 Ka), partially subaqueous feature. Considered to be the top of a basic-andesitic volcanic dike, a remnant of a small vent that might have fed parasitic cones on pre-cataclysmic Mazama's eastern flank (see also Devil's Backbone).

Various Depositional Basins = Colluvium, volcaniclastics, volcanic breccia, and ash particles, all weathered and transported to the low-lying depressions of the caldera. The rim has plenty of talus slopes. There is a huge landslide deposit on the southern end of the lake, called the Chaski Bay landslide, with a debris avalanche volume of 0.1 km³ (couldn't find an exact date on the slide). Evidence of the slide triggering a mild tsunami is found at Cleetwood Cove on the northern end.

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Columbia Basin Trip: Day 3 - McCall and a bunch of Falls

2011-05-03T08:41:00.001-07:00

My third and final day out in Oregon included a spectacular hike through a nature preserve, and a drive along an historic highway where there is the greatest concentration of high waterfalls in the US. I lost count of how many waterfalls I saw, and recalling all their names is tough (Elowah, Oneonta, Multnomah, Horsetail, Ponytail, Latourell, Sheppard Dell, just to name a few). Each fall had its own character, in which the basalt rockfaces they flowed over varied in layering, formation, and vegetation.

Info board @ Rowena Crest parking

But first, before the falls, it was time for a satisfying hike. Hiking Oregon's Geology guide book spoke of a 4-5 mile hike through a nature preserve just outside The Dalles (which I learned is pronounced "Dals", not "Dall-ehz"). Called the "Rowena Crest/Tom McCall Preserve", most of the geology relating to this hike is distant, observed by viewing the Columbia River gorge on the opposing Washington state side. Their side has the Ortley Pinnacles, fragments of basalt cemented together at a fault line. Mounds dotting the preserve's open stretches of grassland are erosional remnants of St. Helens ash deposits; they are more subdued and more sporadic than the infamous Mima Mounds, which may or may not have the same genesis. The real highlight of the hike is ecological, as at this point in springtime I could spot lupines, balsamroot, and blossom trees, and that was with my weaker-than-novice botanical background. The whole scene was very colorful at this time of year, and was capped off with sunny, turbulent weather.

The bulk of the geology in Day 3 came in the form of neverending pullovers and short, grinding switchbacks to view a multitude of waterfalls. This collection of falls was created when the Missoula floods cut away the gentle foothills of the flood basalts, leaving the cliffs and their creeks-turned-falls. If my recollection is correct, all but two of the falls I visited were of the plunge variety (Oneonta was Step-Pool, Sheppard Dell was tiered/fan). Discharge was excellent, fueled by mid-spring rains and freshet melt from peaks ranging from 1200-1600m elevation (see above cross-section).

Two particular falls were a real treat to behold: Multnomah & Latourell. The former is the highest in Oregon, second highest in the continental US, and technically is a hybrid of plunge/step-pool, with a higher and lower set of falls. Differential cooling rates of the various Columbia flood basalt lava flows (Grande Ronde Basalt) provided Multnomah with distinctive layering from top-bottom. I could make out entablature basalt layers (fast cooling, fractured into irregular blocks & joints), a pillow basalt layer (fastest cooling when exposed to water, forming rounded cobbles), and columnar basalt layers (slower cooling under entablature, forming slender hexagonal blocks) at the very top and interspersed near the bottom behind the rockfall scarp. Multnomah Falls splashwater erodes softer layers of rock below & behind the falls, creating a plunge poll and amphitheater semi-cave. The higher falls recede upstream faster than the lower falls due to weaknesses in their lowest basalt layers. Large pieces of basalt rockface have historically been calved off, including a 400 ton piece falling into the plunge pool and drenching a wedding party 15 years ago.

"... Observations of waterfalls over Columbia River basalt have shown that falls often occur where flows are flat lying or dipping upstream. This condition allows blocks produced by vertical joints to remain stable until support is withdrawn by erosion of softer interflow material at the base of individual flows. The rate of erosion of interflow areas probably largely controls the rate of retreat of the falls. The amphitheater-shaped valleys common to many of the falls within the Gorge are due to the freeze-thaw action of water from the splash mist that has penetrated the joints. ..." [Norman and Roloff, 2004]


Latourell Falls from the lower gallery Click for short video of falls in action

Latourell Falls were nearly as impressive as Multnomah, and benefited from not having the trappings of tourism that's part of the Multnomah stop. Though not as high and not as layered, Latourell was pristine & photogenic, with lichen giving an entablature formation a splash of color, and the columns on the bottom undercut layer looking like an arrangement of cathedral organ pipes. The 76m plunge is the most unfettered of all high waterfalls in the gorge region, as others tend to impact (horsetail) at least slightly against the vertical rockface. It's one of those beauties where it's hard to take a bad picture.

I'm not really good with coda's, but I can say that there is one dominant feeling I came away with from this trip = I want to go again...but somewhere new. And as gas prices continue their northward march, the western US states are looking even more preferable than they were beforehand. I certainly got to experience a huge slice of basalt geology, which was quite the contrast from the granite geology of my home base. I think the next time calls for a true desert locale, something not really available in my home province (Osoyoos doesn't count). Ahh the possibilities...I just wish they wouldn't butt up against the lack of time & money.

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Columbia Basin Trip: Day 2 - Sisters along the Columbia

2011-05-01T09:41:00.000-07:00

Looping around the Wallula Gap early the next morning, I made a stop at an interesting formation that at first makes me think 'volcanic plug'. Alas, the Twin Sisters are not so, but rather they are the erosion-resistant last vestiges of great flood basalts that covered this particular part of the Columbia Basin. The pillars, which are shaped like irregular molar teeth, consist of vertical remnants of pillow basalt atop a foundation of columnar basalt. Certainly there are other basalt forms in the Gap that also have bits of these remnants still standing, but the Sisters are the largest, most impressive, and least covered in vegetation. As you can see above, their interesting shape spurred native legends & provided some flavor to the geology.

Two distinct forms of basalt make up the Sisters

Every geoscience geek with the smallest bit of knowledge of Pacific Northwest geology knows of the Glacial Lake Missoula floods and their offspring, the Channeled Scablands. The Wallula Gap, its numerous flood basalt flows, and the Twin Sisters themselves were all shaped by the late Pleistocene floods that ultimately found their outlet down the Columbia River. Akin to the Umtanum anticline mentioned on Day 1, compression of the basalt layers created an anticlinal ridge in the Wallula Gap area. An ancient river, precursor to the modern Columbia, slowly but surely cut a gorge through the layers as the gradient increased. Thus we had another water gap created thanks to the steady pace of uplift matching erosion. Of course, once the Missoula outburst floods began, tremendous volumes of water swept down towards the Gap where they were constricted, and thus erosive power was mostly focused on widening the Gap.

For those not familiar with the Scablands, their features & their origins: During the late Pleistocene, the Cordilleran ice sheet advanced into northern Idaho, Montana, and Washington. Gigantic ice dams were formed behind lobes of the continental glacier, holding back thousands of cubic kilometers of meltwater. When these dams broke, huge amounts of water were unleashed, following the path of least resistance through eastern & central Washington, constricting at the Wallula Gap, then funneling down the Columbia River, creating the Columbia River gorge. The last of the floods, called the Bretz flood, released 1600 km³ of water in a two-day period, inundating nearly the entire Channeled Scablands region, and even extended into the Willamette River valley south of Portland, before exiting into the Pacific near Astoria.

Diagram of geographical interaction between Pleistocene ice sheets (blue), Glacial Lake Missoula (yellow), and the full extent of the Channeled Scablands (orange)

I lingered at the Twin Sisters for quite some time on the quiet weekday morning, and I wandered around looking at various perspectives of the palisade basalt, those exposures of basalt along ridges that make it look as if the area is fortified. Ahead of me was a long drive westward on the Columbia River interstate highway, made longer by tough crosswinds picking on my little Yaris. I didn't get to witness or scrutinize much more in terms of geology on Day 2, but the picturesque drive was superlative, and I did notice an interesting phenomenon about the Columbia river that tweaked my hydrologic bone...

Looking west on the Columbia River along I84, just outside of Rufus. Those are whitecaps, not rapids

Winds were gusting up to 70 kph, making it hard to open the car door, but I had to snap a photo of the waves on the Columbia going against the current. That's right, against the current, upstream, eastward. This isn't abnormal or against the laws of physics. All I can see as an observer is the surface of the river, and out of the two forces acting on the surface, the winds are winning...on the surface. Who knows how far down the water depth column the winning force becomes the downstream current? 3, 4, 5 feet, out of hundreds of feet? I couldn't exactly whip out a dingy and a current meter and head out into the frenzied waters, though I wish I could. In any case, interesting food for thought as I travel towards the multitude of high waterfalls that would be the 3rd day of my Columbia Basin trip.

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Columbia Basin Trip: Day 1 - a Lahar and an Anticline

2011-04-29T15:16:00.000-07:00

Only now at the end of April do I have a moment to breath, as two tough terms that went by like a blur have come to their inevitable summer conclusion, and the search for work placement begins. But before the hunt begins, a getaway for a few days was what my figurative spirit called for. I'm the outdoors type (is any geoscience type not?), thus I'm allergic to staying indoors when I have some time off. After perusing through Ellen Morris Bishop's Hiking Oregon's Geology book, I was inspired to try out some of the listed hikes. The trip I took along the Columbia River Gorge was astoundingly beautiful, and the forces of nature were out to make it an interesting few days.

After a few hours driving, the first stop was an aside from I90-East, to visit the roadcut that exposes the Ellensburg Formation lahars (N 47° 06.041 W 120° 41.705). Driving along the windy stretches of central Washington, this slice of roadside geology was quite the treat. The lahar members of the formation stick out quite noticeably from among the semi-arid grass veneer over basaltic lava flows typical of the CRBG region. This lahar exposure, resulting from a muddy mix of water with pyroclastics & ash originating 50km away, is but one example of over a dozen such deposits which have been discovered around Kittitas and Yakima counties.

This particular Miocene lahar deposit has some unique features, including an erratic conglomerate boulder that was carried by the great erosive force, and a plethora of broken-up crossbeds. This is typical of the stratigraphy of lahar deposition, which generally includes a bottom layer of eroded country material, followed by the bulk lahar layer composed of grains ranging from silt - boulder size, and finally the top layer of mostly sand with interbedded bits of gravel & pebbles arranged in a disarray of swooping crossbeds, indicative of a highly turbulent current during deposition. When scrutinizing the roadcut, I could feel the sandy texture, and noticed various discontinuous crossbed forms. The granules were mostly hornblende, feldspar, and some distinct pink Ca pyroxene minerals.

The generic X-sec of a pumice-laden lahar (left); discontinuous crossbed forms near the base (middle, pen for scale); the roadcut along route 10 showing the poorly sorted Ellensburg Formation lahar mass (right)

Shortly after the stop at the lahar was the first hike on the trip, and it turned out to be one of the best hikes I've had in a long time. This is BBC → Beautiful Basalt Country. A tributary creek of the Yakima River canyon, called the Umtanum, has a never-ending trail that takes hikers through a varied landscape of exotic vegetation, eclectic creatures, and fantastical basalt shapes. Obviously I focused on the latter, but tried my best to frame shots to include the colorful blooming trees and the out-of-sync redwoods I spotted. The basalt exposures became more plentiful and protruding the further I hiked in, to the point where I could see plenty of examples of entablature, pillow, and columnar basalt all within a small radius. The multiple flood basalt lava flows of the CRBG that effused throughout the Neogene gave the Umtanum creek canyon its layered characteristics, with varied thicknesses and formational conditions combining to define the Yakima Basalts you would see there.

Example of eroded/oxidized remnants of columnar Yakima Basalts

Boundaries between lava flows is visible on many faces in the Umtanum creek canyon. The purple line divides the lower columnar basalt from the proceeding pillow basalt above. Some surface expression of flows are hidden behind talus or broken up.

Columnar, Hackly, Pillow, all visible on one face

On my way out, a last pullover harkened to me, maybe because my GPSr kept bleeping at me that an earthcache was nearby. Lo and behold a small monument to plate tectonics + fluvial processes in geomorphology. What did it say? To frame it geologically: The Yakima Basalts and Ellensburg Formation lava flows are quite thick, on the order of a few kilometers, and fluvial downcutting into them still has a ways to go (core drilling down 3 km's still hadn't reached a different basement lithology). On top of that thickness, folding into anticlines & synclines occurred due to north-south trending compression. One particular anticline, the Umtanum ridge anticline, is noticeable if you have a good eye for the big picture. It stretches for over 80km, and with such a large scale and broad sweep it might be hard to notice the bend that defines the anticline.

Evolution of Yakima river course during folding

Due to the slow warping matching the slow downcutting of the Yakima river, the river has cut its course through the basaltic layers and created a water gap. The river retained most of its sinuosity whilst doing so, spending its erosive force cutting through the basalt rather than cutting a straighter channel as the gradient increased. Another great earthcache with lots of information and excellent diagrams provided by local organizations, in this case the Washington State Parks and Recreation Commission.

There were other interesting stops along the routes and highways, where roadcuts exposed features and structures that demanded scrutiny. I saw no less than several examples of tilting, faulting, and various forms of basalt in numerous shapes that would make cumulus clouds envious. The vegetation of the Umatilla Plateau & Yakima Folds ecoregions gave a splash of variety & color in springtime that is quite unique and unparalleled. The next day took me into new and interesting places, more CRBG but in different flavors. Day 2 post to follow...

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Learning from the gentry: Maars and Tuff Rings

2011-04-17T17:30:00.000-07:00

Uni classes that specialize in intermediate - advanced volcanism are few & far between in my neck of the woods. Prior to the 4th year courses that dive into rheological properties of magmas and lavas, detailed structures of volcanic landforms, eruption dynamics, and mechanics of volcaniclastic deposition (at least according to the course outline), us undergrads get treated to repetitions of the usual volcanology basics as it pertains to other geoscience disciplines. It gets a bit tiresome going over the VEI for the umpteenth time, and retreads about the same types of volcanoes erupting the same types of lava. Variations within a single volcano don't exist before 4th year, and probing questions are usually met with the full-stop response "But for this course you only need to know...".

Diagram of the various zones and
facies of a maar-diatreme

So I've had to teach myself some ins and outs of volcanism to go beyond the basics. The Firefly guide was a good start, and had more in-depth technical detail than I expected. After looking at some sites in the High Lava Plains of Oregon, I became familiar with features called maars and tuff rings. Courtesy of Jessica Ball, I was pointed in the direction of certain papers written by Volker Lorenz, most notably on "Maar-Diatreme Volcanoes, their Formation, and their Setting in Hard-rock or Soft-rock Environments". It's an excellent read, and lays out the details of these structures as seen in varying locations, plus methods of emplacement during different periods of volcanism. Magma's interaction with various types of aquifers, and how each can produce a different maar-diatreme cross-section is also outlined.

The features themselves might lean towards the esoteric, but when trying to find places of interest that can offer something new to digest whilst hiking around, maars and tuff rings fit right in with tuya's, obsidian flows, lava domes, and other under-appreciated volcanic gems of the landscape. Some of the interesting, more explicit facts I discerned from Lorenz's paper include:

Vast majority of maar-diatreme volcanic features occur in silica-poor (basaltic) volcanic fields
Tuff Rings/Cones are thought of as the phreatomagmatic equivalent of rhyodacitic lava domes
Posteruption, diatremes develop unique stratification of different facies (tuff, volcaniclastics, breccias, sediments, xenoliths)
Maar lakes are generally short lived, as sediment fills in the shallow depression. If one exists, it indicates a geologically recent phreatomagmatic eruption
The greater the volume of the Tuff Ring formed, the smaller the volume of lahars produced in the same phreatomagmatic eruption (subtraction of tuffaceous material from potential flow)
Maars created within a jointed aquifer (hard rock that is heavily faulted) result in posteruptive diatreme pipes that are among the widest, due to block collapse of the hard rock edifice
The center of Maars and Tuff Rings can have a measurable gravity anomaly when compared to the surrounding country rock
The inclusion of irregularly distributed groundwater in the rising magma of an eruption can change the viscosity of the magma, and thus result in irregular eruptions and tephra deposition
Diagenesis (a water-driven metamorphosis of sediments) is frequent in diatremes of kimberlite pipe origin near mid-ocean ridges, ie. olivine can hydrate into serpentine and thus shrink the diatreme pipe diameter

Those points are my interpretation, and I might be off (at least until year 4). The only experience I have with maars and tuff rings is from a trip into south-central Oregon's Lake county. Unfortunately, it was several years ago, prior to my budding interest in the geosciences. However, Fort Rock and Hole-in-the-Ground are excellent stops for marvelling at a standout tuff ring and maar not 10km from each other. They are part of a basin of primarily Quaternary alluvium eroded & transported from the High Lava Plains province/Steen's basalt group. During their diatreme eruptions in the Pleistocene, they were inland lakes, hence their genesis.

Hole-in-the-Ground maar (left) and Fort Rock tuff ring (right), both protected as Oregon state parks
43° 23.314'N 121° 7.919'W will place you smack between the two

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The Chief of a thousand

2011-04-08T22:17:00.000-07:00

The 1000^th geocache is a milestone that calls for a significant effort to find a spectacular cache. I've never been up the Stawamus Chief's backside, and only once have I been up the sheer face when my rock climbing friend hauled my frightened self up that hard way. So up the back of the Chief it was decided, and one of the caches placed on the three peaks would do nicely as the milestone.

On Thursday I had an opening, during a lull in work/schoolwork, to finally get back to nature after 3 months of being sequestered from the intense parts of it. I'd not recommend doing the Chief hike as your first hike in a long while; my thighs are burning and my joints crackling after the 3km→ 600m↑. But I did enjoy myself immensely. The weather was perfectly clear, mild, and the trail had recent maintenance. It wasn't busy but it wasn't abandoned, and one bloke I had a chat with on the first peak was an expat from Darwin who is going to UBC to pursue a postgraduate in materials science (he mentioned to me a Mount Conner not far from Uluru). The caches themselves were easy to find, as the GPSr was on target all day long.

BC Parks info board explaining the Chief's physical geology

Going up such an icon of granite switches my eyes & mind into a geology mode. Up the trail there is little to see besides heavy vegetation and rock rubble. From pieces of the rubble, I spotted some mica schist, granulite, syenite, conglomerate of generally small grains, and of course granodiorite grading to granite or grading to diorite. Indeed a hodgepodge of igneous potatoes with a bit of high energy sedimentary gravy thrown in. One particular opening to the side of the trail halfway up was the home of an oddly placed erratic, which upon investigation appeared to be a 3 meter diameter colluvial boulder of the same lithology as the country rock.

This opening was also the first place to showcase the dominant process that is the hidden danger of the Chief trails → exfoliation. On the farside mountain rockface I could see indication of rockfalls via detachment, and further up the trail there was a couple extreme overhanging weathered blocks that I've termed "jenga granite" (see picture below). Glacial activity during the Pleistocene exploited cracks & joints formed via uplift and exfoliation of the granite family rocks making up the massif. Once the trail started heading straight up the ladders & chains, the general hiking boots were swapped for the rock scrambling shoes, and the surface of the true Chief was exposed to the heavens. The Chief is not exactly geologically spectacular along the top, as what you'll see is mostly weather-beaten granodiorite with splotches of diorite & granulite xenoliths up to beachball sizes. The real treat is the views of Howe Sound, the ant-colony of Squamish, and the snowbound Mount Garibaldi complex. The icing on the cake was not dying on the way down the steep center peak, and not sustaining any injuries after an absence from strenuous hiking. Heading into town afterwards for some goods & services was a perfect time to marvel at the sheer granite rockface that looms over Squamish. A keen eye will spot the darker 'slash' that turned Stawamus Chief from a monolith into a bilith 30 Ma ago.

Examples of exfoliation along Chief trail. Slab detachment on the left, jenga-like sheet fractures on the right

Now that I've hit 1000 I'm a veteran of the hobby, and over the two years I've hunted for those little plastic containers, I've developed some likes and dislikes about it. Thus my forthgoing geocaching focus will lean towards earthcaches plus interesting backwoods/backcountry hikes, and not bothering so much with urban micros and tourist traps.

Why is it every time I see this mountain I think of Babylon 5?

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Field photo Set #2

2011-03-29T11:29:00.000-07:00

Late March - early April is the end of semester period, thus I'm swamped with term papers, labs, and presentations. I'm not one to procrastinate, since I've been burned by it in the past and learned my lesson. But activities like blogging must take a back seat, and I'm sure most reading this blog are experienced in what the last month of a semester is like.

So to keep things simple, for me and for you, but mostly for me, I have another pair of field photos to show, replete with explanation for the features' what/when/where/how. This time, a pair of volcanically-derived features in Oregon, both derived from eruptive activity from the legendary Mt. Mazama complex in what is today Crater Lake National Park.

The Pinnacles fumarole features, looking west.
The V-shape valley shows river erosion exposing them

To the right is a snapshot of the elegant Pinnacles, located just a couple of kilometers to the east of Crater Lake. These spires were ancient fumarole conduits of Mazama's gaseous content (SO₂, CO₂, H₂S), exposed by fluvial erosion from a radial stream, but remaining resistant to that erosive force. Prior to the finale of Mazama's VEI 7 eruption 7.7 Ka ago, a nuée ardente flowed down Mazama's east flank, carrying scoria. Gasses escaped from the settling scoria through fumarole vents, and the mineral content, given the extreme heat, welded loose pumice to the sides of the fumaroles. Thus the pinnacles seen to the right are hollow, and are resistant to erosion from the inside-out, which is atypical of common geologic thought.

When viewing the pinnacles along the 2-3 km path (42° 51.056'N 122° 0.558'W), I noticed that some of the spires had puncture holes in them, in which I could see through. The keen eye will also notice that the base the pinnacles stand on is a lighter color, which is due to the more silica-rich rhyodacite ash falls that preceeded the scoria-laden pyroclastic flow.

This field photo is of a roadcut along the North Umpqua highway, not far from Watson Falls (43° 14.553'N 122° 21.486'W). Catching this roadcut out of the corner of my eye made me glad my car has a low center of gravity. This hillface, ~35km from Crater Lake, showcases silica-rich ashfall from Mazama during its major eruptive phase 7.7 Ka ago. The several-meters thick deposit is a testament to the volume of tephra ejected by the monster eruption (~60 km³), and its coverage across the northwest is found much further afield as well (Mount Baker slopes have a few cm thick of Mazama ash deposit, and it's over 600km from Crater Lake). Tephrochronology analyzes in the region are easily guided by Mazama ash, as the distribution of the ash from the centroid is quite ideal, making it a prime stratigraphic marker for 7.7 Ka.

The white color stems from sanidine feldspar content within the silica-rich ash, and darker grey portions contain a greater percentage of ferromagnesian minerals. The grainsize is quite fine, looks & feels almost silty, with a gritty abrasiveness, but not too harsh and not as hard as sheer-faced plutonic rocks. You can jab this rockface and it feels somewhat padded.

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A glance at Saskatchewan Potash mining

2011-03-24T23:27:00.002-07:00

Saskatchewan might not at first seem like a province that can build itself up as a preeminent world-class supplier of any resource. The population is only 1 million, spread out over a large area, and the climate has inhospitable extremes in the summer and winter. Yet Saskatchewan has built itself up as a leading supplier of a rare-earth salt called potash. Potash is essentially a water-soluble potassium-rich mineral that is often combined with chloride or carbonate, and it has coalesced in abundance underneath the sedimentary platform that defines the geology of Saskatchewan's prairie-lands. The industrial heart of the province has utilized this abundance to strike at rich in a world market where potash is an excellent & cost effective fertilizer for crops, and markets in India, China and Brazil have made it lucrative for the monopoly that Potash Corp. has created.

Why is Saskatchewan so rich in potash?

That question can be answered by looking at the historical geology of the province. During the Devonian period 390 million years ago, southern Saskatchewan was inundated by a restricted inland sea. The equator was also located close to the province, thus the conditions were ripe for evaporation of water in the ancient sea, and thus the leftover mineral content collected and formed what are called evaporite beds. These beds were subsequently covered by later horizontal sedimentary deposits. The capping layers were not too thick, on the order of a thousand meters, thus drilling and mining access to the potash using modern techniques is cost & technically feasible.

World potash reserves, top ten states (left); cross-section of Saskatchewan strata with sylvinite beds (right)

Types and uses of Potash

Potash occurs when Potassium binds with another compound or element to produce a salt. Such compounds include Potassium Chloride (KCl), Potassium Sulphate (K₂SO₄), Potassium Carbonate (K₂CO₃), and Potassium nitrate (KNO₃), all of which have varying uses and grades of quality. Potash has general uses as a bleaching agent, a soap, and a de-icer, and technological uses in computer screens, but the majority industrial use of the compound is as a fertilizer of plant crops. The variations of potash mentioned above are all effective as fertilizers, because plants soak up the nutrients provided by potash when they are dispersed and allowed to percolate into the soil (after being soaked by irrigation). Potash's water-solubility allows this to occur effortlessly, and thus crops will soak up the nutrient content as they soak up water.

Not many countries produce and export commercial-grade potash, and Canada is by far #1 among the ones that do. Importers tend to be heavily populated countries that rely on extensive agriculture to feed their people.

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Earth Story: The Beeb's forgotten geology gem

2011-03-19T13:24:00.000-07:00

I love it when I'm made aware of a documentary or TV miniseries about geology that I hadn't known existed, and I was just recently introduced to the BBC series called "Earth Story", an 8-parter released in the late 90's. A professor showed it in my historical geology class, using an old VHS tape of the program from the university archives. He used it to bring attention to such features as Banded Iron Formations and Stromatolites, and such events as the Rodinian Snowball Earth and ELE's. It's a perfect fit for a class on the evolution of the planet, and certain episodes would fit well in structural geology, geomorphology, paleontology, and geophysics classes, among others.

Naturally, I looked up the rest of the documentary on youtube, and lo and behold found a user's channel with virtually all of them available for ready consumption. I get easily addicted to geo-documentaries that are well presented, and Earth Story has an eloquent Englishman (zoologist Aubrey Manning), beautiful locations and brilliant animations, all prerequisites for a good doc. The series is well structured, with each part highlighting a piece of a particular whole of the history of Earth in geological terms, whilst building a story around revelations about certain phenomena. It has something for everyone, be you a geoscientist of one of the 4 major spheres, or an interdisciplinary. Without further ado, below is a sampling of the available episodes:

This part on Climate change examines Pleistocene glacial advances. Some of the interesting things you'll be informed about include coral reef terraces, foraminifera, smoothed tillite, Carbon cycle & the Carboniferous, Milankovitch cycles, and my favorite of using ice-core samples to reveal Pb atmo concentration during Roman times.

This part on Deep time discusses topics such as unconformities, geothermal gradient, ammonites, radioactivity's role in geochronology, pre-Earth meteorites, Archaean cratonic pillow basalts, lithified mud pools.

This part about volcanoes and the lithosphere examines mantle plumes, plate tectonics, seismic anisotropy, isostatic depression & rebound, mantle mineralogy, mantle convection, the Deccan Traps, Curie point.

This part on mountain formation looks into sea floor uplift, buoyant crust, slickensides, Gondwana's breakup, crustal thickening/thinning, geodesy, lithospheric flexure, serrate/entire leaf edges.

Above is just a small sample of the entire series. Thanks to Kurdistan Planetarium for supplying the videos online. Readers, enjoy!

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My day @ The Western Division of the Canadian Association of Geographers

2011-03-15T11:27:00.000-07:00

On Saturday, March 12 I attended an interesting conference, the Western Division of the Canadian Association of Geographers, with plenty of excellent presentations that both faculty and grad students from a multitude of BC universities. There were plenty of interesting topical presentations to choose from, and with only an 8 hour stretch to fit in nearly 80 presentations, I had to choose 1 out of a possible 6 for every 20 minute time slot. Thus I'm having to send a lot of follow-up emails to those presenters I missed but wanted to hear their findings. One regret is that I wasn't able to catch much of the presentations on BC cordilleran glaciation, but luckily the lunch intermission allowed me to chat with some students on their findings and field experiences.

Figure showing hydrologic response in a coastal western hemlock
watershed. John Martin's investigations found that infiltration of
precipitation is excellent, as the nature of the soil allows for a high
hydraulic conductivity & porosity. Thus heavy rainfall doesn't result
in much overland flow, at least not until the subsurface reaches
saturation, and shallow depressions overtop.

I was able to catch presentations on GIS modeling of landslides, soil loss, and slope mapping of rugged terrain, in addition to my boss's talk on the decrease of agricultural land in Surrey, BC. He showed some maps I digitized, contrasting 30 years of shifting and merging agricultural lots and their tangible erosion in favor of RCI development. Most of the others I attended were on wetland hydrology and lotic ecosystems. The hydro presentations were quite technical in terms of highlighting their results, and quite advanced in terminology, but amazingly I found myself understanding most of what was said. That I attribute to my excellent Hydrology professor (who was one of the presenters), plus the presenters ability to define the important elements in their work. The only one that threw me for a loop was the aeolian physics of sand particles of a vegetated dune, and the subsequent quadrant mapping of their behavior during microclimate wind eddies & gusts.

Thanks to my university's geography department, the cost of the conference was covered, and I will direct the reimbursement to relief of the earthquake/tsunami disaster in Japan. Below is a list of the presentations I attended with, of course, my university profs in bold (gotta represent the alma mater):

Connie Chapman (University of Victoria) - Turbulent airflow and sediment transport over a vegetated foredune, PEI National Park
Parthiphan Krishnan (Kwantlen Polytechnic University) - A GIS for Municipally Enabled Sustainable Agriculture
Terence Lai (Simon Fraser University) - Simulation of Urban Landslides: Cellular Automata approach
Laurens Bakker (Simon Fraser University) - Spatial disaggregation of the Universal Soil Loss equation using Cellular Automata approach
Brandon Heung (Simon Fraser University) - Automated procedure for digital landscape classification based on DEM data
Sarah Howie (Simon Fraser University) - Vegetation variation across lagg forms of raised bogs in coastal BC
John Martin (Kwantlen Polytechnic University) - The Hydrologic response of a small forested swamp complex, North Vancouver BC
Yue-Ching Cheng (Simon Fraser University) - Ins and Outs of Burns Bog: A look into the water balance of a large ombrotrophic bog in the Fraser Valley
Jan Thompson (Kwantlen Polytechnic University) - Management of small water storages: A case study of small farm dams in New Zealand
Steven Marsh et al (University of the Fraser Valley) - Variation of Fraser River, Kanaka Creek, and Silver Creek geochemistry
Maureen Attard (Simon Fraser University) - Progress towards acoustic suspended sediment transport monitoring: Fraser River
Jessica Craig (University of Victoria) - Dendroglaciological investigations at South More glacier, northern BC coast mountains

The study area in Jan Thompson's research into small farm dams in New Zealand (North Island). 39°58.218'S 176°19.850'E in Google Earth will place you around the highlighted watersheds, and by adjusting aspect you can see the drainage regime ultimately has its headwaters in the Ruahine Range foothills. Farmers with small dams (under 4m depth) gather their water mostly from first order streams, and Jan's investigations attempt to ascertain the cumulative effect these volumes will have on the larger whole downstream within the dendritic network, how they will alter the hydrology in regards to water quantity, water quality, downstream sediment transfer, and channel morphology.

I learned lots of new things, not only about technical terminology and equipment used in the field, but also on the sociopolitical state of the environment on scales small and large. With food prices increasing worldwide, food security is coming to the forefront as an increasingly acute issue. In regards to equipment I saw utilized by researchers, I had never heard of using a pharmaceutical device called a Wenglor sensor to count grains of sand, or a device called the ADCP (Acoustic Doppler Current Profiler); nor had I heard of certain equations, such as the Fernandez-Luque and van Beek equation. In essence, attending this conference has given me some extra homework to do, but that is all welcome cuisine for the cranium of this geo information junkie.

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Field photo follow-up

2011-03-02T23:20:00.000-08:00

This is a follow-up to the field photos I posted a month ago, and my best explanation of their origins and processes.

First is a landform located in a gravel quarry in Squamish, BC (49° 43.899'N 123° 06.250'W). Access is via Sea-Sky highway #99. Take a right onto Mamquam Rd. near the Canadian Tire, and travel for 2km up to the quarry entrance, which will be on your left. The geomorphology of what you see below was created when the land in the area was much closer to sea level during the Pleistocene epoch. The environment of deposition was transitional, specifically a delta, represented by visible topsets & foresets. Bottomsets are presumably there, but have not been exposed by the quarrying. Since the region experienced glaciation during the Pleistocene, isostatic depression was the primary force for lowering the area to near sea level, and Holocene rebound has taken it up to its current 100m elevation. Evidence of glaciation is apparent from the mantle of glacial till, which overrode the underlying sedimentary structure during a later advance.

Second is an up-close shot of a granodiorite rockface that includes a granulite xenolith shaped somewhat like a tooth (49° 20.025'N 123° 07.124'W). The rockface is tremendously chemically weathered, turning it into saprolite. This chemical weathering mechanism is not indicative of the current mid-latitude temperate climate of BC, but is indicative of when BC was placed in a more equatorial latitude in its late Paleozoic-early Mesozoic paleogeography. The granodiorite is typical of so much of southwest BC, as it is a plutonic extension of the Coast Range batholith that encompasses the region, and by subsequent erosion has been thoroughly exposed. During its subduction-driven intrusion, the batholiths extensions baked overlying sedimentary & igneous units, and metamorphosed granulite 'polka-dots' became inclusions within much of the granodiorite seen at the surface. Touring Greater Vancouver, one can spot many instances of aggregate that uses the granodiorite w/ granulite xenoliths manufactured for construction and landscaping.

Access to this rockface: Follow Trans-Canada highway #1 west in North Vancouver. Take the Taylor Way exit and make a left turn onto Taylor Way. Head south for nearly a kilometer, and make a left onto Keith Rd. Follow Keith Rd all the way until you pass under the highway, then park and walk down a relatively steep trail to the Capilano riverside.

A couple more field photos will be posted soon, and this time explanations will be included forthwith. And just a small aside, a small rant: Anyone putting up paleogeographic maps on the web please, for the love of god, include major demarcations of latitude (equator, 30°, 60°, poles). It makes a world of difference in deducing paleoclimates.

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Papers I'm reading: Declining sand dune activity in the southern Canadian prairies

2011-02-23T08:48:00.000-08:00

"Visually, the dunes were incredible. They were at least four to five meters in height standing from the top, and there were about four-five rows of dunes. Most of them ran north-south in length. The wind picked up while we were there and I can understand how the dunes are moving so many mm's/cm's each year. The area surrounding the dunes was very desert-like (we spent one night nearby and I managed to get a cactus stuck in my foot, hurt very much). We could also hear the coyotes howl all night and in the morning witnessed several hawks flying by. The area was extremely dry, so much so that I even came across a sort of animal grave yard at the far north part of the main dunes. There was several skeletal remains of what I assumed to be cattle, though the bones were quite small and could have been deer. There were also plenty of little bugs wandering around the dunes, leaving their tracks in the sand, though I couldn't say what kind of bugs they were (although there were many "tiger bugs" I think that's what they are called)."

The above excerpt is courtesy of an aspiring journalist friend who has a keen instinct for the geographic/geologic, detailing an experience among some spectacular sand dunes: Writer's Fidelity

Her description of majestic dunes in southern Saskatchewan segues into the latest dozen-page intellectual nugget, coming courtesy of the Journal of Aeolian Research. The article is titled Declining sand dune activity in the southern Canadian prairies: Historical context, controls and ecosystem implications, authored by Chris Hugenholtz, Darren Bender, and Stephen Wolfe. The paper goes into detail about how the patchy sand dunes located in Southeast Alberta-Southwest Saskatchewan have been seeing a slow but steady decline for the past hundred years or so, and how this decline affects the ecosystem balance and the organisms that reside in the relict landforms:

Sandhills are islands of biodiversity in the southern Canadian prairies that sustain habitat for many rare and endangered species. These unique areas consist of large expanses of dune fields now mostly stabilized by grassland vegetation. Historically, the number of active dunes has decreased significantly due to vegetation stabilization, resulting in a dramatic decline of open-sand habitat for a variety of dune-dependent species. Without a certain level of wind erosion, opportunities for establishment of early-stage, species-rich vegetation types are diminished and open-sand habitat decreases by encroachment of the surrounding grassland vegetation. The current trend of dune stabilization, however, implies that wind erosion is decreasing, thereby threatening the continued existence of a variety of dune-dependent plants, arthropods and vertebrates, as well as other less-specialized species that benefit indirectly from these habitats. By reviewing factors contributing to the historical decline of active dunes, as well as the ecological implications of dune stabilization, the aim of this paper is to establish the biophysical context for new land management strategies that conserve valued landscape components, such as active dunes, and the processes therein. As dune stabilization continues management interventions will be required to sustain or re-establish open sand and the species that rely on these habitats.

Blowout dunes of Great Sand Hills, SW Saskatchewan

You can take a look in Google Earth @ 50° 41.326'N 109° 17.069'W; most of the dunes are of the parabolic variety. The dunes are essentially relics from end of Pleistocene ice ages, notably the Wisconsonian, that have persisted due to a semi-arid precipitation regime and infrequent prolonged droughts typical of the prairies in SE Alberta/SW Saskatchewan. The southern prairies exhibit heavily glaciated terrain, wherein these glaciomarine-glaciodeltaic-glaciofluvial sands were derived from meltwaters at glacial fronts, and the region was subjected to katabatic winds flowing down off the front. The cold, sweeping winds were an excellent local atmospheric mechanism for sorting the sand into dunes.

The paper shows dune activity in 1900's declining due to dune stabilization via vegetation. Provincial action plans to reduce soil erosion has had a lateral effect upon the fragile ecosystem of the dunes and their plant & animal inhabitants. Thus in many ways, it is a "Damned if you do, Damned if you don't" issue, with anthropogenic activities being vastly responsible for currently affecting dune stabilization or proliferation. If left alone, the current climate change trend towards warming & disruption of precipitation regimes would likely lead to an increase in dune areal coverage, but only if decade-long droughts consistently occur. How does that work, though? If humans don't interfere with the dunes, our interference in the atmosphere will allow them to flourish?? In any case, the latter is already assured due to the lag of GHG's.

Ord's Kangaroo rat on sand hills

The real crux of the paper outlines what the implications are for the endemic flora & fauna. Since sand transport is effectively eliminated when vegetation cover exceeds 15%, the fragility of the dunes is acute due to the presence of rare, endangered species that habituate on blowout dunes. Within the paper there is listed over a dozen species of plants and animals in danger of extirpation. Examples include liverworts, arthropods, and the unique Ord's kangaroo rat. The latter is under threat due to dune stabilization allowing predators to corner the rats into an increasingly smaller territory with less space for effective burrowing. The dunes are stabilized by vegetation in a positive feedback mechanism that allows ruderal plants to proliferate on the dune perimeter by increasing surface roughness and changing soil properties to suite further veg expansion → if this goes too far, it will push out endangered dune-loving species like Ord's rat. The endemic animal plays a key role in the food web ecology of the southern prairies, extending an indirect influence outside the dune hills.

Co-operative efforts are underway in the prairies to allow some wind-driven erosion to facilitate natural dune migration & extent, though there is some back-forth wrangling with farm associations that prefer stabilization that protects soil resources. When looking at, for instance, the Great Sand Hills near Leader using Google Earth, you can see how farm lots completely surround the dunes. To conclude my observations, I generally get 3 things out of a peer-reviewed paper:

A new term learned; in this case it was ruderal
A new question raised; in this case how does food security fit into the mix? If prairie farmers are wishing to avoid migrating dunes overtaking their lots, how do we address their concerns while allowing the dunes to flourish?
A new realization; in this case connecting elements to learn how glaciers can form picture-perfect dunes. I knew of katabatic winds, I knew that wind is the greatest terrestrial sorter, and that glaciofluvial is second greatest & capable of transporting & sorting fine sand. Integrate the mechanisms together to make the dunes?....I did not realize that til now.

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Accretionary Wedge #31: "What the heck?!"

2011-02-17T10:28:00.000-08:00

This will be my first contribution to the Accretionary Wedge blog carnival, and as a senior undergrad the topic suites me perfectly: What geological concept or idea did you hear about that you had no notion of before (and likely surprised you in some way)?

basic concept of gravity
when applied to rock density

Thanks to Jim Lehane of the Geology P.A.G.E. for hosting AW#31

For my first two years at uni, previously unknown concepts were a given on a weekly basis. But as my studies get more in-depth, the concepts are becoming more esoteric and/or specific. One concept from those early years comes strongly to mind, as it took me some time to grasp before the metaphoric light-bulb turned on: Gravity Anomalies

My physics teachers would drill it into us that acceleration due to gravity is a constant (@ 9.807 m/s²). GRAVITY, G, IS A CONSTANT! ad nauseum. Then I was eventually presented with an alternate view of the consistency of the constant by my geophysics teacher. I, in my infinite lack of wisdom, and stubbornly sticking by what was told to me by my physics teachers, shirked off his silly idea of minute differences in gravity based on crustal thickness and rock types. I didn't really understand the mechanics of it the way he explained it, and it was never really tested on us students.

The true revelation came during a summer volunteer expedition with a local CGS glaciologist. As one of three heading up to the Matier Glacier within Joffre Lakes park, I got a taste of what experts do, and what instruments they use to analyze receding glaciers and the mountains they rest on. I found out that one such device we lugged up to the top, a microgravimeter, measures the gravitational field at a point. So the glaciologist operated it, got the reading in milligals, and I stood there dumbfounded. He was gracious enough to explain to me the concept of gravity anomalies...how it relates to crustal properties (such as thick, light mountain roots & thin, dense old oceanic trenches), and how we get the Bouguer anomaly, derived from measurements/corrections.

"Rocks have different densities, eg. felsic - ultramafic, and compression of the crust via plate tectonics can thicken the crust, developing structural mountains with or without igneous intrusions. These mountains have thick roots, sometimes 30+km from peak - basement. When such a thick mass is composed primarily of lighter granites, its lighter density is less of an attraction than when compared to a thinner, denser mass of heavier basalts. Denser basalts are found near subduction zones, especially above deep trenches. The phenomenon is comparable on continents as well: The Deccan Traps of Maharashtra measure a noticeable difference in gravity compared to the Himalaya ranges in Uttarakhand."

Upper Joffre lake. Behind would be the tongues of the Matier Glacier.
This is where I learned about gravity anomalies, luckily not by tumbling down to the tarn

Thus I was enlightened to a concept that had previously been muddled in my brain. I've even had a couple opportunities to apply it to my personal and work projects (ie. Cornwall geology post). It's become an increasingly seen concept in higher level textbooks I've perused, and more and more diagrams & cross sections that have caught my eye combine topographical profiles and Bouguer anomaly milligal values (example below).

Simple profile showing Bouguer anomaly values with general topography across the US

In retrospect, I wish I had a time machine, so I could go back and tell my junior undergrad self about how not to take anything for granted in the scientific studies. Geology always seems to smash preconceptions built up by the other science disciplines, and that's something I love about it. For anyone interested, Britain & Ireland geological survey's have done some extensive gravity surveying, and documented some interesting positive & negative zones. Check out the additional links for it.

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Picking the best place to live, geologically speaking

2011-02-14T09:47:00.000-08:00

I rarely get to have discussion with human geography students, but the natural hazards class I recently completed had a good spread of the physical geeks with the human geeks. One human friend mentioned how she lives in a neighborhood on the edge of a broad alluvial fan, and that her parents have little clue as to the potential dangers of living on such a precarious foundation protected only by modest dikes, which I might add have had increasingly shrinking freeboard values for the past two decades. The deflecting reason they gave her is that "developers would not have built here if it wasn't safe".

Oh no, they would. Developers hedge their bets, and most in our regional district tend to downplay the importance of geophysical reports. Developers will push through proposals with hard cash to get the required zoning, especially if the 'view' and location is something that will bring them big bucks. This is not to say that they will cut corners wherever possible, as most of the time construction is top-notch, corresponding to strict standards for quake-proofing and packing down the sediment if the foundation happens to be laid upon Holocene alluvium.

Where is this post leading? Well, in my humble opinion prospective home owners have to take on some proactive responsibility themselves. Common sense dictates that the buyer beware, and there is no excuse for an educated westerner who does have the rights and the access to geophysical information to not take some time and look at it. Where I live in beautiful British Columbia, our own provincial division of the Canadian geological survey has done some excellent work on investigating factors that determine how damaging certain natural hazards are in certain areas. Below you'll notice fragments of a poster that outlines the traffic-light approach to categorizing hazards:

Slide hazard map of Greater Vancouver.
Light green circles indicate known slide occurrences

Liquefaction hazard map of Greater Vancouver.
Red zones mostly correspond to deltaic and alluvial deposits

Flood hazard map of Greater Vancouver.
The red zones are deltaic and alluvial plains, and have experienced little uplift
since the fill is mostly Holocene. The grey zones are Pleistocene glacial uplands,
mostly till, and benefit from tens of meters of thickness + isostatic rebound

Tsunami wake from Jan 26, 1700
megathrust quake. Ghost forests
attest to unbuckling of plates,
causing meters of subsidence

Looking at this one source of credible information already alleviates a lot of concerns a potential home owner would have, especially in our tectonically active region. Sure we haven't had a big one in living memory, but that doesn't mean we are out of any proverbial woods. On the contrary, the lack of moderate quake activity off the coast of Vancouver Island has led geophysicists to investigate and conclude that the Juan de Fuca plate & North America plate are locked at the shallow subduction contact, and tension is building to an inevitable unbuckling. Whether that results in one huge snap of a megathrust akin to the 1700 Cascadia quake, or a series of smaller unbuckling motions is yet to be seen.

I was asked if I chose where I live because it is among the safest spots in the region. I reside on the glacial uplands, on the crest of a street with a gentle slope. Alas, as a student with a limited budget and only part-time jobs, I cannot claim that I was so smart to have chosen such a safe spot. It's pure coincidence, I chose it because I could afford the rent. But I have dodged a bullet, so to speak, by digging for this knowledge and taking it to mind before I do make my first home purchase years from now. I've already compiled a short list of personal rules for where a home should be, to which additions will slowly be added:

At least 300m from shore
At least 50m asl
Not adjacent to any slope greater than 25°
Not on any faults, not even ones considered “inactive”
Not on any META bedrock that has extreme foliation
Not on any SED bedrock where bedding planes are poorly indurated
Not within the boundaries of a 1 in 50 year floodplain
Not within the boundaries of a 1 in 100 year floodplain if recent evidence has shown urban development has forced flow to concentrate, and thus freeboard values for dikes are consistently less than 2 feet
Not on any foundation that has a layer that swells when saturated (ex. Bentonite)
Observe wind direction patterns if living on or near a sandy desert or high altitude snowy area, to avoid home being buried by windblown material
Not on any bedrock that has a lens of limestone beneath (GPR should discover it), lest it dissolves and a sinkhole forms
Not within a radius of 300m from the edge of a forest prone to fires. Consider making the perimeter of your property fuel-free

I know a few of these are not economically feasible, but I've tried to arrange them in what I consider their order of importance, and the first several are free provided some time and effort and some light education. The GPR might not be an option, but if buying a $seven figure$ home, it's worth it for peace of mind. Above all else, look at the hazard history of the area you're moving into.

I'm not touching on atmospheric hazards, but they should be looked into as well. They're kind of a big deal too.

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To study or not to study: a Metamorphic Genesis or a Dynamic Creek?

2011-02-08T11:10:00.001-08:00

Lately I've been thinking about what topic I should choose for doing my senior undergraduate major project. This project is essentially worth 3 credits, or one full course. The synopsis outlines it as almost a thesis but with a narrower scope of time, and only to be peer reviewed by my university professors. I'm planning on it for this semester next year, but want to utilize the coming summer months for field work.

The first idea that comes to mind is to measure/analyze something local. I don't want to synthesize and regurgitate some phenomenon that is a world away where I can't put my hands on it (I do that enough on this blog). After all, one of the big reasons I chose geology is because on occasion the laboratory is the great outdoors. The second thing that comes to mind is that I want to break new ground. Not by finding new analytical methods or a stunning new hypothesis (I won't have the time, funds, knowledge nor experience to do that for several years), but by covering something in greater detail than has been.

I might have access to basic hydrological equipment: current meter plus pH, conductivity, and DO probes. In that case I wish to study the fluvial geomorphology of a particular large creek that has not had a thoroughly holistic study. Plus my favorite geology book is Leopold's, and this would give me an excuse to read it again. Its geomorphology is of particular interest because the creek cut a channel down through glacial till and exposed a volcanic basalt layer underneath, thus a small portion of its mid-reaches has step-pool falls. More details found in the earthcache I created for it.

Cliff falls in Maple Ridge, BC. Kanaka creek pinches
here due to eroding down to a resistant lava flow

If access to equipment or most of the drainage basin is not possible, I am considering doing a petrological study of a pre-Jurassic [mostly] metamorphic group on the north shore. There is surprisingly little information about it, beyond a few journal papers making slight references to it when describing other groups/formations that interact with it. This would involve a thorough investigation of approximately 8 sites of varying size (see map below) where outcrops have been identified, plus I'd get to use snazzy terms like aureoles and metamorphic facies. All I'd need in that case is a rockhammer, a handlens, maybe a petrographic microscope.

Surficial geology map of North & West Vancouver
#1 is the Twin Islands Group I'm considering for study

I'll likely put this on the back burner until late spring, when I will have time to investigate the creek and gauge how I can approach it from various access points. In the meantime, professorial advice and anecdotes will likely sway me towards one or the other.

Terminology note: It took me a while to wrap my head around the phenomenon of roof pendants. Sometimes a blatantly obvious mechanism or concept eludes me, until a light bulb goes on. This has happened with things like pedimentation, cyclothems, Benioff zone. My best attempt to explain to myself the idea of roof pendants - When a batholith forms below overlying strata, it penetrates upwards, and thus makes contact with those layers. The layers will likely undergo contact metamorphism, and metamorphose under high temperature & low-moderate pressure. Erosion of subsequent material leaves the META members as isolated crops dangling/resting above the batholith. Essentially roof pendants have a parent rock, and are akin to xenoliths on a large scale but did not get included into the igneous mass, simply resting above it instead.

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Field Photo Tryout

2011-02-03T10:50:00.000-08:00

It's inevitable that a geo-geek will want to show off their collection of field photos. They generally show rocks, structures, facies, principles etc... tells a story and is a lot more interesting than showing a box filled with collected rocks & minerals, which in my opinion is tedious through the internet.

Thinking about how to present them, I'm stuck between two methods I've seen other bloggers use: show a photo and give a complete explanation of what/when/where/how, or allow readers a shot at figuring out the what & how of the elements in the photo, and filling them in on the rest later on. So as a tryout, I will initially go with my preference, which is the latter. Below are two field photo's I've taken in southern British Columbia:

Field Photo #1 (height of photo =10m)


What do you see here? (hint: two distinct depositional environments are shown)

Field Photo #2 (GPS = 15cm tall)

What do you see here? (hint: mechanism at work on both rocks)

Dunno if this format will work or not. Heck, I don't know if I have enough readers yet. But those who do read, feel free to take a stab (or rockhammer) at it in the comments. I'll follow-up later on depending on response, and change method if preferred.

Learning from the gentry: Banded Iron Formations

2011-02-01T10:20:00.001-08:00

I've only ever seen one of these, when vacationing around Lake Vermilion in Minnesota in my late teen years. At the time I had no idea the origins of the rock nor the processes that went into making the multibanded swirls. Luckily I found an old photo taken around a shore of the lake during a respite when my family was canoeing.

BIF outcrop on Lake Vermilion, Minnesota

The outcrop I happened to stop at shows a Banded Iron Formation that's quite deformed, with an identifiable fault, folding, and a series of what appears to be aplite cross-cuts that, if I recall correctly, were a few cm's thick. This was before the days I knew to put an object in the frame to define scale.

I have a novice understanding of BIF's, but novice doesn't cut it anymore, especially in the latter half of my degree pursuit. So, armed with more experience and resources, I delved into a deeper understanding of these interesting Precambrian rocks. Hopefully it helps for my Structural Geology course, and takes me from BIF novice - BIF intermediate.

Banded Iron formations are a unique rock strata that is formed of alternating bands of iron-rich layers interbedded with iron poor silica layers of mostly chert. The amorphous silica is typically entrapped by iron oxide laminae to form bands of chert. The bands always alternate, and have minimal comingling of particles/minerals at the boundaries. Studies have found that the boundary between the iron-rich layers and the iron-poor silica layers is distinctly abrupt, even on a micrometer level. Each band can be millimeters thin to meters thick.

The mineral content of the iron-rich layers have hematite and/or magnetite and/or siderite, whilst the iron-poor silica layers can have varying mineral content depending. This diverse mineral makeup of the siliceous bands, coupled with an additionally diverse array of trace & guide fossils, has spurred plenty of research into the origins of individual BIF's....whether the silica content is derived from continental erosion/deposition or oceanic currents or a dynamic mix of the two. Most Banded Iron Formations are dated from 3.8Ga (early Archaean) - 1.8Ga (late Paleoproterozoic). That's plenty of time on Earth, and thus most are of a highly deformed variety (discussed below). There is a widespread connection of deformed BIF's to the major greenstone belts of the world, thus establishing a likely mafic origin of their parent rocks. Because of their age, BIF's are found mostly in continental cratons, and all continents have one:

In North America, the aforementioned Vermilion area (47° 49.679'N 92° 14.358'W)
In South America, the Guyana shield near Port Kaituma (7° 39.824'N 59° 51.393'W)
In Europe, the Voronezh Massif of the Ukranian shield (49° 16.685'N 30° 20.518'E)
In Africa, the Liberian shield (6° 48.427'N 10° 18.602'W)
In Asia, the state of Karnataka on the Indian craton (15° 3.781'N 76° 35.442'E)
In Australia, the Yilgarn craton of Western Australia (26° 35.627'S 118° 29.693'E)
In Antarctica, exposures of Mount Rucker on East Antarctic craton (78°11.000′S 162°32.000′E)

The oldest one (3.8 Ga) is found near Isua, Greenland (60° 20.788'N 45° 26.724'W).

Various Precambrian shields of Earth

Most studies conclude that the source of iron for the formations is from hydrothermal vents (black smokers). In a cyclical mechanism, iron was scavenged from the oceanic crust and re-deposited on the ocean floor by hydrothermal fluids. High-temperature hydrothermal alteration of early Archean oceanic crust played an important role in the deposition of the formations. Also playing a role in the construction of the alternating bands was the buildup of siliceous material near the black smokers, which eventually led to submarine landslides that covered the iron-rich layers. Those layers were evened out with the assistance of turbidity and deep ocean density currents, as seen in the following diagram:

Hypothesized steps to achieve alternating bands of iron-rich & iron-poor layers

Favored depositional environments for this style of Banded Iron formation mechanism include island arc basins on flanks, back arc basins of convergent plate boundaries, and rifting zones that developed within Archaean cratons. Thus deposition occurred in a shallow marine environment under transgressing/regressing seas, and even possibly on continental shelves of passive margins.

Just like every facet of any geological discipline, there is categorization that has emerged for Banded Iron Formations. The two different classes, derived in 1983, are of course named after where they were first studied in some detail. First we have the Superior-type sequences; not hard to figure out where those were discovered and what craton they belong to. They are thought to be deposited in shallow marine environments as largely granular & oolitic iron-formations grading into laminated iron. Deposition was primarily in adjacent basins surrounding the perimeter of uplands that projected above sea level, and seen today the type is relatively unmetamorphosed and undeformed, with widespread uncovered outcrops alongside such members as conglomerate and quartzite rocks. That is indicative of environments that were high energy, but that somewhat buffered the shield BIF's deposited in basins from marginal deformation. Secondly, we have the Algoma-type sequences, named after another part of the Canadian shield not far away from Superior (northern Ontario), and deposited in deep marine environments. Algoma BIF's are highly metamorphosed and deformed, and considered to have parent rocks that were volcanic in origin, thus they reside in extensive greenstone belts where other volcanic entities (ex. pillow lava) are adjacent to them, and their outcrops are more discontinuous and klipped relative to the Superior class.

That was all the nitty-gritty foundational details of Banded Iron Formations, however the genesis of their unique thin bands is apparently one of the more highly debated topics in current paleogeology. Looking through online journal sources, there seems to be repetition of two major hypotheses as to the precipitation of the iron-rich layers. One approach to precipitation of free iron produced by black smokers involves a downward diffusion of CO₂ that intercepts the iron upwelling from deep waters, resulting in a chemical reaction between the compounds and thus preventing iron from reaching shallow waters. This posits diffusion of CO₂ as an even process in the Archaean/Proterozoic Earth, or at least for the time given for creation of banded iron formations, so that we observe the iron-rich bands as an expression of a downward diffusion of a finite volume of CO₂interacting with the iron; following that is either the quiescence of hydrothermal vent activity or heightened depositional activity from terrigenous sources or a combination of the two.

An emerging hypothesis involves anoxygenic phototrophic organisms living beneath the ocean's windmixed surface layer, and these organisms precipitated the free iron provided by black smokers into iron oxide, an explanation for BIF deposition in a stratified ancient ocean at a constricted depth of a few hundred meters. One of the links in the additional info leads to a paper where geochemical analyses has derived a thickness of the layer where these phototrophs must live to both stay below cyanobacteria above and still get enough sunlight penetration. These phototrophs living below a mixed layer inhabited by cyanobacteria could have been responsible for the absence of iron in shallow waters and for Precambrian BIF deposition in a stratified ancient ocean. Take a look:

diagram of layers involved in precipitation of Fe₂O₃ by anoxygenic phototrophs

The phototrophs work hard when the hydrothermal vents pump out the free iron, and thus the paper considers the alternating bands evidence of either hydrothermal quiescence or a seasonality mechanism in the early Earth atmosphere.

The several papers I've read tend to focus highly on the quantitative geochemical elements of Banded Iron Formations, and are lacking in observational geological elements. Essentially the linking between the two facets is limited so far, and such a key connection is hopefully what future studies will focus on. As far as I'm concerned, I simply wish to have more first-hand experience with BIF's, but unfortunately for the time being I reside in a geologically young and active area, which is the polar opposite of the geologically old and inactive areas where you find these beautiful swirling rocks.

Additional Info:

The strata of Egypt??

2011-01-28T11:51:00.001-08:00

I don't think I've ever seen a satirical use of a stratigraphic cross-section before, but last night I caught the Daily Show and this funny block diagram (Stewart remarked about how it was a great untapped reservoir):

There can be a lot of comedy in geology if one looks for it, notwithstanding all the unintentionally funny misspellings of terminology.

Disclaimer: I'm not making any political or religious comment about the situation in Egypt, I'm simply amused by the combination of satire & geology, and I hope readers are as well

Looking through the archives: My poster on the Geology of the Southern Appalachians

2011-01-25T12:12:00.000-08:00

This was the first poster I ever did for a geology-related course. At the time I thought the idea was a bit silly, but in retrospect and with more exposure to the world of geologic academia, I realize it is an essential tool in showcasing research. Nowadays my apartment walls are teeming with geomaps, cratonic maps, deep time diagrams, rocks & minerals picture tables, etc...

Interestingly I made my first draft of this poster by staying up at nights in New Mexico hotels during a geology-heavy vacation there, and thus I started fiddling with making one for the state. Saved me some time for a later course. If you want to take a look, click on the above thumbnail for the poster, and download the poster file (format is Powerpoint .ppt). References are available here

On the Geology & Topography of Cornwall

2011-01-22T00:02:00.000-08:00

Recently completed a spatial analysis of Cornwall. While scrutinizing the land, naturally my mind wanders towards investigating the county's geology. What I found was quite a unique hodgepodge of different mechanisms & features which make Cornwall quite distinct from the other 7 counties in the southwest of England that I have also done analyzes for.

Land's End headland on southwest tip of Cornwall.
Resistant sandstone has been shaped by erosion into pillars

Upon sweeping around the place, I noticed how similar land development was to, well, every other county I've looked at. Towns are few, with farms taking up about 90% of the land, with quarries scattered here and there (you'll find out why further down). Being on the southwest peninsula, Cornwall is exposed to the brunt of the Atlantic's influence, so winds are consistent and the temperature & precipitation regimes, thanks to the Gulf Stream, are mild and broken up only by occasional storms. Headland erosion is a process that has made a home in Cornwall, with the northern coastline getting pounded with more voracity than the south. The geomorphology of the northern coast interchanges between sandy beaches and steep cliffs (High Cliff ~240m face; sandstone cliffs near Bude). Resistant metasandstones at Land's End, morphosed due to contact metamorphism, highlight some of the rugged coastline typical of Cornwall. The southern coastline is more reserved, with more gradual gradients from the interior hills and more fluvial delta deposition. Energy from erosive forces have in past periods focused more on the south, so wave-cut platforms are more prevalent.

Looking to the interior of Cornwall, which is never greater than 50km across, one notices broad open landscapes broken up occasionally by tors and moors. These are the result of a granite underbelly that interjected pluton masses from a large batholith, formed during the coming together of our last supercontinent Pangaea. The tor/moor uplands contain quite acidic soils fueled by detritus of granite parent material from the plutons, and serve as the gathering point for headwaters of most of Cornwall's rivers. Bodmin Moor is a textbook example of broad radial drainage pattern from a high peak.

Cornwall surficial geologic units

To set the stage for Cornwall's geological underpinnings, I have to start back in the Devonian when marine sand was being lain down, preparing for its inevitable lithification and rapid uplift (is there any part of England without Devonian sandstone?). The mechanism to bring it above sea level was the Variscan orogeny of the Permian, northern Europe's part of the formation of Pangaea, with a mobile belt stretching in a northeast trending arc from Portugal - Poland. The orogeny uplifted the sedimentary basins, and also introduced folds & faults into various sedimentary formations throughout Cornwall. One particular fold is visible near the aforementioned town of Bude on the northeast coast, where a picture-perfect chevron fold shows the changing direction of thrusting during the length of the Variscan. The only Precambrian rocks exposed at the surface in Cornwall are scattered remnants of Man of War gneiss wherein Phanerozoic strata eroded to expose them; those are mostly found in the tors and moors of the Cornish uplands.

Chevron folding at Millook Haven, part of the Culm Measures formation

An ophiolite was also uplifted during the Variscan, but surprisingly its emplacement/obduction upon the southwest tip of Cornwall was not part of the closing & consumption of the Paleotethys ocean. Rather it was already there, dated to the Devonian and coinciding with the subduction of an arm of the Prototethys. This Lizard complex ophiolite, which is discussed further in this post, was named after the Lizard peninsula which serves as the southernmost extreme point of mainland England @ 50°N 5°12'W.

Cornwall truly differs from other county's in England based on what underlies the strata, and that is the Cornubian Batholith. The Cornubian Batholith (using the Roman name for Cornwall) is essentially a discordant granite batholith that has roughly 8 plutonic extensions that have intruded into the upper crust and been exposed via erosion (though some remain submarine). The batholith emplacement has been dated, using typical radiometric techniques, as Permian, thus matching the theorized Variscan orogeny. The mechanism(s) of emplacement/intrusion into the overlying sedimentary strata are still under debate, with different hypotheses for plutonic injection/growth. There is one concerning a typical diapir mechanism, one that favors feeder dykes supplying magma that was kept hot enough via frequent injections into laccolithic or lopolithic structures in which the shape of plutons were controlled by fault geometry, and finally a hypothesis that favors partial melting and branches of lamprophyre dykes as the source of pluton material via access to mantle magma through a network of extensional faults. These various methods are highlighted in the "Geology of southwest Cornwall" website link, which happens to be someones doctoral research into 'The Tectonics of Variscan Magmatism & Mineralisation in South West England'. It goes into extensive detail about the batholith's petrology, mineralogy, etc... Ultimately the complex of plutons intruded into the Devonian - Carboniferous sandstones above, and as one would expect there is plenty of contact metamorphism that produced schists & metasandstones surrounding the fringes of the plutons.

Cornubian batholith granite outcrops. Diagram shows negative
gravity anomaly caused by granite plutons having a lower density
than surrounding metasandstones & schists + uplift of the terrain

First-hand accounts of geologists examining the tor rocks of the plutons denote that what is visually obvious at first glance is numerous megacrysts and sandstone xenoliths (remember back to early days of first-year earth science for the principle of inclusions and aphanitic - porphyritic - phaneritic - pegmatitic crystal formation). Computer modelling, gravity anomalies (above figure) and density contrasts reveal a total volume for the batholith of 68,000 km³. The overall appearance of the batholith is a tabular body, which is 50-60 km wide at its base, with steep sides, a sloping base (possibly tilted 2-3° further south during post-emplacement movements) and an irregular upper surface that is continually being shaped by denudational forces. Think of it as the area of Cornwall + Devon, but with a depth of sea level - Mt. McKinley.

The batholith has resulted in mineral richness for Cornwall, with mining operations throughout the last century acquiring mineralized Silver, Copper, Lead, Tin, and Zinc, along with quarrying the ammonium-rich granite and kaolinite, that nice soft moldable clay mineral that provides us pottery and loo's. A lot of the mineralization comes from metasomatism processes that allowed elements to coalesce from mass fluid movements.

The icing on the Cornish geology cake has to be the Lizard complex ophiolite, located on the southwest tip of the county. It was obducted onto the protocontinent of Laurasia in the Devonian, and sheared by thrust & extensional faults, especially during the Variscan orogeny. It's true that the vast majority of ophiolites are rarely an intact specimen from META/IGNY basement - pillow basalts on top, but amazingly the Lizard does not stretch its oceanic crustal segments over a large area, certainly not compared to the ophiolites I've studied in the southern Appalachians as part of the Alleghenian orogeny.

Lizard peninsula in Cornwall. Blue line
represents Helford river, a ria that prior
to the last ice age was a true river flowing
along a normal fault

The current composition of the ophiolite fragments are serpentinite, amphibolite, and schist facies, respectively representing the harzburgite basement, the gabbro magma chamber, and the sheeted dykes. There's even some high grade gneiss found in the Goonhilly Downs, which is derived from the Man of War gneiss mentioned previously. Pillow basalts are still pillow basalts for the most part, though they were poorly preserved in this instance. Topographically the peninsula is mostly a raised platform between 50 - 100m, with the Goonhilly Downs satellite dish network (a future space science center) at the highest part. The serpentinite material, along with poor drainage, has given rise to a heathland where dwarf shrubs dominate due to the basic soils (ex. Cornish heath).

Whilst doing some work involving the European Soils Database, I distinctly noted the properties of Cornwall's soils. Looking at the parent material, slate and metasandstones are prevalent for the majority non-moor expanses, whereas acidic soils from the granite plutons make up most of the rest; patchy spots of boulder clay are the only unfeasible spots for agricultural activity. Very thin layers of loess are widespread on the Lizard peninsula. When compared to the rest of the country, Cornwall has quite a shallow depth to rock + a medium-strong erodibility class. Since uplifted sedimentary basins make up the majority of Cornwall's surficial geology, the eroded sandy overburden makes for decent aquifer material, allowing for a high topsoil & subsoil water capacity that is easily available for crops and other plants to soak up.

To conclude this post, I would have to say that observing Cornwall has been a treat. It wasn't immediately unique compared to the rest of southwest England, but after several minutes in I started noticing the big differences, and along with Devon it makes up a distinct geological history from Devonian to the present. A granite backbone, tough sandstone cliffs, and an ophiolite to boot. Makes it a treat to write a lengthy post about the county ... as a way to have a deeper understanding of the place I'm analyzing and to just plain learn more geographical geology. I invite anyone also interested in European history to look into Cornwall's Celtic heritage, and how the Arthurian legends are tied to the place. Those cognizant will certainly know of Tintagel Castle.

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"Indians!"

2011-01-17T11:03:00.000-08:00

What does the geo-minded individual focus on in a movie, especially one with beautiful scenery ripe with geologic history? When I was a younger man, I wouldn't give much thought to what I was looking at and how it's possible for landscapes to be like that, and in any case the action and story would (or at least should) keep me enthralled. But after spending a few years immersed in various topics and sundries of geology, I started catching myself paying attention to the places rather than the people, especially when showing open country. Certain flicks have DP's who photograph and Editor's who showcase the filming locations in such breathtaking sweeping visuals that I cannot help but let the mind wander off from whats going on screen and towards the realm of the geologic.

What part of this scene are you looking at? (photo courtesy Universal Pictures)

Sometimes I'll even buy a DVD of a mediocre movie simply because it had plenty of outdoor visuals of a spectacular natural wonder or formation/group (ie. The Canyon) or what-have-you. Plus I'm always checking the filming locations on IMDB as a kind of geography jeopardy with my sweetheart. Then its off to Google Earth to match the cinematography with the real place (recently spotted where Tom Hank's island in Cast Away is located).

One thing I wish movies of this new decade would focus on is a return to the Western genre. Every current and inspiring geologist should be a fan of Western's but for their displays of the untouched parts of the American West. Now off to watch The Missing.....for the Valles Caldera & the few seconds they show a rhyolite lava dome in the valley.

Papers I'm reading: Expansion of Juneau Icefield glaciers in late Holocene

2011-01-14T00:03:00.000-08:00

Being a poor undergraduate student, I tend to savagely bite my pocketbook whenever I plunk down for some new textbooks or access to academic papers. Amazon has become a great source for affordable books, but when it comes to papers, the search for freely available ones is like a search for lost treasure. Whenever I find one, its like finding the pot of gold at the end of the rainbow. More often these days I am finding free papers, usually from professor recommendations, blogs, and branching out from the Wikipedia hub. I'm not a complete cheapskate – I purchased Anne Jefferson's paper on Hydrology & Topography of Oregon's High Cascades, and reading it actually led me to visit the primary site (Pacific Crest trail to Belknap Crater) when I was last in Oregon.

My geomorphology professor happened to be a glaciologist, who tends to drop off the face of the planet during his ventures to Greenland & Antarctica (he's down in the deepest south now during the window). He sent me word of some freely available papers he authored, and I took a look at his latest paper, dealing with the advance or retreat of glacier tongues in the Juneau icefield during the late Holocene (CE years), and how the chronology of those movements challenge the term "Little Ice Age". I'm wide-eyed when reading these and actually understanding most of what is said (though details of mass spectrometry still confuse me - I need access to one to play around with).

Llewelyn glacier w/ finger
of Atlin Lake
Radiocarbon and dendrochronological dating of glacially overridden stumps and detrital wood indicates that two outlet glaciers of the Juneau Icefield advanced shortly before the ‘Little Ice Age’. Tulsequah Glacier advanced to within 2.4 km of its all-time Holocene limit between ad 865 and ad 940. Llewellyn Glacier, one of the largest glaciers in British Columbia, advanced sometime between ad 300 and ad 500, and reached to within 400 m of its Holocene limit between ad 1035 and ad 1210, well before the climactic, ‘classical’ ‘Little Ice Age’ advances of the past several centuries. Our data show that some glaciers in western North America were extensive and expanding at times when alpine glaciers have, in the past, been assumed to be restricted. The evidence raises questions about how to define the time of the beginning of the ‘Little Ice Age’ and, perhaps more importantly, about the utility of the term.

As you can read in the above abstract, the authors postulate that the Little Ice Age period, roughly 1600-1900 CE, is too vaguely defined to be properly used in geologic circles considering the variations in glacial extent in the Western Hemisphere. Taking a look at historical conditions of both the Llewellyn & Tulsequah glaciers, they find their furthest extents occur during the established Medieval Warm period, roughly 950–1250 CE.

Map of Juneau Icefield,
studied glaciers labeled

Moraines and ice-dammed lakes are utilized to define the geomorphology of the glacially-carved valleys. Dendrochronology and radiocarbon dating of ¹⁴Carbon isotope was heavily used (and I do mean heavily), for detrital wood caught in morainal till and diamicton layers. Death of subalpine fir (Abies lasiocarpa) was used to date advances of glacial tongues, bulldozing vegetation along their course.

The Landsat image below highlights a portion of the study area, showing Tulsequah glacier and how exposed land is confined to a constricted valley that is essentially the glacier's foreland. The Tulsequah river flows into the Taku river, which then flows into the sea around the Alaskan panhandle fjords. The 'Rock Ridge' is a till-covered roche moutonnée, from which many samples of stumps were used for ¹⁴Carbon dating. This is all viewable on Google Earth; check 58° 38.00'N 133° 33.00'W (Tulsequah & Taku confluence) and move in a NNW direction up valley. The gradient of the valley is a bit below 1%.

The general stratigraphy involves a mixture of glaciolacustrine sand & gravel overlain by diamicton and glacial till, which pressed into fractures of the lower lacustrine layer, forming clastic dykes. A thin veneer of modern glaciofluvial gravel-grading-to-silt is the icing on the cake in some parts of the river valley.

I generally get 3 things out of a peer-reviewed paper:

A new term learned; in this case it was Ecesis
A new question raised; in this case How does this evidence correlate with accumulation/ablation for alpine glaciers in the same time period for the Coast mountain belt?
A new realization; in this case clastic dykes → glaciotectonic fractures/deformation are more important in the field studying of glaciers than I thought (maybe because this very professor downplayed them)

Below are some links about Juneau icefield research, and the paper itself @ Sage journals. Sorry for the pay site, but I couldn't clarify with the author before he left for Antarctica if I could provide a link to a free copy.

Additional Info:

Neptunist vs Plutonist

2011-01-10T07:26:00.000-08:00

Brian Romans over @ Clastic Detritus was recently selected as a finalist for science blogging due to his post about Rapid Canyon Formation and Uniformitarianism. The Uniformitarianism vs Catastrophism debate is likely familiar to every geo-blogger, or quite frankly anyone who has taken a historical geology course or read about the 19^th century debate. The argument seems quaint and anachronistic these days, but the human condition seems to often unnecessarily dig up old black & white positions on topics that have already moved light-years beyond. I guess cherry-picking ignorance doesn't seem to have a retirement age. This is not to say that we should ignore old debates, as understanding the evolution of the school of geologic thought serves as an important reminder about how methodologies and discussions should and should not be approached.

One item that popped into mind when thinking about Uniformitarianism vs Catastrophism was the preceding debate over the origin of the Earth's crust and its variations of bedrock (IG, SED, META). Neptunism vs Plutonism was a classic geologic debate that showed the value of field work and how direct evidence gathered from it strengthens a hypothesis. Geology and its various branches literally just don't work without field study.

The Neptunist view of the origin of the solid Earth was spearheaded by Abraham Gottlob Werner, a German geologist of the 18^th century who instructed at the Freiburg Mining Academy in Saxony. He was considered a competent mineralogist by his peers and students, and his scheme for identifying minerals and ores was pervasive throughout the industry in Europe. Central to Werner's own work was his interpretation of the geologic history of the Earth. His treatise outlined how all rocks of the Earth's crust were mostly of marine origin, deposited or precipitated from a worldwide ocean that once enveloped the entire planet. Sounds like that awful Kevin Costner movie. Certainly many sedimentary rocks are of marine origin, but others are definitely not formed in any way by water. Anyways, Werner's envisioned planetary ocean was placed in Deep Time's Archean (which wasn't yet conceived, but for simplicity's sake lets say Werner placed it in the oldest eon) and characterized as a hot, scalding primordial soup that was saturated with all the dissolved minerals needed to form the basement rocks (Urgebirge), essentially the igneous & metamorphic cores of mountain ranges, cratons, and platform bases.


Abraham Gottlob Werner circa 1800

Werner's interpretation continued into the next phase with the onset of subsidence and cooling of the old ocean. This phase was marked by the deposition of consolidated, stratified, and fossiliferous sedimentary strata that was structurally deformed in many places. The fossils, he said, proved the planet had become suitable for life, and indeed this may have been an early explanation for the Cambrian explosion of the early Paleozoic era. Above these rocks layers was what Werner called Flotzgebirge, a term used to explain formations and groups of sandstones, shales, coal beds, limestones, and even basalt. But therein lies the problem we can all identify, using our 200 years of compounded knowledge and in situ studies.

So although initially received with great interest and enthusiasm, Werner's ideas soon drew criticism for failing not only to properly explain many features of plutonic & volcanic origin (see below), but what had become of the immense volume of water that once covered the Earth to a depth so great that all continents were totally inundated. The amount locked in continental & alpine glaciers in the late 1700's was not sufficient explanation, given knowledge of the cryosphere in the 18^th century, and the topography of the ocean floor was barely mapped (it wouldn't explain it anyways). Neptunism had to pooh-pooh anything to do with volcanism, and some of the ideas bandied about were absurd even for the day. I once read that volcanoes were vents for the expulsion of burning plant matter (coal) from within the Earth; essentially they were labeled by Neptunists as cone-shaped barbecues.

Various volcanic features and forms,
most of which were unexplained or
dismissed by Neptunists

As the 18^th century drew to a close, criticism of Neptunism strengthened with visible and indisputable field evidence for the counterargument of Plutonism. Geologists, especially ones investigating volcanic complexes in France's Massif Central (Nicolas Desmarest, Alexander von Humboldt, Rudolph Eric Raspe), were able to clearly demonstrate volcanic origins for basaltic layers and various features such as cross-cutting dykes, sills, tephra layers and structures (*wink* like Pumice Castle *wink*). Geologists who conducted these field studies formulated an opposing view, and came to be the Plutonists. According to the Plutonists, fire was the key to the origin of igneous rocks such as basalt, not precipitated minerals from a marine environment. James Hutton, considered one of the fathers of early geology, was an advocate for Plutonism who stated that classical igneous rocks such as basalt and granite “formed in the bowels of the Earth from melted matter poured into rents and openings in the strata”. Hutton's Uniformitarianism concept also espoused how the agents of deposition and erosion at work in the present have been working since the beginning of the Earth. The Neptunist vs Plutonist debate thus became amplified in the later Uniformitarianism vs Catastrophism debate, with many of the same hypotheses being refined and carried over. I wonder how much the spirit of those old arguments carried into the Geosyncline vs Plate Tectonic debate.

Debate is good for the evolution of a scientific discipline, and though today's debates in geological academia are of a different flavor than the one I've just focused this post on, they are just as important in furthering our understanding of the spheres of our natural world, an understanding that I hope never comes to a completion. If anyone wants to check out some quoted material from early Plutonists, look no further than this page which has explanations of fractionation & igneous differentiation by English geologist George Poulett Scroupe.

Additional Info:

It's Cold and Loud Up There

2011-01-06T17:56:00.001-08:00

My country's weather network occasionally shows vignettes about weather trivia, and one of them furrowed the brow of my sweetheart when she heard it, and truth be told it threw me off a bit as well.

The coldest temperature ever recorded in Canada was on February 2, 1947 in Snag, Yukon. The air temperature was -63°C. The air was so cold that meteorologists in the area could hear voices from 6 kilometers away.

This lead to questions of whether sound waves can travel further in cold or warm air masses, all else being equal. So I, with my limited physics and more thorough atmospheric science knowledge take a stab at the inquiry.

Google Earth snapshot of Snag area (62° 23.954'N 140° 22.302'W)
Nearest significant hills are 15+km north

It might sound counter-intuitive, but if sound travels faster it does not also travel further. Within warmer air masses, molecules are moving (vibrating) more rapidly, and thus the propagation of sound waves, which move via molecular collision, is quicker. However, as the molecules of air in a warmer air mass are further apart due to expansion, attenuation of sound waves will occur, and thus the intensity (decibel) of the sound will diminish compared to a colder air mass. Essentially warmer air is "stiffer", not as “elastic” as colder air due to the molecules moving around with more energy.

Density is the key for the propagation of sound, and as we all know a cold air mass is denser, with more tightly packed molecules. Under those conditions, attenuation is not as pronounced, and sound waves collide molecule-molecule with ease. But these are simply the basic conditions for sound in the atmosphere, and a Chicago meteorologist explains the key factor best:

The most important factor, though, is the great difference in the thermal structure of the lower atmosphere when it is cold versus when it is hot. When air temperatures change along the path that sound waves are traveling, the waves always bend toward the colder air. In bitterly cold arctic air masses, the coldest temperatures are at the ground with higher temperatures above; sound waves do not disburse upward readily. On hot days, it's just the opposite: It's hottest at the ground and cooler above; sound waves bend up and away.

Certainly to get a -63°C temperature requires a bitterly cold arctic air mass, and early February is deep within winter, where the snow cover is widespread and the positive feedback of constant reflective albedo has had plenty of time to cool down the region. The nearest major town with historical records from Environment Canada is Burwash Landing, and Burwash shows a February daily minimum average of -25°C, with an extreme of -55°C recorded in 1968. This highlights an extreme diurnal temperature range due to continentality. The Gulf of Alaska is ~300km away, but High pressure Arctic anticyclones (cA) sweeping down from the Beaufort Sea (which is equivalent to a white landmass) ~800km away, prevail over any weak westerlies from the northeast Pacific. The February polar jet stream is far below Snag.

I hope this clears up the same question anyone else might have about air temperature and how sound carries. Inevitably other factors, such as wind direction/speed, topography, and humidity come into play and add complexity. Back on that mighty cold day, the meteorologists also made mention that they could hear their breath freezing just after exhaling. Be careful not to shout in -63°C, or you might break your foot.

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On the Geology & Topography of Herefs

2011-01-03T09:43:00.001-08:00

Last summer my experience at university took an interesting turn, as I was recommended to a couple of professors to be taken on as a research assistant. The work primarily involves GIS mapping with ArcGIS. I jumped at the opportunity to get involved in academic research in the realm of geography, and the flexibility it offered fit around my existing work and studies quite well. I'm a bit of a workaholic, and not a procrastinator (does that word have an antonym?), and I think that came as a surprise to my new bosses.

One of my bosses doctoral research involves various counties of England and their historical land ownership issues. The work that is thrown my way generally involves spatial analysis of locations and distances within these counties, and I've relished learning the specific geography of each. So far focus has been on the Southwest, but the most recent county I've examined is Herefordshire in the west midlands. I use Google Earth to gather location elevation data, and when perusing the county, I got a sense of its topography and land use. But that's not where a geonut would stop inquiring; we need to know why the topography is the way it is.

Many people (and by that I mean my narrow assumption) when they think of the countryside in England picture rolling green hills and a preponderance of farm plots, broken up occasionally by a Sanford Gloucestershire-type town. Herefordshire turned out to be pretty much that way, with a few breaks in the stereotype.

The Bedrock geology of Hereford is dominated by Devonian (416-360 Ma) Old Red Sandstone, a huge sedimentary rock series formed from the erosion & deposition of the ancient Caledonian mountains, which formed when Laurentia (North America) and Avalonia (British Isles + Northeast USA) and Baltica (Scandinavia + Eastern Europe) all collided together, forcing up an imposing mountain range. Over millions of years the Caledonians eroded, and deposited in basins at shoreline margins and across broad tropical plains (England was around the equator for much of the Paleozoic) was the eventual mudstone/sandstone material that would lithify into the ORS. Looking at the figure to the right, a lesser portion of Herefs bedrock is Silurian (444 - 416 Ma) limestones, sandstones and shales, mostly in the northwest & southeast. This Silurian system of sedimentary facies contains the greatest abundance of fossils in Herefs, with brachiopods, trilobites, and the more elusive graptolites. If one were to dissect the underlying strata, one would find an interweave of shales, conglomerates, mudstones, etc....basically a sedimentary rockcake, albeit slanted, slightly deformed, and with a few coal chips.

There are some unique igneous and metamorphic formations that protrude the landscape. Herefs portion of the Malvern Hills to the southeast are composed of Cambrian quartzite, and so are a few low-relief hills just outside Brampton Bryan, though it would be hard to view them unfettered due to fence-fence agricultural development. Quaternary glacial activity during the Pleistocene brought the bulldozing force of glaciers down to the county, frequently smoothing out and rounding the landscape during advances & retreats, and thus till mantles a fair number of the hills and broad uplands. Glacial erratics were left behind on top of some taller hill groups such as Hanter Hill and Stanner Rocks, both plutons. Chronological evidence of the furthest extent of glacial tongues ends 20 Ka, spreading into what is now the courses of the River's Lugg and Wye.

When I was perusing the southern half of Herefordshire, the most atypical feature that popped out is the River Wye gorge, and the community of Symond's Yat nestled around a bend in it. Here the river cuts a defile in Carboniferous limestone, exposing beautiful cliff faces, dissolved caverns that yielded fossils of deer, mammoth, and rhino analogues. All those features made the area appealing for tourism. Furthermore, the defile's profile reminded me of the Delaware Water Gap in the northeast US, mainly because the first geoposter I ever made had a section about the water gap. They have different geomorphological origins, but there is a resemblance in terms of limestone structure and general topography.

River Wye in southern Herefs (left) Delaware River in eastern Pennsylvania (right)

It would be a disservice to not mention the characteristics of Herefordshire's soil, which is given a red coloration by weathered Old Red Sandstone particles, making the pedon profile easily identifiable. The soil itself is primarily clay and/or marl. Five minutes on Google Earth in the county shows its multitude of farmland, and every type of use that the English are known for is found in Herefs (cattle, sheep, horse, hops, wheat, barley, turnips, fruit). Pear and Apple orchards dominate cultivated land in the county, ranking only second next to Devon in output; not surprising given Devon's larger area plus its portion of ORS. Man's love of drink means that all that fruit inevitably led to some local brews of cider becoming popular.

Herefordshire is definitive English countryside, and was part of the stomping grounds for the founding minds of geology. Indeed any keen geologist will recognize the significance of the old British tribes Silures & Ordovices and their proximity to the West midlands. Any input from locals of the region is particularly welcome. Next I might look into Devon, as it was the first county I did in-depth spatial analysis for, plus I have enjoyed a few of Dame Agatha Christie's novels set within it.

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The Pawn's First Move

2011-01-01T11:23:00.000-08:00

My first post on my new blog, and I guess introduction and purpose are in order.

As a geography/geology undergraduate that has completed his first two years, I feel confident (enough) in my gathered knowledge coupled with a bit of experience with the tools of the trade to start expressing myself more in written form. I hope the blog will not only tune me more towards consistent writing on earth science subject matters and experiences, but also act as a kind of archive of interesting topics I have come across in course studies, field journeys, scholarly papers, publications, and other earth science activities.

Indeed I wish I could continue endlessly taking courses, perpetually learning knew things about every sphere of the earth system, but more and more I find that intermixed with studies is practical application, be it my GIS work for professors, or volunteer work for environmental agencies, or personal exploration of unique geological sites in my neck of the woods.

What about the name? Really, it's because I had to choose something, and it had to be zippy. I have a distinctive interest in Oregon, as it is far enough from my home in BC to be exotic, but close enough to reach in a hard day of driving. The last time I was in the state, I explored central Oregon's semi-arid landscape, trekked around a shield volcano, walked on the lunar-like terrain of pyroclastic lava flows, gave myself a shock looking down a steep basalt canyon, and climbed up a mesa's fortress walls.

Pumice Castle itself is a result of its material toughness and foundation standing tall while deposits and lava flows around it eroded and fell into Crater Lake. Mazama is a composite volcano, its layers alternating between air fall deposits of ash/lapilli and lava flows of a basic to andestic/rhyolitic nature. One such layer of air fall was composed primarily of violently erupted pumice, that when deposited upon the flanks of Mazama was so hot that fragments welded together, and formed a lens roughly 50-60m thick. That pumice layer is underlain by a particularly dense andesite layer from a previous flow, thus providing a strong foundation for the lens to resist erosive forces. The eruption that eventually led to the pumice castle was itself not voluminous, but was fast and explosive in a shorter-than-average time period.

NPS diagram at the site

Thus after quieter activity prevailed (Crater Lake still has potentially active cinder cones, ie. Wizard island and other submerged ones), erosion overtook deposition, and as the edifice collapsed inwards, Pumice Castle remained standing as a protuberance that has itself eroded over time as the topography has reshaped.

I recommend Crater Lake as a definite on any North American geo-nut's bucket list, in particular the Rim drive and little side diversions to the Pinnacles (welded fumaroles), Phantom Ship (volcanic plug), Devil's Backbone (andesitic dyke) to name a few. If you're like me, music is your extra companion on fun drives, and my choice for central & south Oregon ended up being Pure Cult. There's nothing quite like driving through the desert scrub on a clear early autumn day whilst She Sells Sanctuary fills the ears.