June 30, 2011

Field photo Set #3

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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June 25, 2011

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

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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June 20, 2011

Kata Tjuta - the forgotten sibling

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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June 11, 2011

A new toy! Can I play?

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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    June 6, 2011

    Geology at a Birthday Party

    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.

    May 31, 2011

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

    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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      May 23, 2011

      Accretionary Wedge #34: That is Weird

      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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      May 17, 2011

      Field photo Set #3

      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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      May 13, 2011

      Looking through the archives: Melbourne's climate

      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.

      Click to

      May 9, 2011

      USGS and GIS

      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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        May 3, 2011

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

        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.

        Additional Info:

        May 1, 2011

        Columbia Basin Trip: Day 2 - Sisters along the Columbia

        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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