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.

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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.

Additional Info:

• Super Natural BC - Princeton Hiking
• Archea (Fossil Huntress) - Fossils and Red Ochre 
• N.W.D Massey - Geological Compilation of the Similkameen Coal Basins, Southwestern BC: Tertiary Geology
  

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 read more...

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.

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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.

Additional Info:

• Oregon Explorer - Crater Lake Data Clearinghouse
• USGS - Mount Mazama and Crater Lake: Growth and Destruction of a Cascade Volcano
• USGS - Seafloor Mapping: Crater Lake shaded relief
• USGS - Merriam Cone Perspective View
• Charles Bacon et al. - Late Pleistocene granodiorite source for recycled zircon and phenocrysts in rhyodacite lava at Crater Lake, Oregon

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.

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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:

• Northwest Waterfall Survey - Latourell Falls
• Northwest Waterfall Survey - Multnomah Falls
• The Nature Conservancy - Tom McCall Preserve at Rowena
• Map of Oregon Waterfalls
• T.L. Barry et al - New 40Ar/39Ar dating of the Grande Ronde lavas: Implications for duration of flood basalt eruption episodes

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)

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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.


Additional Info:

• USGS - Columbia River Flood Basalts
• G. K. C. Clarke et al - Outburst floods from glacial Lake Missoula
• NOAA - Salt-wedge estuaries 
• Wind Energy Facilities in the Columbia River Gorge?

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

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)

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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

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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...

Additional Info:

• USGS Coordinate Info for Umtanum Ridge features
• David Alt - Glacial Lake Missoula and Its Humongous Floods
• J. D. MacDougall - Continental Flood Basalts (Petrology and Structural Geology)
• Floods, Faults, and Fire: Geological Field Trips in Washington State 

Learning from the gentry: Maars and Tuff Rings

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

Additional Info:

• Volker Lorenz - Maar-Diatreme Volcanoes, their Formation, and their Setting in Hard-rock or Soft-rock Environments
• Brennan T. Jordan - The Oregon High Lava Plains: Proof against a plume origin for Yellowstone?
• USGS - Maars and Tuff Cones
• J.D.L. White - Maar-diatreme volcanoes: A review
  

The Chief of a thousand

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?

Additional Info:

• Stawamus Chief Provincial Park
• Peaked out! Stawamus Chief geocache
• The Chief: Pillar of Granite