BC Volcanology 101 - Columnar Basalt

"Our volcanoes look like crap." 

-Dr. Kelly Russell (UBC), BC Magazine, Summer 2010.

       Having been born and raised in British Columbia and never having even considered the possibility that our province has a volcanic past until I began my degree in geology, I'm pretty inclined to agree with Dr. Russell on this point.

       Recently I got the opportunity to spend 3 days with some world-renowned volcanologists on a tour of the Canadian portion of the Cascade Volcanic arc (in particular the Garibaldi Volcanic Belt, or GVB) and it's formation during the Quaternary. The trip was put together by Dr. Graham Andrews of the California State University Bakersfield, and by Lucy Porrit and Dr. Kelly Russell himself, both from University of British Columbia. As a prelude to the Geological Society of America's annual meeting in Vancouver, the trip was one of many geologically-themed tours that anyone attending the conference could sign up for. Although expensive (but not one of the most expensive trips by far), this trip, for me was money well spent, indeed.

      Our trip began with an early morning meeting at the Vancouver Conference Centre, where I was introduced to fellow grad students from Canada and the USA, as well as our trip leaders and other enthusiastic participants!
      Our group also included a geoarcheologist, a planetary geologist, a veteren of the USGS in Hilo with his wife, a volcanologist from Japan who's English was limited, Professor Cathy Busby from UC Santa Barbara and Dr. Dave McGarvie from the Open University in Scotland - who I had been to see in the summer in Edinburgh to discuss various PhD projects in Iceland. Included in our crew was Dr. Volcano himself (aka Dougal Jerram): volcanologist and BBC presenter, he kept things light as we battled through torrential rain, delays, and various hiccups along the trip. After introductions, and an extra influx of caffeine, we loaded up our gear in the vans and headed of for volcanic rocks and a heck of a lot of BC rain!

       At our first stop en route to Pemberton along the Sea-to-Sky highway was at Porteau Cove, where we got the low-down on WHY our volcanoes in southwestern BC look like crap, exactly.
       First of all, to fill you in, BC is made up of several accreted geologic terranes that, due to many millions of year of subduction, have added themselves onto the ancient North American continent, creating the North American Cordillera - which itself ends approximately at the Rocky Mountains, and stretches northward creating the Yukon and portions of Alaska, and southward into the western United States.
       Quaternary volcanism in this region of BC is due to the subduction of the Juan de Fuca plate along the Cascadia Subduction Zone (CSZ), and the subduction that has taken place during the last 4 Ma is suggested to be responsible for uplift of the Coast and Insular Belts (terranes), including the GVB. There is evidence for a relatively hot seafloor being subducted: this creates a buoyant subducting plate and thus an uplift of the overlying continential column. As the GVB get's uplifting, mass wasting increases as erosion rates are accelerated, which, in short, gives this region it's "crappy" volcanic appearence - especially when related to Washington and California states beautiful, textbook stratovolcanoes (think Mount Baker, Mount Rainier, Mount Shasta, etc).

       The regional perspective of the geology now aside, and the rain beginning to set in, we were off to look at something that has fueled my desire to work in sub-glacial volcanology since I first saw it in the fall of 2012: Columnar Basalt. Our next stop was up along a forest service road west off the highway just past the Squamish Chief, and showed us the edge of the Mount Cayley volcanic field and the Tricouni lavas, which give evidence of lava-ice contact in the adjacent valley, and is demonstrated by spectacular radial columns (Fig. 1b). Kelly was determined that the rain would not shut us out, even though the weather was getting heavier by the minute, he busted out some magnets to attach geologic maps to the side of one of the UBC field vehicles (Fig 1a).

Figure 1a. Dr. Kelly Russell orients us at the Tricouni lavas,
with a spectacular slope of broken basalt columns in the background.

Figure 1b. Radial columns in the Tricouni
lavas, Dave McGarvie for scale (bottom left).

       We then continued northward along the highway and stopped to view spectacular road cuts that exposed some of the Cheakamus Valley lavas and a section of the basement rock (Fig 2a), which is highly metamorphosed. Although these flows show us beautiful columns (Fig. 2b), the vent or source of these lavas, as well as a basaltic dyke that may be a feeder dyke to this deposit, is not clear.

Figure 2a. Highly metamorphosed basement rock, overtop of which the Cheakamus lavas flowed.

Figure 2b. Dr. Volcano (Dougal Jerram, bottom right) for scale at
road cut, showing two flows with different column formation.

       Brandywine Falls (Fig. 3a) was our next stop, to investigate the outcrops along the BC Railway, and, of course, to oooh and ahh over the falls. Here, I also discovered what a hyaloclastite was, and why everyone had been talking about them on this trip! It was my first field-encounter with volcanic glass (Fig. 3b).

Figure 3a. Brandywine Falls, showing four different column layers.

Figure 3b. Hyaloclastite! A hydrated, tuff-like breccia that is found in subglacial eruptions, and full of volcanic glass (can you spot any of the black shards in these samples?)

      The last stop on day one was where I fell in love with columnar basalts, and I was excited to show Dave, my potential supervisor, exactly where I began my passion for subglacial volcanics. For you BC geologists, you've likely seen this site - the eastern portion of the abandoned Railway Quarry north of Squamish which, in the words of several volcanologists on our trip, is a "World-Class Outcrop". This portion of the Cheakamus Basalt lavas show all sorts of shapes of columns and change in size and orientation from the base of the outcrop to the top.
       In general, the joints of the columns form perpendicular to the flow. Columnar basalt and it's formation can get complicated and unclear very quickly, so please, enjoy the following photos (Fig 4a-e) instead of my attempt to deeply explain them here:

Figure 4a. Graham at an outcrop that demonstrates 'pinching' of columns toward the top of the flow.

Figure 4b - columns, galore!! 

Figure 4c - Columnar Basalt is always a hit with geologists!!

Figure 4d - Kelly, Dave, and Duncan (Lancaster University) examine column ends at an extraordinary outcrop.

Figure 4e - "World Class Outcrop" of columns! Apologizes for the lack of scale here... but isn't it cool??

Enough of Day One of our GSA trip - keep reading for more BC Volcanology in the posts to come, where we explore both the explosive AND effusive phase of the 2360BP Mount Meager eruption, as well as details on the massive Meager Creek Landslide from 2010.