There is a giant rock that you can’t ignore along the famous Sea to Sky highway in British Columbia (B.C.), Canada, called “the Chief”. What’s pretty cool is it is actually a glacially exposed ancient magma chamber! The Chief is well known to the locals in Squamish, B.C., which was my home town. Thus, when I recently came back to Canada for the Geological Society of America (GSA) conference in Vancouver, I got to spend some time back home. Though I’ve hiked it many times growing up, I don’t think I’ve quite appreciated the awesomeness that is this giant granodiorite intrusion. And with a newly built gondola providing accessible views, I think this is a good time for a quick blog about the how this giant rock came to be, from its magmatic beginnings to its glaciated and carved present.
A glaciated volcanic heart
The Chief formed ~ 100 million years ago (mya) at depths of 15 to 30 kilometres beneath the earth’s surface. This was during a highly active period on the west coast of Canada that was subjected to scores of magmatic activity (plutonsim) (Rusmore & Woodworth, 1991; Monger & Journeay, 1993). These plutons are expressed as the beautiful mountains of the northwest coast of North America that range from B.C. through Yukon and Alaska (Monger et al., 1982). The Stawamus Chief (known as the Squamish Chief) crystallized slowly from a felsic igneous stock with a granodiorite composition (i.e. mostly consisting of the interlocking minerals of quartz, feldspar and biotite). It was intruded by multiple dark mafic dykes around ~ 40 mya.
How it came to be standing tall 700 m above the highway today is owe to the extensive glaciation history from 2.5 mya to 10,000 years ago. As glaciers advanced and retreated over the land they carved and plucked steep slabs off the face of The Chief. This plucking was synchronous with exfoliation weathering due to the expanding and cracking response of minerals and rocks at the surface which initial formed under higher temperatures and pressures.
The light patches on the face of the Chief (i.e. what the local’s call the “witch” or “face” in the Chief) is an example of recent slab breakage that exposed fresh (i.e. less-weathered), lighter coloured rocks.
Final thoughts
The Chief is a giant monolith that casts a shadow upon, and defines the town of, Squamish. Not only it is a impressive landmark with a newly accessible gondola and rock climbing meca, it also is a fantastic exposure of a giant rock with a neat geological history. What was once a slowly cooling magma chamber (possible the heart of an extinct volcano), is now exposed and towering over the town due to uplift, erosion and intense glaciation that took place on the West Coast of Canada. Hopefully its a reminder to all passing Sea to Sky drivers on the way to and from Vancouver/Whistler how awesome rocks are, and what an interesting place Squamish is to live… no bias from me of course…
-Stephanie
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Thank you for the simple description of the chief! Simply, I’ve tried reading scientific explanations but found only confusion. A question if I might… I’m reading a lot about Baja BC, any thoughts?
I’m wondering if you have opinions on Baja BC?
Thanks for a great explanation of how The Chief came to be. I think it’s a great balance of factual, geologic information presented in an accessible manner for people without a hard science based background.
Living in Vancouver around 2006/7, I randomly went for a drive with a friend to find somewhere new to eat. I thought I would surprise him by going up to Whistler but instead we were too hungry and stopped in Squamish. I can’t tell you what we had, the name of the restaurant, or anything else because we were across the road from “this crazy rock”, as I called it, like I had never seen before. I couldn’t stop looking at it with both fascination and a little shiver of fear.
I relocated not too long afterwards and have never managed to sneak away when I returning to visit friends in Vancouver. But I’ve never forgotten that night while we ate and I looked at this piece of the earth that seems so naked in comparison to the rest of anything I had seen. I knew enough to guess that something, a glacier or the earth shifting had scraped it clean and pushed it out in a rather short (geologically speaking) time frame.
Beyond that, I wanted to imagine something magical at the heart of it, because it somehow seemed to warrant that kind of veneration. Yet nothing seemed to fit until today. So with blanks filled in (and a little poetic license for good measure) my little adventure becomes the time we stole away and shared that magical dinner. where with love in their hearts the two boon companions sat in the lee of the great Chief, warmed by this heart of an ancient volcano until something sparked in their own, the gift of an ember of memory carried away in the night and keeping the three together as one, still to this day.
Hi Stephanie,
My 31 year old daughter is now based in Squamish and goes hiking around about when she can. This past weekend she went for a scramble up Co-Pilot. Somewhere en route she picked up a couple of rocks, from some scree on the way up as far as I can figure. She is a marine biologist and doesn’t know much about rocks, so she asked me – I used to be in geology but life changes and I haven’t been for a long while. Unfortunately the photos she sent aren’t that clear so I thought I would do an Internet search to try and find some detailed info on the geology around Squamish, and your blog popped up near the top of results! I will try the GSC/BC Geol Surv to see if there are any maps but I thought I would also ask you if you could tell me what Co-Pilot is made of, and if there are any mafic rocks around, as you note there are on the Chief.
Talking of the Chief, you note it is an ancient magma chamber. I don’t suppose you get close enough to it to see if there is vertical variability in crystal size and composition?
Anways, I will have to look at more of our blogs – they look very interesting!
Yours,
Stephen
Hi Stephen,
Thanks for the comment and reading my blog! I haven’t actually been up to Co-Pilot myself to see the rocks, but according to the geological maps it should be made of the Gambier Group (which early Cretaceous to late Cretaceous-aged rocks, dominantly mafic volcanics, but also some marine sediments). If you send me a photo perhaps I can help as well identify it more (my email is sykorastephanie@gmail.com). In regards to the Chief, I am not sure if a detailed study as been down to look at the variation in crystal size and composition on the either outcrop, but it would be neat if they did and there was something variation to see!
Cheers,
Stephanie
Interesting stuff! I’m not sure if you encourage questions but I was wondering what actual process uplifts these cooling magma chambers, anyways thanks for the read!
Questions are always encouraged! Process that led to uplift of magma chambers and mountains are the movement and intact of the earth’s tectonic plates (these are the rigid out layers of the earth known as the lithosphere). Overtime the pressure of plates colliding causes the land to be uplifted to higher levels. That is why we have exposures of things like the Chief at surface currently. I hope that helps, I talk about this in a bit more detail in my post on “How the Alps assembled; Mountain building 101” http://exploringthearth.com/2013/03/02/switzerland/ so definitely check it out if you are interested. Cheers!
Awesome thanks for the insight. I enjoyed going up on the gondola last time!
Thanks, Marina
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Haha, you’re welcome and thanks for reading 😉