Playing with Matches: Piecing Together the Geological Puzzle of the Sea-to-Sky Corridor

Standing atop the Malamute, a granitic whale breaching beside Highway 99 opposite the Stawamus Chief, Quest University geologist Steve Quane hectors our magnifying-lens-wielding group through a series of simple observations. First, we evaluate the Chief—its height, sheer face, overhangs and domed flanks; its colour, streaking, and conspicuous dike cutting top-to-bottom through the entire formation. Next we examine the smooth rock on which we stand, its polished surface swarmed by striations that look like fingernails dragged through warm butter.

 

Steve Quane, in the field. Garibaldi Lake. Photo: Leslie Anthony

by Leslie Anthony

When Quane asks what we think we’re looking at, the terms “volcano” and “glacier” crop up often. Clearly, many of us have already leapt ahead to the very essence of the “fire and ice” idea behind Dynamic Geology of the Sea-to-Sky Corridor, the adult-education course in which we’ve enrolled. The ever-smiling Quane, however, is having none of our brown-nosing.

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While it’s hard not to reach for what we imagine might be behind our observations, there’s a process that needs respecting. Quane now steps us through the reasoning scientists would use to draw conclusions, helping us self-deliver a likely geologic
script. It turns out that a glacier did, in fact, occupy this entire valley. A large one, over two kilometres high, meaning that the Chief—and the university campus, and the baby farm that is Squamish—were at one time deep beneath it.

 

Tim Emmett ice climbing the lava flow bowl of Brandywine Falls. Fire and Ice. Photo: Jimmy Martinello

As testament, the glacier’s terminal moraine now lies under the waters of Howe Sound as a reef at Porteau Cove. Representing the 150,000,000 year-old basement of the Coast Mountains, the Chief comprises molten rocks formed 20 kilometres below the
Earth’s crust, begging a singular question: how does something gestated so deeply get exposed on the surface? Three ways, says Quane: 1) pushed up from below by subduction, the same process that sparked neighbouring volcanoes like Black Tusk and Diamond Head, visible from where we stand; 2) revealed by glaciers and water eroding material from above, and; 3) with a little help from isostatic rebound (what land does once the weight of glaciers is removed).

 

Basalt columns near Highway 99. Photo: Leslie Anthony

What we come away with isn’t all deep-time dogma and geologic metric, but the decidedly old-school idea of observation versus interpretation. The former must come first: ten observations may lead to one conclusion, but an eleventh might change
that completely.

And while geologic conclusions stemming from these are unavoidable, I have another: it occurs to me that the corridor’s multifarious outdoor activities—skiing its peaks, sledding its icecaps, riding its rivers, climbing its faces, hiking and biking its trails, canyoneering, scuba diving and even wind-riding in Howe Sound, southernmost fjord in North America—all owe something to this unique interaction of volcanoes and glaciers.

“It turns out that a glacier did, in fact, occupy this entire valley. A large one, over two kilometres high, meaning that the Chief—and the university campus, and the baby farm that is Squamish—were at one time deep beneath it.”

 

The bits that make up the Coast Mountains originated in diverse locations around the globe that all, in a plate-tectonic, Rubik’s Cube kind of way, met along BC’s south coast. All this crustal pushing and shoving led both to the jagged peaks we recreate on, and the mineral wealth in the ground. In addition, the Juan de Fuca plate has been subducting here, pushing under the North American plate to form the Garibaldi Volcanic Belt, extension of the Cascade Volcanoes of the US Pacific Northwest. All of this while massive Pleistocene glaciers swept back and forth across the land for millions of years. Basically, a lot went on here, meaning there’s plenty to learn.

 

Wedgemount Lake. Photo: Jimmy Martinello

We head north to the Tantalus Range overlook, scanning for evidence of glaciation. It can be seen in hanging valleys (evidence of side glaciers that fed the main valley glacier), recently de-glaciated faces and hills scoured round by glaciers, as well as in current glaciers, with their bergschrunds, crevasse fields, hanging icefields, and moraines. It is possible even to divine the level to which previous ice has risen by nunataks—peaks that once poked up from the ice sheet.

Then it’s on to Brandywine Falls, which offers a rare cross-section through 5–8 lava flows (no one’s sure exactly how many). The upper flow’s edge had a small V-notch in it that was cut back by a flood of water from under the receding valley glacier. At one point in time, water poured over all sides of the punchbowl now occupied by the falls. Evidence of a large, prolonged flood event is seen in chunks of water-worn basalt resting in the woods and by the trail.

Just south of Whistler, we inspect roadside columnar basalt. The hexagonal pillars form smallish monoliths on the east side which, in winter, capped in snow, resemble odd cupcakes. Up close you can see where columns have been bent sideways, clearly forming in a way that differs from lava that spreads unimpeded across the land to cool, as in Hawaii and Iceland. These lone hills sit atop a sinuous formation winding across the land from north to south, steep-sided and offering crazy views over Cheakamus Valley. The story: this lava erupted and flowed beneath a valley glacier, likely in meltwater channels or caverns created by earlier flows, accounting for the columns that look like they were forced into spaces.

 

Stawamus Chief granite. Photo: Jimmy Martinello

Though we don’t venture that far, there’s also Mount Meager to consider, a volcanic massif 50 kilometres upriver from Pemberton. Some 2,400 years ago, Meager uncorked one of Canada’s largest explosions, triggering a huge landslide and sending ash as far as Alberta. Though it hasn’t erupted in millennia, that doesn’t mean it won’t. In August 2010, a heat-mediated collapse of Meager’s Capricorn Glacier sent the largest slide in Canadian history—48,500,000 m3 of debris—thundering primarily fed by the Sphinx and Sentinel Glaciers, its outflow mostly restricted to subterranean seepage along the contact where lava dam meets bedrock. Reappearing as a handful of springs at the Barrier’s base, the water coalesces into Rubble Creek, which flows quickly to the Cheakamus. Quane explains this mid-hike as we take a break on a rock balcony overlooking the Barrier—a visage of untrustworthy entropy. Rock tumbles continuously from the intimidating face to talus below, and evidence of larger-volume rockfall is everywhere—including the infamous 1855–1856 landslides in which some 30,000,000 m3 of rock peeled off to form the boulder field for which Rubble Creek is named. Inherent instability and further risks from volcanic, tectonic, or rainfall activity prompted the province to declare the area below the Barrier unsafe in 1981, forcing relocation of a small village on Lucille Lake. Should the Barrier collapse to bring Garibaldi Lake down with it, damage would be catastrophic. Released in its entirety, the lake’s 1.29 billion m3 volume—that’s 1.29 trillion litresized water bottles—would see a 120-metre-high wall of water descend with 200 times the energy of the Hiroshima bomb to obliterate Squamish, creating an impact-wave in Howe Sound. Numbers like this were good reason to get a handle on the lake’s hydrology.

“The Juan de Fuca plate has been subducting here, pushing under the North American plate to form the Garibaldi Volcanic Belt, extension of the Cascade Volcanoes of the US Pacific Northwest.”

To identify the dam’s weak points, and stresses these might be vulnerable to, Quane has skied in to bore holes through winter ice to check temperatures, sonar-mapped the lake bottom from a boat, and measured outflow. At aptly named Overflow Creek, a surface drainage channel that runs only during spring snowmelt, Quane installed a digital stream gauge that logs water temperature and height every hour. We reach it after creeping across metre-deep snow barely solid enough to support us. The water’s weight on the logger measures stream level, weight that must be compensated for by barometric pressure readings from another instrument nearby. Quane retrieves both and downloads the data onto a small laptop, pointing to outflow spikes associated with large autumn rain events—precisely what he’s after.

 

“The Barrier”, holding back what could become one of the biggest waterslides of all time. Photo: Gunter Marx

As we check a second logger further down the lake, Quane explains that earthquakes or gravitational failure from landslides and debris flows anywhere in the corridor are hazards to the unstable Barrier, but climate change effects that load the water system quicker—like earlier and higher melt rates, or big rain events—might also increase pressure at the rock interfaces.

Our final measurement, on the hike out, is a logger set in Rubble Creek below where it bubbles out from the Barrier. Scanning the area, however, Quane finds that the $500 logger is missing along with the large rock it was bolted to. Invoking the skills he imparted on our first meeting, we engage in some forensic geology that suggests a small rockslide and impact wave caused this and other changes we observe (later, scanning aerial photos and drone footage, Quane will conclude the event occurred sometime after March 9). This discovery makes the roar of water and shadows cast by the rock walls looming above that much eerier—even for a geologist.

In this dynamic region, we know collapse of the Barrier is a geological certainty, and though the probability of it happening in our lifetime is low, it doesn’t make standing there any easier. Fire and ice indeed

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