On a day in mid-May, Quest University geologist Steve Quane and I are weighing the chances we'll have to don snowshoes on the 10-kilometre hike to Garibaldi Lake. Sitting at 1,470 metres, snowcover around the lake seems as indeterminate as a weather forecast that calls for maybe sun, maybe not, maybe even thunderstorms: we might not need snowshoes but... strapping the lightweight rigs to our packs seems prudent.
A dedicated trail runner, Quane sets a blistering upward pace. Though pressed to keep up, our fascinating conversation about his work overrides my protesting legs. Quane is studying the lake's —quite literal — ups and downs with a mind to natural hazards in a changing climate, and today we're ascending 800 metres to check on his remote data stations. "Hydrology is a fun new world of research I've never been involved in," enthuses the somewhat boyish scientist, whose usual investigations cover the how and why of volcanic landforms. This latest project doesn't stray far: hemmed by volcanoes, Garibaldi Lake owes its formation to just such processes.
Some 9,000 to 11,000 years ago, with the Cheakamus River valley still occupied by waning Pleistocene glaciers, lava flows from Clinker Peak on the west shoulder of Mount Price were halted by this ice, cooling hard against it. When the ice retreated, the lava front remained, a 300-metre cliff towering high above the Cheakamus; the backside of the kilometre-thick flow acted as a dam behind which meltwater pooled to form Garibaldi Lake — hence use of "The Barrier" to describe the formation. These days the 250-metre-deep lake is primarily fed by Sphinx and Sentinel Glaciers, with outflow over most of the year restricted to subterranean seepage along the contact where the lava dam meets bedrock. Reappearing as a handful of springs at The Barrier's base, this water immediately 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's—a visage of untrustworthy entropy.
Rock tumbles continuously from the intimidating face to talus slopes 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 from The Barrier to form the boulder field after which Rubble Creek is named. This inherent instability and potential 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. Rockslides are hazardous enough, but should The Barrier collapse and bring Garibaldi Lake down with it, damage would be catastrophic. The lake's volume is some 1.29 billion m3 —or, put in terms hikers can understand, 1.29 trillion litre-sized water bottles. If released in its entirety, a 120-metre-high wall of water would descend from 1,400 metres with 200 times the energy of the Hiroshima bomb, obliterating Squamish and creating an impact-wave in Howe Sound. Numbers like this are a good reason to get a handle on the lake's hydrology.
To identify the dam's weak points, stresses these might be vulnerable to, and how water might be involved, Quane has bored holes through winter ice to check temperatures, sonar-mapped the lake bottom from a boat, and measured outflow, both on Rubble Creek and through aptly named Overflow Creek, a surface drainage channel which runs only after spring snowmelt raises the lake level high enough. Here, a year ago, Quane installed a digital stream gauge that logs its temperature and height every hour. We reach it after creeping across metre-deep snow just barely solid enough to navigate without snowshoes. Suspended in a vertical PVC pipe, the water column'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. Pleased with the results, he points to outflow spikes associated with large autumn rain events — precisely what he's after.
"Earthquakes or gravitational failure from landslides and debris flows common in the corridor are hazards when it comes to The 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," explains Quane as we check a second logger further down the lake.
Our final measurement, on the hike out, will be a logger set in Rubble Creek just below where it bubbles from The Barrier. Bushwhacking, it takes a while, as Quane has made the path untraceable to the public, but eventually we find the site. Scanning the creek, however, Quane quickly realizes the $500 level logger is missing — along with the large rock it was bolted to. Speculative forensic geology suggests a small rockslide and impact wave caused this and other significant 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 rock walls looming above us that much more eerie — even for a geologist.
"Collapse of The Barrier is a geological certainty," says Quane. "But even though the probability of it happening in our lifetime is low, I don't like being down here."
Leslie Anthony is a Whistler-based author, editor, biologist and bon vivant who has never met a mountain he didn't like.
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