A devastating glacial lake outburst flood (GLOF) in India’s Sikkim region is offering stark lessons for Western Canada, where glacial retreat in the Rockies is creating new moraine-dammed lakes that could pose similar threats.
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A new study published in Science details how the collapse of a moraine dam at South Lhonak Lake in the Himalayas unleashed a surge of 50 million cubic metres of water, killing at least 55 people, leaving 74 missing and destroying the 1,200-megawatt Teesta III hydropower dam.
The event was triggered by thawing permafrost and climate-driven glacier melt, which expanded the lake and weakened its natural barriers.
“The Sikkim disaster was unusual because it wasn’t a typical landslide from a high rock face into a lake,” said Dan Shugar, a professor of earth sciences at the University of Calgary and co-author of the study.
“This was a failure of the moraine itself—the piles of glacial rubble left behind as ice retreats. The permafrost holding it together was thawing, and a section nearly a kilometre wide collapsed into the lake, triggering the flood.”
A moraine is an accumulation of glacial debris (soil and rock) that forms as a glacier moves across the landscape.
It is created by the erosion, transportation and deposition of material by the glacier.
Moraines vary in size and shape and are composed of a mixture of different-sized particles, from fine silt to large boulders.
Often, they form the walls of a lake, like earthen dams, filling as glaciers melt.
Shugar says the event highlights how sediment transport can intensify these disasters.
“We estimated about 15 million cubic metres of debris collapsed into the lake, but by the time the flood had surged downstream, it had eroded an additional 270 million cubic metres of sediment from the riverbanks,” he said.
“That’s what made the flood so destructive—it gained power as it moved.”
A warning for the Canadian Rockies
Scientists warn similar conditions are developing in the Canadian Rockies, where retreating glaciers are exposing unstable moraines and forming new lakes that could burst catastrophically.
Among the most closely watched is Peyto Glacier in Banff National Park.
Research led by Dr. John Pomeroy, a hydrologist at the University of Saskatchewan, has documented rapid glacier retreat in the area, with significant implications for downstream communities.
“Peyto Glacier has been in what we call a negative mass balance for decades, meaning it’s losing more ice than it gains,” Pomeroy said.
“But since 2021, after that extreme heat dome, it has been retreating at an alarming rate. It lost nearly 200 metres in a single year, and in the past five years, the glacier has shrunk by about 450 metres in length while thinning dramatically.”
Pomeroy warns Peyto Glacier has hit the point of no return and appears doomed to melt away, possibly within a decade.
“Glacier melt has a lag time to climate warming, and so this glacier is responding now to the warming that’s occurred over the last few decades,” he said.
“We had a snowy year a few years ago, and I thought, ‘Oh, this will turn it around,’ but nothing turns it around now.”
At the glacier’s terminus, a newly formed proglacial lake—provisionally named Lake Munro, after a scientist who spent decades researching it—is growing rapidly as icebergs calve off and melt from below.
The glacier has fragmented, with large sections collapsing.
“This is becoming an extremely unstable environment,” Pomeroy said.
“Huge chunks of ice as large as office buildings are breaking off. It’s becoming unsafe to work there.”
Pomeroy warns the collapse of such ice masses into the lake could trigger a GLOF similar to the Sikkim disaster.
What a glacial lake outburst flood could mean for Alberta
A sudden moraine failure at one of these lakes could send a surge of water and debris downstream, affecting Peyto Creek, Mistaya River and communities downstream.
Peyto Glacier drains northward into the North Saskatchewan River, so a GLOF there would not directly impact Banff or Lake Louise, but the floodwaters could still cause significant ecological damage, erode riverbanks and pose risks to infrastructure such as highways and bridges.
“The risk isn’t zero,” Shugar said.
“In the Coast Mountains, we had a similar event in 2020 at Bute Inlet, where a landslide into a glacial lake triggered a massive flood. While these aren’t annual events, they’re part of a broader pattern of increased geohazards as glaciers retreat.”
Overnight, between Aug. 9 and 10, 2012, a smaller-scale event at Mount Edith Cavell in Jasper National Park demonstrated the potential risks.
“A chunk of ice broke off into a glacial lake, creating a mini tsunami that flooded out the parking lot and trails,” Pomeroy said.
“It happened at 3 a.m., so no one was there, but if it had been during peaks or high tourism periods, it could have killed people.”
Mitigation and early warning efforts
In the Himalayas and the Andes, where GLOFs have caused mass casualties, governments have put in place early warning systems and mitigation strategies, such as controlled lake drainage and reinforced moraine dams.
“In Canada, we don’t typically have monitoring systems for these glacial lakes,” Pomeroy said.
“We (researchers) measure lake levels at Peyto, but government agencies aren’t systematically tracking these risks.”
Shugar says hazard assessments need to be updated regularly to reflect rapidly changing landscapes.
“These high mountain environments are shifting year by year. The hazards associated with them are evolving quickly, and we need to reassess risk accordingly,” he said.
Both researchers emphasize the role of climate change in accelerating these threats.
“If this same landslide had occurred 30 years ago, it wouldn’t have caused a flood—because the glacier was there,” Shugar said.
“The lake wouldn’t have existed. We’re rearranging landscapes, creating new hazards.”
Pomeroy points to broader consequences beyond floods.
“Glaciers act as water reservoirs, feeding our rivers during dry periods. Their disappearance will mean more erratic water supplies, impacting hydropower, irrigation and drinking water for millions,” he said.
Despite the challenges, Pomeroy remains optimistic.
“Humans are good water managers,” Pomeroy said.
“We’ll adapt. But we need to act now to monitor these lakes, assess risks and make policy decisions that acknowledge the changes happening in our mountains.”
