A landslide near the glacier triggered the tsunami. Is there a climate link?

In 2020, Seismologists Goran Ekstrom Note that seismometers around the world detected a strange wobble on November 28.It came from a remote part of British Columbia’s steep, glacier-covered Central Coast Mountains, about 2,400 miles from Ekstrom’s office at Columbia University Lamont-Doherty Earth Observatoryin Palisades, NY

“When I find something [that] It looked a little weird, I looked more closely,” said Ekstrom, who studies unusual seismic events. Conventional earthquakes usually start with big, high-frequency shaking, but that’s not the case here. It’s more of a low-frequency rumble The sound, which gradually accelerates and then fades out — the kind of signal produced by a major landslide, according to Ekström’s research. He emailed Marten Geertsema, a natural disaster expert for the B.C. government. Not seeing the news, Geertsema began scanning the area for recent satellite imagery, looking for signs of unrest, but found nothing at first.

Around the same time, pilots in British Columbia heard of an unusual amount of wood floating in the fjord. They flew in by helicopter. Flying up a fjord along a river, they saw countless felled trees and a vast new wasteland of gravel. Tracing along a side valley occupied by a stream called Elliot Creek, they found the source: new scars from a massive landslide. It hit the meltwater lake at the foot of the West Glenville Glacier, triggering a tsunami that destroyed everything downstream. Scientists quickly connected the dots.

in a New paper in the journal Geophysical Research Letters, Geertsema, Ekström, and colleagues describe the scale and impact of the landslide, as well as its possible causes—including the rapid decline of the West Glenville Glacier, which has retreated about 4 kilometers from its mid-19th-century position. This is just the latest event in global warming, where alpine glaciers are retreating rapidly and creating conditions ripe for such collapses.The document is accompanied by Spectacular Visual Interactive Features from Hakai Collegesome of whom contributed to this report.

The aftermath of the November 2020 Elliot Creek landslide and tsunami, looking upstream at landslide debris and West Glenville Glacier. In the 1960s, the glacier extended to where this photo was taken. (Brian Menounos/University of Northern British Columbia)

Since 1900, at least 1,000 so-called glacial eruption floods have been known worldwide. They have killed at least 12,500 people and destroyed dams, towns, farms and wildlife habitat. Many occur in steep areas of the Himalayas; mountainous British Columbia and southeastern Alaska are also hotspots. While the reasons may be complex, rapid glacier retreat is a suspect in many cases. As the ice retreated from the narrow ice-carved valleys, the steep rock walls previously held back by the ice cracked open, barely hanging together. Often, meltwater lakes form at the toes of glaciers. All that’s left is time, precipitation, frost action and gravity.Therefore, many scientists believe that landslides and the resulting floods will increase as the climate warmsif they haven’t already done so.

The new paper is one of the most complete analyses of glacial eruption flooding to date. The authors, drawn from more than a dozen universities, government agencies and private research institutes, as well as the local Homalco and Xwe’malkwhu Aboriginal peoples, used laser mapping, satellite imagery, seismic data and state-of-the-art computer simulations to simulate what happened.

They concluded that some 50 million tons of rock — roughly the mass of all cars in Canada — fell 1,000 meters from the valley wall, into an unnamed meltwater lake at the tip of the glacier, and then into the glacier itself . Some ice may liquefy immediately, they said. Displaced water and sediment spewed about 100 meters and then washed down the 10-kilometer-long Elliott Valley at about 135 kilometers (84 miles) per hour, washing trees and soil. When it hit the adjoining Southgate River, the debris piled up in a huge fan; floodwater and debris continued through the river, creating a sediment plume more than 60 kilometers long in the downstream fjords.

No one was killed, but the outbreak destroyed large swathes of forest and salmon-spawning habitat on the traditional lands of the Homarko. Fisheries scientists believe that hundreds of thousands or even millions of fish have been completely killed, and the continued turbidity of the watershed could jeopardize their survival. A logging camp with more than a dozen vehicles was leveled, and fuel and hydraulic oil continued to leak from the wreckage. Like the locals, bears and eagles that depend on salmon could suffer long-term effects.

The paper says the immediate trigger for the landslide is not known, but the factors that lead to the landslide “include fractured bedrock with well-oriented joints and the first reinforcement of the slope bottom due to glacier retreat.” They describe the event as “in the An example of the sometimes underestimated chain of danger in high mountains experiencing rapid glacier melt. [Rapid] Retreat could increase the hazard of these events as the number and size of lakes increase beneath the potentially unstable slopes of alpine valleys. “

Ekström and his former Lamont-Doherty colleague Colin Stark began investigating the possibility of using seismic signals to detect​​​landslides around 2009. They have recorded more than 50 major events. The Elliot Creek slide isn’t even the biggest. In 2015, they detected 200 million tons of rock collapsing At the bottom of Tyndall Glacier in Alaska, under similar conditions.The following year, they discovered a 120 million tons collapsed Glacier Bay National Park in Alaska.

With the potential for increased damage, scientists are investigating the real-time use of seismic instruments to help authorities issue tsunami warnings and find victims.For example, the 2020 study led by Lamont-Doherty scientists looked at a slide from 1994 Seismic instruments detected Twenty-one people were killed just hours before the ensuing tsunami reached a village in Bhutan. People could have gotten away if the instruments had been hooked up to an early warning system. “It’s a startling and terrifying reminder, [outburst floods] Start at these high altitudes and gain devastating energy through gravity on the way downhill,” said George Shafferone of the study’s authors.

The researchers in the new paper say the close agreement between their physical models and the field evidence they collected could be used to help predict future outbreaks. “Fortunately, these and similar events in Western Canada are taking place in remote valleys,” they wrote. “However, given the development of these remote areas and increased tourism, there is no guarantee that this will be the case in the future.”