Alaska Lakes warns of “surprising” increase in rare threat

Alaska's lakes are experiencing a surprising increase in a rare threat that is now becoming more common as climate change worsens.

Lake tsunamis occur when landslides occur in small areas of water. Although typically only found in remote areas, they are becoming more common in areas with mountain glaciers such as Alaska and British Columbia. Ground Truth Alaska geologist Bretwood Higman recently warned at the Seismological Society of America (SSA) 2024 Annual Meeting in Anchorage, Alaska.

Maritime tsunamis are an “emerging climate-related threat,” Higman said. As temperatures warm, glaciers shrink, and if they are not there to support valley walls, landslides can occur. The warming climate is also causing permafrost to shrink, meaning the slopes above a lake are more likely to collapse, according to a summary of Higman's research.

Recent maritime tsunamis have occurred in Cowee Creek, Brabazon Range, and Upper Pedersen Lagoon, all in Alaska. These are very remote areas and probably unknown, but maritime tsunamis pose an increasing risk.

An active portion of instability on Portage Glacier overlooking Portage Lake, Alaska. This area is at risk from a lake tsunami in the future.

Bretwood Higman

Higman said it might not be long before a lake tsunami erupts in a more populated area. As an example, he cited Portage Lake near Whittier, Alaska, which is high on his list for a potentially destructive lake tsunami. Located in Alaska's Chugach National Forest, this glacial lake is just a few miles from Whittier.

Higman said more research is needed in areas like this to assess the risk. He added that analyzing seismic signals related to the landslides could cause the tsunamis.

“There are some cases where there are dramatic and very pronounced seismic precursor signals that precede a catastrophic landslide, sometimes by days,” Higman said in a statement.

“If we could get to the point where we understood these and knew how to recognize them, they could be really useful. This is something that has been a fairly rare occurrence in the past, but in recent years there have been really surprising numbers of them.”

There are other areas in Alaska that could be at risk of destructive maritime tsunamis due to their proximity to people and infrastructure. These areas include Eklutna, Seward, Valdez, Juneau, Grewingk Lake in Kachemak Bay State Park and Index Lake near Glacier View.

In 2020, a particularly large lake tsunami occurred in Elliot Creek, a glacial valley in British Columbia. According to a study by the University of Northern British Columbia, it was a 4.75 billion gallon landslide that caused a tsunami run-up of over 328 feet.

The tsunami was not dangerous to humans, but it damaged surrounding forests and salmon habitat. However, events like this are useful for scientists to prepare for more dangerous tsunamis in the future.

“There are places where we are seeing the same types of geologic instability that preceded these other events, but there are a lot of people at risk,” Higman said.

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