Glacier melt to redirect Alaska's Alsek River, endangering world-famous rafting route

Glacier melt to redirect Alaska’s Alsek River, endangering world-famous rafting route
The Alsek River as it meets Dry Bay, Alaska. Credit: Sam Beebe/Flickr

The Alsek River flows from the Yukon Territory in northern Canada to the Pacific Ocean, with its mouth right on the edge of Glacier Bay National Park in Alaska. On its course, the Alsek cuts through some of the wildest country in North America—glaciers plunge into bright blue water, mountains tower in distance, and grizzly bears hunt wild salmon along its wildflower-studded banks. This wilderness has made the Alsek host to one of the world's most renowned rafting routes, from the Yukon to the Gulf of Alaska. Today, the mighty glacier-fed Alsek River meets the Pacific Ocean in Dry Bay—but that could change in the near future.

"Everyone just assumes that's where that river goes," said geologist Michael Loso in an interview with GlacierHub. "But it could go somewhere else." For years, Loso, who is the National Park Services' principal glacier investigator for central and southeast Alaska, has suspected that the Alsek may be destined to shift course. In a recent paper in the journal Geomorphology, he collaborated with several scientists to demonstrate this point.

On the way to its terminus in Dry Bay, the river passes through Alsek Lake. To the southeast of Alsek Lake there is a second body of water, Grand Plateau Lake, that is not currently fed by the Alsek River. Between the two lakes is the Grand Plateau Glacier, which serves as a dam that keeps them from merging. The Grand Plateau Glacier has been shrinking slowly for decades, but recession has accelerated in the last decade, when at times it has retreated more than one kilometer a year.

Researchers have concluded that at the current rate of retreat, the merging of Alsek and Grand Plateau Lakes is inevitable. One key piece of evidence is the depth of the glacier. If the glacier were shallow, there could have been enough land in between the two lakes that they would remain dammed even if the glacier disappeared completely. Loso explained that this is not the case, saying "Radar data allowed us to demonstrate that the glacier's depth is such that when the ice is gone, there will be nothing to prevent the two lakes from connecting."

Loso and his co-authors predict that once the Grand Plateau Glacier has retreated to the point that it can no longer serve as a dam, gravity is likely to entice the Alsek River to abandon its current route and enter the Pacific by the much steeper route of Grand Plateau Lake. While shifting the course of an entire river is significant on its own, this particular shift includes several challenging logistical consequences.

"Presently, the main recreational activity that takes place on the Alsek River is rafting. When people raft from Canada into Alaska, they end the trip in Dry Bay," explained Loso. "If the river moves to the other outlet it will actually move into the boundaries of Glacier Bay National Park." This will pose some significant challenges, as the part of the park that includes the new outlet is designated as National Park Wilderness.

When rafters finish the route trip today, they end up in a part of Alaska not connected to the road system. At Dry Bay there is an air strip, meaning that voyagers can easily be picked up by plane or helicopter. At the new outlet, there is no air strip and current regulations prohibit the building of such a structure.

The National Park is supportive of rafting, but the process to allow pick-ups would not be simple. "The National Park Service would have to figure out how to get people out of there and potentially modify some regulations," said Loso. "This is possible, but not trivial—it would take some advance planning and effort, and there would have to be a public process. It would be complicated."

In addition to rafting, there is also a small, but thriving, commercial salmon fishery at Dry Bay. If the Alsek abandons Dry Bay, so will the bulk of the salmon that traverse the river. Loso explained that the fishery likely would not be able to continue. "That fishery has been dealing with declining fish numbers for some time anyway," he said. "It would probably become economically impractical to continue a commercial fishery there without the main flow of the Alsek there to support these fish populations."

Joel Hibbard, who owns Canadian River Expeditions, a company that leads rafting expeditions on the Alsek, shares Loso's concerns. "Our guests travel from around the globe to see the ecosystems supported by the cold clean water that these provide," said Hibbard in an interview with GlacierHub. "This change would compromise a crucial component of how we, and the fishing community at Dry Bay, do business."

The people who depend on the Alsek River don't have long to establish contingency plans. Loso estimates that the shift of the Alsek will happen within 10-30 years, and possibly within the next decade. "The uncertainty is because of calving," explained Loso. "Because this glacier terminates in two different lakes, it loses a lot of ice to icebergs calving off into the lakes. It is much more difficult to predict the timing of calving than the timing of melt."

Hibbard hopes that the projected shift of the Alsek River will inspire people around the world to carefully consider the implications of climate change. "There is hope that this dynamic event will draw attention to the region and the challenges that climate change is presenting and, through that, help inspire people to visit and come to understand the scale of the change that is occurring," said Hibbard.

For now, rafting and fishing on the Alsek will continue, but in the future these industries may be another casualty of the climate crisis. With thoughtful preparation, the National Park Service may be able to work with rafting companies to ensure that visitors can be inspired by the Alsek River for years to come.

Hibbard and Loso both highlighted the importance of recreation on the Alsek, which appears to leave an indelible mark on those who visit it. "Life seems to stand still for a moment on Alsek Lake," said Hibbard, who described with enthusiasm the route he first traveled 17 years ago. "We do not know how this will play out," he continued. "But we can immediately begin asking tough questions of our political leaders and ensure we are planning for these changes now."


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More information: Michael G. Loso et al. Quo vadis, Alsek? Climate-driven glacier retreat may change the course of a major river outlet in southern Alaska, Geomorphology (2021). DOI: 10.1016/j.geomorph.2021.107701
Journal information: Geomorphology

This story is republished courtesy of Earth Institute, Columbia University http://blogs.ei.columbia.edu.

Citation: Glacier melt to redirect Alaska's Alsek River, endangering world-famous rafting route (2021, April 15) retrieved 6 May 2021 from https://phys.org/news/2021-04-glacier-redirect-alaska-alsek-river.html
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