The massive Kaskawulsh Glacier in northern Canada has retreated about a mile up its valley over the past century.

Last spring, its retreat triggered a geologic event at relatively breakneck speed. The toe of ice that was sending meltwater toward the Slims River and then north to the Bering Sea retreated so far that the water changed course, joining the Kaskawulsh River and flowing south toward the Gulf of Alaska.

This capture of one river’s flow by another, documented in a led by the 91̀½»¨ Tacoma and published April 17 in , is the first known case of “river piracy” in modern times.

“Geologists have seen river piracy, but nobody to our knowledge has documented it happening in our lifetimes,” said lead author , a geoscientist at the 91̀½»¨ Tacoma. “People had looked at the geological record — thousands or millions of years ago — not the 21st century, where it’s happening under our noses.”

, also known as stream capture, can happen due to tectonic motion of Earth’s crust, landslides, erosion or, in this case, a change in a glacial dam. The new study documents one of the less-anticipated shifts that can occur in a changing climate.

Shugar and co-authors at the University of Illinois and at Canada’s Simon Fraser University had planned fieldwork last summer on the Slims River, a geologically active system that feeds Kluane Lake in the Yukon. When they arrived in August, the . River gauges show an abrupt drop over four days from May 26 to 29, 2016.

By late summer, “there was barely any flow whatsoever. It was essentially a long, skinny lake,” Shugar said. “The water was somewhat treacherous to approach, because you’re walking on these old river sediments that were really goopy and would suck you in. And day by day we could see the water level dropping.”

The research team puzzled about what to do next. They got permission to use their mapping drone to create a detailed elevation model of the glacier tongue and headwater region. The resulting paper is a geological postmortem of the river’s disappearance.

“For the last 300 years, Slims River flowed out to the Bering Sea, and the smaller Kaskawulsh River flowed to the Gulf of Alaska. What we found was the glacial lake that fed Slims River had actually changed its outlet,” Shugar said. “A 30-meter (100-foot) canyon had been carved through the terminus of the glacier. Meltwater was flowing through that canyon from one lake into another glacial lake, almost like when you see champagne poured into glasses that are stacked in a pyramid.”

That second lake drains via the Kaskawulsh River in a different direction than the first. The situation is fairly unique, Shugar said, since the glacier’s toe was sitting on a geologic divide.

Clague began studying this glacier years ago for the Geological Survey of Canada. He observed that Kluane Lake, which is Yukon’s largest lake, had changed its water level by about 40 feet (12 meters) a few centuries ago. He concluded that the Slims River that feeds it had appeared as the glacier advanced, and a decade ago predicted the river would disappear again as the glacier retreated.

“The event is a bit idiosyncratic, given the peculiar geographic situation in which it happened, but in a broader sense it highlights the huge changes that glaciers are undergoing around the world due to climate change,” Clague said.

The geologic event has redrawn the local landscape. Slims River crosses the Alaska Highway, and its banks were a popular hiking route. Now that the riverbed is exposed, Dall sheep from Kluane National Park are making their way down to eat the fresh vegetation, venturing into territory where they can legally be hunted. With less water flowing in, did not refill last spring, and by summer 2016 was about 3 feet (1 meter) lower than ever recorded for that time of year. Waterfront land, which includes the small communities of Burwash Landing and Destruction Bay, is now farther from shore. As the lake level continues to drop researchers expect this will become an isolated lake cut off from any outflow.

On the other hand, the Alsek River, a popular whitewater rafting river that is a UNESCO world heritage site, was running higher last summer due to the addition of the Slims River’s water.

Shifts in sediment transport, lake chemistry, fish populations, wildlife behavior and other factors will continue to occur as the ecosystem adjusts to the new reality, Shugar said.

“So far, a lot of the scientific work surrounding glaciers and climate change has been focused on sea-level rise,” Shugar said. “Our study shows there may be other underappreciated, unanticipated effects of glacial retreat.”

The Kaskawulsh Glacier is retreating up the valley because of both readjustment after a cold period centuries ago, known as the , and warming due to greenhouse gases. A published in 2016 by 91̀½»¨co-author shows a 99.5 percent probability that this glacier’s retreat is showing the effects of modern climate change.

“I always point out to climate-change skeptics that Earth’s glaciers are becoming markedly smaller, and that can only happen in a warming climate,” Clague said.

Other co-authors are at the University of British Columbia, at the University of Colorado and at the University of Ottawa. The study was funded by the 91̀½»¨ Royalty Research Fund, Parks Canada, Yukon Geological Survey, the Natural Sciences and Engineering Research Council of Canada, the University of Ottawa and the University of Illinois.

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For more information, contact Shugar at dshugar@uw.edu or 253-692-4926 or Clague at jclague@sfu.ca or 778-782-4924.

More images are posted at .

A 91̀½»¨ Tacoma faculty member was part of an international team of scientists who worked with government agencies and private companies on a massive remote humanitarian effort after the earthquake. The effort is being this week in San Francisco at the American Geophysical Union’s Fall Meeting.

“This was one of the most rapid and largest global efforts to study a big disaster,” said co-presenter , an assistant professor at 91̀½»¨Tacoma. “Within days, satellites had been mobilized to acquire daily imagery of the earthquake-affected region, and provided data quickly to the scientific and citizen science communities. Teams of volunteers worked to map geohazards and damage to buildings and roads. This, to my knowledge, has never been done before at this scale.”

The humanitarian effort led to a of the landslides triggered by the Gorkha earthquake which is published today (Dec. 16) in the journal Science.

Lead author , a research scientist at the University of Arizona, brought his expertise in satellite imaging to help gather information after the Nepal earthquake, especially in remote mountain villages far from population centers.

Kargel called on colleagues in the (GLIMS) network he led to help identify affected areas by using satellite images. An international consortium of glaciologists, GLIMS monitors glaciers all over the world. The group’s initial efforts focused on possible earthquake effects on Himalayan glaciers, but quickly expanded to searching for post-earthquake landslides.

“The landslides don’t just happen immediately with the earthquake, they can continue for weeks or months afterward,” Shugar said. “People on the ground don’t necessarily know that a village is at risk of flood if a river is dammed far upstream. But when you have an eye in the sky, the people looking at that imagery might be the first to see it. We were looking for where there might be a risk in the next couple of days.”

Within a day or two, the scientists joined with the group to use remote sensing to help document the damage and identify areas of need, and share that information with international emergency-response teams and other groups.

Government space agencies and commercial entities, encompassing more than 10 satellites from four countries, responded to the scientists’ request to provide more data by sharing thousands of images. Kargel’s group selected which ones to analyze, and organized into six teams to scrutinize the vast earthquake-affected region for landslides.

Shugar led the team of volunteers focusing on the Annapurna region, in the westernmost part of the Himalayan region of interest.

“The shaking from an earthquake is like a tuning fork, where the tips of the fork — the mountaintops — vibrate the most strongly,” Shugar said. “This is why landslides tend to develop at the top of mountain ridges.”

Computer models were used to evaluate the likelihood that the downstream edges of glacial lakes would collapse to flood villages and valleys below.

Although the initial research effort was purely humanitarian, the scientists eventually realized they had a huge database that could be analyzed to learn more about geohazards from this and other earthquakes.

To study the Gorkha quake landslides, the scientists used their satellite-based findings plus media reports, eyewitness photography and field assessments from helicopters. The researchers limited their analyses from the day of the earthquake to June 10, 2015, the onset of the monsoon.

In addition to identifying the locations and severity of landslides, which was lower than expected, the researchers found a surprising pattern of where the landslides happened.

Co-author at NASA’s Jet Propulsion Laboratory used satellite radar imagery to create a map of the terrain that dropped during the earthquake and where land surface had risen. The Earth’s surface dropped almost 5 feet (1.4 m) in some places and rose as much as 5 feet (1.5 meters) in others.

By overlaying Fielding’s map with the landslide map, the scientists could see if there was any correspondence between the number of landslides and the Earth’s displacement. Most of the documented landslides occurred in areas where the ground surface dropped down, rather than in the areas where the ground was uplifted.

“Since this is the first time that this pattern has been observed, it’s tough to explain why it occurred,” Shugar said. “One of the things that we’ll be looking at going forward is seeing if there’s a similar pattern for other large earthquakes.”

Shugar recently joined 91̀½»¨Tacoma from the University of Victoria, Canada. His research focuses on landslide risk and steep slopes, but also includes glaciers, sea-level change and other geophysical phenomena.

“In Western North America we don’t tend to have communities living in steep mountain valleys in the way that they do in the Himalayas or the Andes, so the losses of life here would probably be less,” Shugar said. “But landslides are certainly a problem here, whether triggered by earthquakes or rainfall or some combination of those two elements.”

The Science paper’s three corresponding authors are Kargel, Shugar and of the University of Dayton in Ohio. Other co-authors include some 59 authors from 12 countries.

The research was supported by , Canada’s , the Japan Aerospace Exploration Agency (), Colorado-based , the and the Nepal-based (ICIMOD).

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For more information, contact Shugar at dshugar@uw.edu or 253-692-4926. Shugar participated in a in San Francisco and also related work in a .

This article was adapted from a University of Arizona . More images are posted .

Contact Kargel at Kargel@hwr.arizona.edu or 520-780-7759, Haritashya at uharitashya1@udayton.edu or 937-229-2939, and Fielding at Eric.J.Fielding@jpl.nasa.gov or 818-354-9305.