The retreating glacier presents the threat of landslides and the risk of tsunami in the Alaskan fjord

Using NASA satellite imagery and software processing approaches, a group of geoscientists have discovered a landslide-generated tsunami threat in Barry Arm, Alaska that is likely to affect tourists and locals in the surrounding area in the coming 20 years.

Barry Arm Glacier has declined rapidly over the past decade due to climate change, making the surrounding terrain unstable. The researchers found that the mountainside near the Barry Arm Glacier shifted 120 meters over the seven-year period between 2010 and 2017. Should that slow-moving landmass fail catastrophically, becoming what we normally think of as a landslide – would fall 3,000 feet into the fjord below, sending tsunami waves to neighboring communities.

The researchers jumped into action after the discovery, writing an open letter to community stakeholders. The results were published on October 29 in Geophysical Research Letters.

Chunli Dai, a geophysics researcher at Ohio State University in Columbus, worked with Bretwood Higman, geologist and co-founder of nonprofit Ground Truth Alaska, to analyze the slow landslide near the Barry Arm Glacier. Their team monitored the horizontal movement of the landslide using satellite imagery and measurements from the Landsat constellation of NASA-US Geological Survey, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Sentinel-1 of ESA (European Space Agency), Planet Labs and DigitalGlobe. As the longest-running Earth observation satellite program, Landsat provided the researchers with an archive of satellite images that allowed the team to see how the Arctic surface in that area has changed over time. Data from the Polar Geospatial Center’s ArcticDEM project was also used to measure the glacier’s elevation to see how its height has changed over the years.

Dai and his team developed new and innovative tools that confirmed the threat of the landslide near the Barry Arm Glacier. The instruments are sensitive enough to allow the team to detect signals associated with volcanic eruptions, surface changes due to melting permafrost and landslides. These tools select huge topographic datasets to detect subtle changes in the Earth’s surface over time, acting as a step towards better preparedness for the dangers in the evolving Arctic.

The new discovery arose from a large project studying the topography of the Arctic surface and how the landscape is changing. The project uses ArcticDEM digital elevation models and is funded by the NASA Earth Surface and Interior (ESI) program. This project intends to use high-resolution global topographic measurements so that NASA can better understand natural hazards and changing environments, said Benjamin Phillips, head of Earth’s surface and interior focus area at NASA. In partnership with the National Science Foundation, the National Geospatial-Intelligence Agency, and others, NASA supports the development and deployment of new digital surface models of the globe, built from optical images acquired from the DigitalGlobe constellation.

As the Barry Arm Glacier recedes, 600 million cubic meters of rugged terrain that was once supported by the glacier remains unstable. During a landslide, rocks and debris act less like a collection of solids and more like a fluid. In the event of a sudden subsidence of a landslide, this flow of rock and debris would likely fill the fjord, leaving several smaller lakes in place of the 450-foot-deep body of water.

Barry Arm Fjord and adjacent Harriman Fjord – 60 miles east of Anchorage on the south coast of Alaska – are popular with cruise ships, tour boats, fishing boats, kayaks and hikers. Due to the immediate dangers posed by the potential landslide and tsunami threat, Dai and the other scientists signed an open letter to local community stakeholders as soon as the hazard was identified, so they were aware of the implications the landslide is likely to have. generated a tsunami.

At the current elevation of the landslide, its mass would trigger a tsunami with waves hundreds of feet high at Barry Arm. The wider impacts of the tsunami include 30-foot waves hitting Whittier, Alaska. Prince William Sound could experience waves and current changes, and rocks and debris from the landslide would be scattered around this area.

If the landslide were to fail all at once, the potential energy stored in the event would be equivalent to a seven-magnitude earthquake, nearly ten times greater than any of the largest landslides that generated tsunamis in Alaska in the past 70 years, he said geoscientist Anna Liljedahl of Woods Hole Research Center in Homer, Alaska.

The resulting tsunami could travel up the opposite side of the fjord, damaging wildlife, hikers and vegetation. Further from the source, bays throughout Prince William Sound act as amplifiers, meaning that this tsunami would be less localized and more powerful even tens of miles from the source.

As a result of this discovery, the National Oceanic and Atmospheric Administration (NOAA), the agency responsible for tsunami warnings, is developing a preliminary tsunami model. In early June, NOAA also evaluated the fjord for wave height monitoring equipment, which could be installed and connected to their network of alarm systems by the end of the summer, said Liljedahl, who has worked with Dai to assess the Barry Arm landslide threat.

Alaska’s Division of Geological and Geophysical Surveys (DGGS) is also monitoring the Barry Arm region following the scientists’ discovery. They completed an in-flight lidar survey in mid-June to monitor the slide’s movement and are working with the Alaska Earthquake Center to install a seismic station near the fjord that will help detect sudden landslide movements. Without new monitoring equipment, Whittier would only have 20 minutes’ notice to evacuate should the Barry Arm landslide suddenly fail.

“There are many natural hazards that people in Alaska are used to: earthquakes, volcanoes and fire hazards. We have to take that mindset and apply it to the tsunamis generated by landslides,” Liljedahl said.

In addition to current monitoring efforts, geoscientist Bretwood Higman said having a GPS system on the landslide mass should be a top priority because it could provide a better indication of when the landslide will fail.

“Landslides sometimes accelerate just before they fail,” he said. “If you have a way to measure the deformation – if we see something like this – we can say that the risk is much higher right now, let’s take everyone out of the area.”

The movement of the landslide along the mountainside is strongly related to the retreat of the nearby Barry Arm glacier, as the surrounding area becomes destabilized as the glacier melts. While a tsunami generated by a landslide is not a certainty, knowledge of the risk informs the need to monitor and prepare for the possibility. “This is such a large area and a rare occurrence, but the risk of it happening is only increasing because we have this warm climate,” Liljedahl said.

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