A glacier that has been hanging onto an Alaskan slope for centuries is melting and facilitating what scientists call a slow-motion landslide. The soil is gradually being released from beneath the glacier and if this movement were to speed up, it could trigger a powerful tsunami.
The slope is located on the Barry Arm fjord on Prince William Sound in southeastern Alaska. A study led by Chunli Dai of The Ohio State University Byrd Polar and Climate Research Center estimates that from 2010 to 2017, the slope shifted by about 120 meters. “We are measuring this loss of land before the tsunami occurs,” said Dai.
Climate change is accelerating the pace at which glaciers are melting, and the ice loss can cause nearby slopes to become unstable. When the subsequent landslides dump massive amounts of dirt, rocks, and vegetation into a body of water, this can unleash a dangerous tsunami with no warning.
In the current study, the researchers found that if the entire slope on the Barry Arm fjord collapsed at once, tsunami waves could reach communities throughout the sound. These communities are home to hundreds of people, including fishermen, tourists, and members of an indigenous Alaskan group called the Chugach.
The researchers used satellite data to measure the size of the glacier that had covered the Barry Arm slope, as well as the amount of land that has already been displaced. Using these measurements, the team built models to identify the potential landslide risk.
The analysis revealed that from 1954 to 2006, Barry Glacier melted at a rate of less than a meter per year. After 2006, the rate of melting sped up so quickly that the glacier was thinning by about 40 meters per year. The glacier continued to retreat rapidly from 2010 to 2017, until the bottom point of the falling slope had butted against the glacier and became exposed to the water in Prince William Sound.
According to computer simulations, if the land along the slope collapsed at once, the resulting tsunami would send currents between 25 and 40 meters per second. This would be enough strength to cause significant damage to large cruise and cargo ships. Small fishing boats and kayaks, which frequent Prince William Sound, would be completely overwhelmed.
The study authors estimate that waves from the tsunami could reach 32 feet in the nearby town of Whittier. The tsunami could also disrupt fiber optic service to parts of Alaska, and release oil from the 1989 Exxon Valdez oil spill that is still contained in sediment in Prince William Sound.
The team noted that an earthquake, excessive rainfall, or snowmelt could easily trigger the landslide. “If the slope fails at once, it would be catastrophic,” said Dr. Bretwood Higman.
“People are working on early-detection warnings, so if a landslide happens, people in nearby communities might at least get a warning,” said Anna Liljedahl. “This kind of research might help with building those early-warning systems.”
The study is published in the journal Geophysical Research Letters.