Tsunami threatening Prince William Sound

May 14, 2020

Credit Division of Geological and Geophysical Surveys

The threat of a large tsunami is looming in Prince William Sound, where a landslide could generate a wave with devastating effects on fishermen and others frequenting the area.

Geologists say that the rapid retreat of Barry Glacier from Barry Amy, 28 miles northeast of Whittier, could release millions of tons of rock into Harriman Fjord, triggering a tsunami that could rival or exceed the largest slide-caused tsunamis in the state’s recorded history.

The loose slope is on the western side of the arm, now bare and hanging at a precarious angle since the retreat of the glacier. Steve Masterman, director of the Division of Geological and Geophysical Surveys, says the slope could release 10 times the amount of rock as the two most noteworthy, slide-triggered tsunamis in Alaska history.

A landslide in Lituya Bay Fjord in Glacier Bay in 1958 generated a wave that went 1,700 feet up the opposite side of the fjord. The most recent major slide-caused tsunami in Alaska happened at the Taan Glacier in Southeast in 2015, where a wave went 600 feet up the opposite wall of the glacial valley.

Geologists estimate those slides were a fraction of what could come down in Barry Arm. A complete failure of the slope could fill upper Barry Arm with debris and generate a tsunami hundreds of feet tall in outer Barry Arm and Harriman Fiord. The tsunami could still be dangerous in Port Wells and farther into Prince William Sound, particularly in shoals and onshore near beaches.

The region attracts many commercial, sport, personal-use and subsistence fishermen, as well as recreational boaters, kayakers and campers. The Alaska Department of Fish and Game estimates that as many as 500 people may be in the area at one time.

Masterman says it’s not possible to predict a landslide with precision but geologists think it could happen within the next year — at least within the next 20. Factors like rainfall, snowfall and seismic activity could precipitate a landslide and the continuing glacial retreat increases the odds.

The DGGS is working with geologists at a number of scientific institutions and agencies to create better models to predict how large a tsunami might be and how it would move through the fjord and the entire sound.

In the meantime, the Alaska Department of Natural Resources and Fish and Game recommend avoiding Harriman Fjord and Barry Arm and nearby shoals and beaches until the hazards can be adequately understood.