Barry Arm Landslide, Alaska: A New Tsunami Model Lowers the Worst-Case Wave

As Barry Glacier has retreated, the slopes above Barry Arm, a fjord off Prince William Sound in Alaska, have become unstable. A landslide there could slide rapidly into the fjord and set off a tsunami. A U.S. Geological Survey (USGS) report on the potential wave heights (Barnhart and others, 2021) found that the largest plausible wave is smaller than first estimated (Dai and others, 2020) — but still a serious hazard to people who live, work and play in Prince William Sound, who should stay informed and prepared.

Figure 1. The Barry Arm landslide and nearby towns, modified from Barnhart and others (2021). Base from the National Oceanic and Atmospheric Administration National Geophysical Data Center. Credit: U.S. Geological Survey.

What the new model shows

The landslide could creep downhill slowly or collapse rapidly into the fjord, pushing aside a huge volume of water. The researchers modelled several scenarios, but the rapid failure of the entire slide matters most because Whittier is so close.

• At Whittier, the worst-case waves could reach up to 2 meters (7 feet) just offshore — enough to cause severe property damage and endanger residents, though far less than the 9-meter (30-foot) wave estimated before. The wave could reach Whittier less than 20 minutes after the landslide.
• Closer to the slide, waves would be much higher. Heights depend on distance from the landslide and water depth, and are greatest in shallow water such as the heads of fjords. North of Point Doran in Barry Arm, modelled maximum heights exceed 20 meters (66 feet); in the southern part of Barry Arm and in Harriman Fiord, 5 to 20 meters (16 to 66 feet); in Port Wells and College Fiord, 2 to 5 meters (7 to 16 feet). Boats in these waters could face life-threatening waves with no time to get away.

The revised estimates rest on new, highly detailed maps of the landslide and seafloor made in 2021 by the Alaska Division of Geological and Geophysical Surveys (DGGS) and the National Oceanic and Atmospheric Administration (NOAA). Better maps let scientists model how the slide would displace seawater as it hits the fjord — the interaction that sets how high and fast the waves are. The slide will not necessarily fail quickly or all at once, but knowing the worst case is what preparation depends on.

What it means for residents

Although the maximum waves in Passage Canal are smaller than first thought, a rapid failure could still endanger Whittier and marine traffic across Prince William Sound. Residents should keep following officials' guidance on emergency planning, evacuation and marine safety, and may also want to:

• attend community meetings about the landslide and its tsunami hazard;
• put together an emergency supply kit and keep it within easy reach — the National Tsunami Warning Center lists what to include;
• check the ways they can receive tsunami and other weather alerts;
• practise an evacuation route with their household and rehearse a communication plan;
• read the guidance posted by DGGS and the other resources below.

Watching the slope

The USGS and its partners — DGGS, the National Tsunami Warning Center and the Alaska Earthquake Center — are working in and around Barry Arm to understand the landslide better and how a rapid entry into the fjord could create tsunami hazards. The team also plans an early warning system to alert officials and the public if the slope fails and a tsunami occurs, or if scientists see the landslide becoming more active. Residents may notice more helicopters and boats as scientists install and maintain monitoring equipment and survey the area. The USGS plans further updates through public meetings, reports, social media and briefings for local officials.

USGS scientists Brian Collins (left) and Jeff Coe (right) measure rock properties on the east side of Barry Arm. The type of rock and how broken down it is help in judging slope stability, and offer an analogue for spotting possible landslide hazards elsewhere. Credit: U.S. Geological Survey.

Where to find more

• Alaska Division of Geological and Geophysical Surveys — the most current information on the Barry Arm landslide, with links to partner agencies: https://dggs.alaska.gov/hazards/barry-arm-landslide.html
• Alaska Division of Homeland Security and Emergency Management — tsunami mitigation and community preparedness: https://www.ready.alaska.gov/Mitigation/Tsunamis
• NOAA's National Tsunami Warning Center — tsunami preparedness: https://tsunami.gov/
• NOAA's National Weather Service — current tsunami alerts: https://www.weather.gov/safety/tsunami-alerts
• Alaska Earthquake Center — earthquake preparedness: https://earthquake.alaska.edu
• The full report, Barnhart and others (2021): https://doi.org/10.3133/ofr20211071

Sources

Based on "New Model of the Barry Arm Landslide in Alaska Reveals Potential Tsunami Wave Heights of 2 Meters, Values Much Lower Than Previously Estimated," U.S. Geological Survey Fact Sheet 2022–3020 (May 2022), published by the U.S. Geological Survey; rewritten in hubnx's own words.

• The monitoring section, the resource list, the map and the photograph come from the fact sheet's PDF: https://pubs.usgs.gov/fs/2022/3020/fs20223020.pdf