May 14, 2020

A recently discovered unstable slope in Barry Arm could lead to a
landslide-generated tsunami
We, a group of scientists with expertise in climate change, landslides, and tsunami hazards, have
identified an unstable mountain slope above the toe of Barry Glacier in Barry Arm, 60 miles east of
Anchorage, that has the potential to fail and generate a tsunami. This tsunami could impact areas
frequented by tourists, fishing vessels, and hunters (potentially hundreds of people at one time). We
believe that it is possible that this landslide-generated tsunami will happen within the next year, and likely
within 20 years.

The slow-moving landslide we have identified along Barry Arm is well-defined by a band of terrain called a “scarp”
where the motion of the landslide has steepened the slope.

Landslides have set off giant waves elsewhere in Alaska and Greenland during the past decade. In Taan
Fiord (Icy Bay, Alaska), a landslide that began moving slowly decades ago suddenly failed in October
2015. The resulting tsunami reached elevations of 633 feet near the landslide, and 35 feet 15 miles away.
At Karrat Fiord, west Greenland, a landslide in June 2017 similarly produced a tsunami that killed four

 people and destroyed a large portion of the town of Nuugaatsiaq, 20 miles away. Surviving villagers still
have not returned because a nearby slope is deforming and threatening to fail. The unstable slope in Barry
Arm is much bigger than either of these examples, and thus has the potential to produce a larger tsunami
that could have impacts throughout Prince William Sound.
Slopes like this can change from slow creeping to a fast-moving landslide due to a number of possible
triggers. Often, heavy or prolonged rain is a factor. Earthquakes commonly trigger failures. Hot weather
that drives thawing of permafrost, snow, or glacier ice can also be a trigger. Commonly, large landslides
are preceded by rockfalls and other signs of increasing instability.
We have only preliminary results showing the potential spread of the tsunami. The effects would be
especially severe near where the landslide enters the water at the head of Barry Arm. Additionally, areas
of shallow water, or low-lying land near the shore, would be in danger even further from the source. A
minor failure may not produce significant impacts beyond the inner parts of the fiord, while a complete
failure could be destructive throughout Barry Arm, Harriman Fiord, and parts of Port Wells. Our initial
results show complex impacts further from the landslide than Barry Arm, with over 30 foot waves in
some distant bays, including Whittier. Field measurements and further analysis could allow us to make
these estimates more accurate and specific.

 The risk from tsunamis is especially high in Barry Arm and Harriman Fiord. Initial analysis suggests that a complete
failure of the slide mass would completely fill upper Barr Arm with debris, and generate a tsunami hundreds of feet tall
in outer Barry Arm and in Harriman Fiord. Beyond these confined water bodies the tsunami would still be likely to be
dangerous in shoals and onshore near the beach, but it would be unlikely to pose a hazard to vessels that are in
deeper water bodies. In the event of a complete failure of the unstable slope, the tsunami would have impacts well
beyond the bounds of this map.

What scientists need from local communities
The work that we have begun is meant to help those who visit or otherwise rely on the waters of Barry
Arm and Harriman Fiord - please let us know what we can do that best serves that goal. What specific
questions are most important to you? What could be done to reduce the danger to people who want to visit
or work in Barry Arm?

 Also, photographs or other documentation of what you have seen when you have been in Barry Arm,
including small rock-falls and landslides, will help us understand the hazard and may show evidence in
some change in the slope.

What we’re doing
We are working with the Alaska Department of Natural Resources, Division of Geological and
Geophysical Survey (DGGS), and have contacted the US Geological Survey to request their help to begin
monitoring as soon as possible. Ultimately we hope that our work would make it possible for the National
Tsunami Warning Center (NTWC) to monitor this landslide. The NTWC currently provides warnings for
earthquake-generated tsunamis, but does not have a mechanism for providing stand-alone
landslide-generated tsunami warnings. So far, the analysis of the Barry Arm landslide and tsunami has
relied on volunteer efforts and ongoing, funded studies that do not specifically target Barry Arm.

The slopes above Barry Arm, with Mt. Gannett in the background, have been photographed numerous times,
including in 1910, when there was no sign of glacial deformation. By 1957 the landslide had begun to move, leaving a
distinct scar on the hillside. Between 2009 and 2015 the slide moved further, leaving the larger scar visible in a photo
from 2019.

We conducted analyses using the photographs and measurements of elevation that were collected
previously from satellites and aircraft. By comparing successive images of the area, we can see that the
landslide moved 600 feet (185 m) down the slope between 2009 and 2015, at the same time as Barry
Glacier was retreating past the toe of the landslide. A preliminary analysis of satellite radar data from
2019 by Mylène Jacquemart, University of Colorado, suggests that parts of the slope are still moving,
albeit currently at much lower rates than in 2009-2015. We also examined the topography in order to
produce a preliminary estimate of how much rock is involved in the landslide.

 Glacial retreat in recent years follows a similar pattern to landslide motion, suggesting that the landslide was in part
supported by the glacier, and is shifting as that support is removed. This analysis was produced by Chunli Dai of The
Ohio State University, using Aster and Landsat satellite imagery.

Preliminary tsunami model simulations by Patrick Lynett, University of Southern California show a
tsunami reaching hundreds of feet in elevation along the shoreline in Barry Arm and Harriman Fiord. This
model assumes most of the landslide mass fails at once. The tsunami would propagate throughout Prince
William Sound, including into bays and fiords far from the source. The results suggest that there could be
a destructive tsunami in Whittier about 20 minutes after the landslide, reaching over 30 feet above the
tide. Valdez, Tatitlek, and Cordova could see noticeable waves of a few feet that are unlikely to impact
anyone onshore, but could produce dangerous currents at docks and in harbors. Chenega Bay appears
largely insulated from the tsunami, and no significant wave is expected outside Prince William Sound. It
is also possible that the landslide may result in a partial or gradual collapse, which would produce a less
severe tsunami, with impacts primarily within Barry Arm and Harriman Fiord. Considerable effort is
needed to maximize the accuracy of the tsunami model results, however based on testing of the model on
other tsunamis we expect that these preliminary simulations accurately reflect what might happen far
outside of Barry Arm and Harriman Fiord, assuming there is a complete or nearly complete failure of the
landslide mass. In other words, we believe these initial results are sufficiently detailed to support initial
assessment of the hazard faced in Prince William Sound.

 We have also compared this slope to other similar slopes in the glaciated mountains of coastal southern
Alaska, as a way of understanding if and when this failure might happen. Four sites are quite similar Lituya Bay, Taan Fiord, Grewingk Lake, and Tidal Inlet. Three of these have produced tsunamis that
reached hundreds of feet up nearby slopes, while Tidal Inlet has not failed, despite an obvious instability
in the slope and over 100 years since glacial retreat there. In the case of Taan Fiord and Grewingk Lake,
the landslide happened during the time when the glacier was retreating from the toe of the unstable slope.
Because the glacier in Lituya Bay retreated about 400 years ago, we don’t know what happened in the
first 150 years after retreat, but in the subsequent 250 years there were 5 or more large landslides and
associated tsunamis. These case histories provide a general picture showing that it’s common (at least half
of the four cases) for slope failures to happen at the same time as the glacier retreats. Barry Glacier is in
the process now of retreating away from the landslide toe, so it is plausible failure could happen any time.
If the slope doesn’t fail immediately, failure is still likely as time passes, as demonstrated by repeated
failures in Lituya Bay. However, it is also possible that the slope will eventually stabilize for centuries or
millennia.

The unstable slope in Barry Arm is larger than recent historic landslide-generated tsunamis, and perched higher on a
steeper slope than either the 1967 Grewingk or 2015 Taan landslides. The potential energy is approximately 10 times
greater than any of these previous events.

To inform and refine hazard mitigation efforts, we would like to pursue several lines of investigation:
Detect changes in the slope that might forewarn of a landslide, better understand what could trigger a
landslide,and refine tsunami model projections. By mapping the landslide and nearby terrain, both above
and below sea level, we can more accurately determine the basic physical dimensions of the landslide.
This can be paired with GPS and seismic measurements made over time to see how the slope responds to
changes in the glacier and to events like rainstorms and earthquakes. Field and satellite data can support
near-real time hazard monitoring, while computer models of landslide and tsunami scenarios can help
identify specific places that are most at risk.

 Letter signatories:
●
●
●
●
●
●
●
●
●
●
●
●
●
●

Dr. Chad Briggs; ​University of Alaska Anchorage;​ Anchorage, Alaska
Dr. Ronald Daanen, ​Alaska Division of Geological & Geophysical Surveys, ​Fairbanks, Alaska
Dr. Chunli Dai; ​The Ohio State University​; Columbus, Ohio
Dr. Anja Dufresne; ​RWTH Aachen University;​ Aachen, Germany
Dr. Jeffrey T. Freymueller; ​Department of Earth and Environmental Sciences, Michigan State
University​ ; East Lansing, Michigan
Dr. Marten Geertsema; ​BC Ministry of Forests, Lands, Natural Resource Operations and Rural
Development​; Prince George, British Columbia
Dr. Bretwood Higman; ​Ground Truth Alaska​; Seldovia, Alaska
Mylène Jacquemart; ​University of Colorado​; Boulder, Boulder, Colorado
Dr. Michele Koppes; ​Department of Geography, University of British Columbia​; Vancouver,
British Columbia
Dr. Anna Liljedahl; ​Woods Hole Research Center​; Homer, Alaska
Dr. Patrick Lynett; ​University of Southern California​; Los Angeles, California
Dr. Dmitry Nicolsky; ​University of Alaska Fairbanks​; Fairbanks, Alaska
Dr. Robert Weiss; ​Center for Coastal Studies,​ Virginia Tech; Blacksburg, Virginia
Dr. Gabriel J. Wolken; ​Alaska Division of Geological & Geophysical Surveys; Alaska Climate
Adaptation Science Center, University of Alaska Fairbanks​; Fairbanks, Alaska

Funding that support this effort:
●
●
●
●
●
●
●
●

NASA Earth Surface and Interior Program, award 80NSSC20K0491
Navigating the New Arctic, National Science Foundation, award 1927872
ArcticDEM supported by National Science Foundation awards 1614673, 1810976, 1542736,
1559691, 1043581, 1541332, 0753663, 1548562, 1238993 and NASA award NNX10AN61G.
Alaska Division of Geological and Geophysical Surveys
Alaska Climate Adaptation Science Center, University of Alaska Fairbanks
Coastlines & People: Stakeholder Education of Extreme Coastal Hazards, National Science
Foundation, award 1940351
An Immersive Coastal Hydrodynamic Simulation Environment, Office of Naval Research, award
N000141712878
NASA Earth and Space Science fellowship, award 80NSSC17K0391