AVO assists in multi-agency effort to monitor the Barry Arm Landslide in Prince William Sound

On February 9, under gray winter skies, AVO field technicians installed a 6-microphone infrasound array in Whittier, Alaska. While there are no volcanoes in Prince William Sound to worry about, AVO is using its expertise and experience with infrasound science to help with another hazard in Alaska: landslides.
You may be familiar with the large, intermittently-creeping landslide in Barry Arm, 30 miles northeast of Whittier, discovered in late spring 2020. There is concern that should this landslide rapidly fail into open water in front of the rapidly retreating Barry Glacier, a tsunami could threaten western Prince William Sound. A team of scientists and emergency managers from federal, state, and local agencies, in cooperation with academic scientists and community leaders, has been studying the situation and developing a monitoring system to aid in tsunami warning.

Tracking activity at a remote landslide such as this one is very challenging. Last year, the Alaska Earthquake Center installed two seismometers on and near the landslide, as well as a camera to watch for changes. Heavy snowfall has buried one of the stations and camera hampering data collection. This coming spring and summer, when conditions allow, more instrumentation is planned (by the National Tsunami Warning Center) to detect sudden changes in water level that indicates a wave has been generated.

In the meantime, AVO scientists suggested that an infrasound array nearby – on the road system in Whittier – might help detect large rock slides and falls or significant motion of the entire landslide block, activity that might mean the threat of tsunami has increased. Infrasound sensors listen for the low-frequency sounds (below what humans can hear) generated by a variety of processes such as volcanic explosions, avalanches, or rock falls. AVO uses this technique routinely to listen for explosions at Aleutian volcanoes. A signal from Barry Arm can be located using the geometry of the array sensors within minutes.
For more information on how infrasound is used at AVO, see https://avo.alaska.edu/about/infrasound.php
During its first days and weeks of operation, the infrasound array is detecting all sorts of noise in the Whittier area. AVO scientists are examining these data to determine the background ‘noise’ level, and tune the system to listen for potentially concerning sounds from Barry Arm. This technique is just one of several monitoring and detection tools being applied to help warn communities and mariners at risk.

For more information on the Barry Arm landslide, and to see the latest bi-weekly update on its status, see this web site managed by the Alaska Division of Geological and Geophysical Surveys:

AVO’s Wyatt Mayo digs through the snowpack to install an infrasound sensor in Whittier. USGS photo by C. Read, February 9, 2021.

Looking down into the snow pit where one of six infrasound sensors was installed at ground level on February 9, 2021. The pyramid shaped shield helps minimize wind noise. The conduit running from the sensor to the main power and data hub is at the top of the photo. Although the sensors can work if buried in snow, the signals will be attenuated as the snowpack consolidates, so periodic shoveling is required.

AVO technician Malcolm Herstand works on the main power and data hub for the infrasound array in Whittier. USGS photo by C. Read, February 9, 2021.