24 October 2022
The Barry Arm landslide in Alaska: increased rates of movement
On Friday the Alaska Division of Geological & Geophysical Surveys (DGGS) posted an update on the movement of the Barry Arm landslide. It provides strong guidance for people located on or close to the fjord in the vicinity of the landslide:-
- Due to the ongoing hazard, we ask people to exercise their best judgement and, where possible, limit travel in the Barry Arm area, including Harriman Fjord, Barry Arm, College Fjord, and upper Port Wells.
The Barry Arm landslide is a 500 million cubic metre landslide situated above Prince William Sound in Alaska. The Alaska DDGS has a quite detailed description of the landslide, which has been moving since at least 1957. However, one section is causing particular concern, as per this image:-
This section of the slope is known as the Kite, although adjacent areas to the right on the image are also actively moving. A very large rear scarp has formed at the crown of the Kite, as indicated by the arrow in the image.
On 16 September 2022, the DGGS reported that the landslide was moving at 40 to 70 mm per day. As the image above shows, the section that is active is located directly above the fjord. A major failure would likely trigger a displacement wave, although the size will depend on the volume of failure and the dynamics of the movement.
The landslide is located at 61.139, -148.169, and is clearly visible on Google Earth. There is much that is unknown, most notably the thickness of the moving mass. Unfortunately, access is currently restricted due to the risk associated with being on the water in the vicinity of the landslide.
Forecasting the likely future behaviour of large, unstable rock masses is very difficult. Loyal readers will remember the trials and tribulations faced by the monitoring team, and the local residents, of the Velsemannen rockslide in Norway, which repeatedly went through phases of accelerated movement that did not lead to failure. Indeed, in this case a large-scale collapse is not inevitable, but the risk is high.
The DGGS will post a further update on Friday “unless significant changes warrant earlier updates”.