12 September 2017
Increasing rock-avalanche size and mobility in Alaska
One of the most interesting landslide issues in recent years has been the cluster of rock avalanches that have occurred in the Glacier Bay National Park and Preserve in the southern part of Alaska (example include Lamplugh Glacier, Tyndall Glacier, Ferebee Glacier and Mount La Perouse). This area appears to have been affected by far more very large events than anywhere else over the last 20 years or so; the reasons for this have not been clear. In a new open access paper just published in the journal Landslides, Coe et al. (2017) have used Landsat imagery to map these events in the period between 1984 and 2016. Over this period this area experienced 24 rock avalanche events in a 5000 km² area, ranging from 5.5 km² to 22.2 km² in area. This map, from the paper, shows the distribution of these 24 rock avalanches:-
Some of these rock avalanches have been spectacular. This for example is a Planet Labs image of the July 2016 Lamplugh Glacier rock avalanche:-
From their mapping, Coe et al. (2017) concluded that all of the rock avalanches initiated from high mountain ridges or peaks. All occurred in the northern part of the study area, and most had an aspect towards the north, generally towards the northwest. Clusters in rock avalanche behaviour occurred in the periods 1984 to 1986; 1994 to 1995; and 2012 to the present. Notably, the most recent cluster has involved larger, more mobile rock avalanches than had been seen previously, and these landslides have tended to originate from higher elevations, with higher levels of mobility.
Coe et al. (2017) consider carefully why these changes may be occurring. They state that:
We hypothesize that degradation of rock permafrost is the primary factor that controlled the timing and size of rock avalanches in the Glacier Bay region.
This part of Alaska shows a clear warming trend over the last few decades. Coe et al. (2017) provide an analysis of the climate data that strongly supports the idea that the increasing temperatures may be leading to a degradation of previously permanently frozen rock masses in the high peak areas.
This is the most convincing evidence that I have seen to date that increasing temperatures are driving a higher rate of rock slope failure in high mountains, a trend that we also seem to be seeing in for example the Alps in Europe and the Southern Alps in New Zealand. It suggests that there is a pressing need for increased research into the processes occurring in high mountain slopes, including in situ monitoring. The implications are clear though – as climate change continues to drive warming in high mountain areas the risks associated with rock slope failure will increase.
Coe, J.A., Bessette-Kirton, E.K. & Geertsema, M. 2017. Increasing rock-avalanche size and mobility in Glacier Bay National Park and Preserve, Alaska detected from 1984 to 2016 Landsat imagery. Landslides https://doi.org/10.1007/s10346-017-0879-7
Planet Team (2017). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://api.planet.com