Destabilization of glacial rock faces causes tsunami in alpine lake
When glaciers recede, the bedrock rebounds as the immense weight is removed. The rebound can destabilize cliffs and increase the frequency of rockfalls. A cliff collapse in the Héen Latinee Experimental Forest, Alaska, in 2016 highlights a poorly documented hazard associated with these dynamics. A 1,000-foot-high cliff surrounding a glacial cirque collapsed into the cirque lake, sending a tsunami 300 feet wide and 30 feet deep down the east fork of Cowee Creek. The wave scoured the stream channel to bedrock for about 2 miles and swept about 3,000 trees from the riparian zone into the channel. This event happened in a remote area where human populations and infrastructure where not affected, but rockfalls and landslides in similar terrains around the world have resulted in large loss of life and destruction of property. As glaciers recede in Alaska, the frequency of slope failures will increase, and given the number of lakes in alpine areas, alpine tsunamis will likely increase in frequency. Because the event happened within the Héen Latinee Experimental Forest, there are accurate data on the pre-event weather conditions and topography that allow for a well-resolved analysis of the conditions leading to the event and its impact on the stream channel and surrounding riparian zone. High impact/low frequency events are recognized as important in structuring stream habitats through inputs of sediment and large woody debris that create fish habitat. Documenting a previously unrecognized wood-recruitment mechanism increases our understanding of long-term habitat changes in the glacially influenced river on the Tongass National Forest.
Forest Service Partners