【環境科学】地すべりが引き起こす津波のリスクが氷河の融解によって高まる恐れ

The continued melting of mountain glaciers and thawing of permafrost in alpine regions could expose unstable hill slopes and increase the hazard of landslides that trigger tsunamis, according to a study in Scientific Reports.

As glaciers melt and retreat in a warming climate, they no longer support rock slopes which can lead to rock falls and avalanches. Glacial retreat also creates or extends bodies of water where tsunamis can form; along the coastlines of Alaska, Patagonia, Norway and Greenland, for example.

Bretwood Higman and colleagues report field observations of a landslide at the terminus of Tyndall Glacier on 17th October 2015, which sent 180 million tons of rock into Taan Fiord, Alaska, and triggered a tsunami. Although the landslide itself affected about 2km2 of land onshore, the tsunami affected over 20km2. Directly across the fjord from the landslide, the wave runup - the extent to which a wave rushes up on a beach or structure above the still water level - reached 193m. The authors show that the tsunami left a distinct sedimentary record, including deposits of wood fragments, soil and rock up to several meters thick that are very different from the typically sandy, thinner deposits of tectonic tsunamis. These deposits may be useful in identifying or interpreting similar events, including palaeotsunamis, in order to better understand their frequency and magnitude.

The observations reported in this study thus provide a benchmark for modelling landslide and tsunami hazards, and call attention to an indirect effect of climate change that may be increasing the frequency and magnitude of natural hazards near glaciated mountains.