Fan deltas could preserve evidence of landslide-triggered tsunamis

The October 17, 2015, Taan Fiord landslide and tsunami generated a runup of 193 meters (633 feet), nearly an order of magnitude greater than most previously surveyed tsunamis. The tsunami changed the shape of several low-gradient fan deltas (fan-shaped piles of sediment shed from adjacent highlands) within Taan Fiord, making it an excellent laboratory for characterizing signatures of a landslide tsunami. A new publication documents those changes, some of which include complete vegetation loss over more than 0.6 square kilometer (about 0.2 square mile) of fan surfaces, formation of steep fan-front scarps up to 10 meters (33 feet) high, and formation of new tsunami return-flow channels. Two relatively stable fan deltas in Taan Fiord were heavily vegetated before the Taan event and may preserve features of tsunami modification for decades to centuries. Fans in poorly monitored regions, such as Greenland, could thus hold evidence of previously unidentified recent landslide tsunami events.

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