Catastrophic Landscape Modification from Massive Landslide Tsunamis: An Example from Taan Fiord, Alaska

• Main Author: Bloom, Colin
• Format: Text
• Language: English
• Published: ScholarWorks@CWU 2017
• Subjects: Tsunami; Landslide; Icy Bay; Taan Fiord; Geology; Geomorphology; Greenland; Alaska
• Online Access: https://digitalcommons.cwu.edu/etd/636; https://digitalcommons.cwu.edu/cgi/viewcontent.cgi?article=1644&context=etd

The October 17th 2015 Taan landslide and tsunami generated a high runup of 192 m, nearly an order of magnitude greater than most previously surveyed tsunamis. Extensive modifications observed and documented on several low gradient fan deltas within the fiord make Taan Fiord an excellent laboratory for characterizing geomorphic signatures of a high runup tsunami event. Although interest in this topic is high, most prior post-tsunami surveys are from earthquake-generated tsunamis with relatively low runup, thus the geomorphic signatures of high runup tsunamis or their potential for preservation are uncharacterized. Additionally, clear modifications described during post-tsunami surveys are typically ephemeral and unlikely to be preserved. Geomorphic changes to Taan’s fan deltas included complete vegetation loss over more than 0.6 km2 of fan surfaces, formation of steep fan front scarps up to 7 m high, extensive local alterations of fan topography, and formation of new tsunami retreat channels. Two relatively stable fan deltas in Taan Fiord were heavily vegetated prior to the Taan event and may preserve features of tsunami modification for decades to centuries. If this is the case, fan deltas may be a previously unrecognized location for preservation of tsunami signatures on the decadal scale. As such, fans in poorly monitored regions, such as Greenland, could hold evidence of previously unidentified recent high runup events.