Distinctive Sedimentary Record of a Landslide Generated Mega-tsunami, Taan Fjord, Alaska
Abstract
An approximately 100-m high landslide generated tsunami flooded the coastline of Taan Fiord in SW Alaska on October 17, 2015. Inundation reached 190 m at its highest point, and exceeded 50 m along over 10 km of coastline. Within the area of inundation, several alluvial fans provided both a source and depositional setting for sediment transported by the tsunami, and each fan is blanketed by tens of cm to meters of sediment. During a month of fieldwork in spring and summer of 2016, we sampled and documented these deposits. Where the wave was largest near the tsunami source, the deposit has two distinct layers: A) a basal layer with very poorly sorted sediment ranging from sand to boulders and B) an overlying layer composed of relatively well sorted cobbles and boulders where interstitial spaces are open except at the base of this layer, where they are packed with sand. Flattened vegetation at the base of layer A indicates the lower deposit formed during inrush. Channeling and small fan-like features in layer B suggest it formed during tsunami return flow. Farther towards the mouth of the fjord, where the tsunami was only a fraction of the initial height, two fans preserve a similar poorly sorted basal layer that was in many places overlain with boulders and/or sand. The thickness of the deposit and its consistency across multiple fans along the fjord suggest both that similar deposits could be indicators of paleo landslide-generated tsunamis, and that deposit stratigraphy from these kinds of events may record useful information about a tsunami's size and character.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP41A0900H
- Keywords:
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- 0799 General or miscellaneous;
- CRYOSPHEREDE: 1625 Geomorphology and weathering;
- GLOBAL CHANGEDE: 1824 Geomorphology: general;
- HYDROLOGYDE: 4321 Climate impact;
- NATURAL HAZARDS