Fjord Delta Modification by a Massive Landslide Tsunami in Taan Fjord, AK
Abstract
On October 17th, 2015 a landslide adjacent to the tidewater Tyndall Glacier, located at the head of Taan Fjord in Alaska's Icy Bay, generated a massive tsunami that inundated and modified several large stream deltas within the fjord. Initial estimates of the maximum tsunami run up were as high as 150 m using the Alaska IfSAR-derived DEM. Before and after imagery from Landsat and GeoEye showed extensive vegetation loss up to 100 m elevation in places with indications that sediment had been redistributed or eroded from the deltas and delta fronts in Taan Fjord. The frequency of landslide tsunamis around the globe is poorly understood and identifying characteristic delta features in locations like Taan Fjord may reveal evidence of past events elsewhere. In the spring and summer of 2016 an interdisciplinary group of scientists travelled to Taan Fjord to conduct a post-tsunami survey that confirmed runup as high as 190 m and characterized the geomorphology and sedimentology of the fjord deltas using a combination of traditional and non-traditional methods. To characterize the sedimentology of tsunami deposits from this event, we dug individual trenches and trench transects on four deltas within Taan Fjord. The trenches revealed a relatively consistent stratigraphy on deltas both close to, and several kilometers from, the tsunami source. Ground penetrating radar surveys were completed between points on two transects to correlate and trace deposits between trenches. Several layers of poorly-sorted silt-starved sediment overlay a clearly identifiable substrate containing plant roots. To capture a detailed three-dimensional picture of geomorphic features on the deltas, pole-mounted and handheld structure-from-motion (SfM) surveys were conducted. Comparison of the SfM data to detailed topography of nearby unaffected deltas reveals characteristic dissimilarities between a typical fjord delta and a tsunami-inundated delta.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP41A0899B
- 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