Submarine Deposition of a Subaerial Landslide in Taan Fiord, Alaska

Abstract

A large subaerial landslide entered Taan Fiord, Alaska, on 17 October 2015 producing a tsunami with runup to 193 m. We use LiDAR data to show the slide volume to be 76 + 3/−4 million cubic meters and that 51,000,000 m3 entered Taan Fiord. In 2016, we mapped the fjord with multibeam bathymetry and high‐resolution seismic data. Landslide and postlandslide deposits extend 6 km downfjord, are up to 70 ± 11 m thick, and have a total volume of ~147,000,000 m3. Seismic data image a blocky landslide unit and two units deposited immediately after the landslide. The blocky landslide unit is ~65,000,000 m3. We infer it consists dominantly of subaerially derived material and secondarily of fjord floor sediment. The overlying units are likely megaturbidites presumably deposited within minutes to days after the landslide. We infer that these deposits dominantly consist of fjord floor material mobilized and suspended as the slide entered and traveled downfjord. The lower postlandslide unit is up to 35 ± 6 m thick, and the upper unit is up to 12 ± 3 m thick. These deposits are distinctive and will leave a lasting record of the event. This subaerial‐to‐submarine landslide deposit is distinct from other submarine landslide deposits studied in Alaskan fjords because it has a much greater thickness, larger and more angular blocks, distinctive postlandslide megaturbidites, and a higher‐amplitude acoustic signature of the blocky deposit. The tight constraints on the landslide source and deposit volumes, topography, bathymetry, and tsunami runup heights and flow directions should make this a benchmark site for landslide‐tsunami models.

Karakoram geodetic glacier mass balances between 2008 and 2016: persistence of the anomaly and influence of a large rock avalanche on Siachen Glacier

“…In the case of the summer 2016 Aru twin glacier collapse (Kääb and others, 2018), the seismically inferred total mass was a factor of three to six lower than the avalanche deposit volumes derived from DEMs (see their supplementary text S10). Conversely, both methods agreed reasonably well on the total mass of rock mobilized (1-1.5 × 10 11 kg for the seismic method, 1.8 × 10 11 kg for the DEM differencing) during the 2015 Taan Fiord rock avalanche in the Gulf of Alaska (Haeussler and others, 2018;Higman and others, 2018). The seismic approach is thus efficient to precisely date the avalanche (Jiskoot, 2011), capture the sequence of events (Ekström and Stark, 2013) and locate them geographically (Higman and others, 2018) but needs to be combined with satellite imagery and DEMs for a more reliable estimate of the mass displacement.…”

A 36-Year Record of Rock Avalanches in the Saint Elias Mountains of Alaska, With Implications for Future Hazards

“…Several studies have documented landslides in the study area during the past century. Most recently, in October 2015 the Taan Fiord landslide (Dufresne et al, 2018;Haeussler et al, 2018;Higman et al, 2018) involved the collapse of 76 Mm 3 of material (Haeussler et al, 2018) from a previously identified, unstable mountain flank (Meigs and Sauber, 2000), onto the terminus of Tyndall Glacier and into Taan Fiord. This landslide generated a tsunami with a maximum onshore runup of 193 m (Higman et al, 2018).…”

Subaqueous mass movements in the context of observations of contemporary slope failure

“…understanding of the preconditioning factors, frequency and dynamics of these events is very important. In 2015 in Taan Fjord, Alaska, a 0.147 km 3 rockfall generated a large tsunami, fortunately with no casualties (Haeussler et al, 2018). The tsunami runup from this event was an astounding 193 m, making it among the largest ever recorded (Higman et al, 2018).…”

“…The tsunami runup from this event was an astounding 193 m, making it among the largest ever recorded (Higman et al, 2018). Post-event mapping has enabled a detailed calculation of the scale of the deposit, and the characteristics of the source area (Dufresne et al, 2018;Haeussler et al, 2018). It is likely that landslides in glaciated areas will become more frequent as the climate changes and glaciers retreat (Grämiger et al, 2017).…”