Landslides, tsunamis, and slope stability in Alaska

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Anja Dufresne

Senior Scientist

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+49 241 80 96779

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Landslides, tsunamis, and slope stability in Alaska

Project term: 2016 to 2020

 

At least 24 large rockslope failures occurred in Glacier Bay National Park in SE Alaska since 1984, our colleagues Coe et al. (2018) report. The resultant rock avalanches cover areas between 5.5 and 22.2 cubic kilometers. Two of these events are studied by research groups that Anja Dufresne from the Department of Engineering Geology is collaborating with.

 

The 2015 rock slope failure and tsunami in Icy Bay

rock slope failure Copyright: A. Dufresne Figure 1. On 17 October 2015, a landslide of roughly 180 million tons of rock landed on the toe of Tyndall Glacier and into the water of Taan Fiord. It sent a tsunami wave that reached as high as 193 m on the opposite valley slopes.

The October 2015 Tyndall Glacier rock avalanche caused one of the largest historic tsunamis in Alaska; maximum wave runup height measured from field evidence was 192 m (Haeussler et al. 2017; Dufresne et al. 2018; Higman et al. 2018). Located in the remote Taan Fiord, an arm of Icy Bay, no people or infrastructure were affected—nor would this event have been noticed if it hadn’t been recorded by the long-period seismic event detector at Lamont Doherty Earth Observatory of Columbia University in New York (cf. Ekström and Stark 2013). The slope it originated from has shown signs of deformation since at least 1996 (Meigs et al. 2006); its catastrophic failure in 2015 (Figure 1) released some 76 million cubic meters of rock, most of which now lies beneath fjord waters. Rapid response of a NSF-funded group of international researchers in the summer of 2016 gathered data which include bathymetry, aerial photographs, high resolution DEM, structural and sedimentological field data that, only a few months later, was already altered or destroyed by erosion, sedimentation, and/or advance of the glacier terminus (Dufresne et al. 2018).

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The 2016 supraglacial landslide on Lamplugh Glacier

landslide of the Lamplugh Glacier Copyright: A. Dufresne Figure 2. On 28 June 2016, a landslide initiated at a north-facing bedrock ridge and fell onto Lamplugh Glacier in Glacier Bay National Park and Preserve. The event was detected in seismic data at the Lamont Doherty Earth Observatory.

In June 2016, another event within the park made a media appearance: an estimated 46 million cubic meters of rock, ice and snow dropped approximately 1400 meters onto Lamplugh Glacier and deposited a spectacular rock avalanche of 10 kilometer length (Figure 2). It was first spotted by local pilots and also recorded at the Earth Observatory. Dr. Marten Geertsema of the Ministry of Forests, Lands and Natural Resource Operations (FLNRO), British Columbia, Prof. Dr. Colin Stark from the Earth Observatory, Prof. Dr. Gabriel Wolken from the University of Fairbanks, Alaska, and Dr. Anja Dufresne, LIH (at the time a visiting researcher at FLNRO) flew to Haines, Alaska from where they chartered a small plane to cover the last kilometers to the landslide on Lamplugh Glacier. They spent two days gathering field evidence and performing an airborne photogrammetry survey. The results of their study are now published in the journal Landslides (Dufresne et al., 2019).

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Slope instability and tsunami hazards at Grewingk Glacier and Lake

hill with parallel cracks Copyright: Ground Truth Trekking under the Creative Commons Attribution Non-Commercial license Figure 3. Slope parallel cracks, steep rock slopes, a retreating glacier with a deepening lake at its toe, and a past slope collapse that sent a 60 m tsunami across Grewingk Valley in 1967 make this site an urgent place for studying slope stability.

The current accelerated climate warming and retreating glaciers are linked to an increase in slope failure activity, from heightened rockfall to the collapse of entire slopes. In some areas of Alaska, large rock slope failures do not only occur more often, but also seem to increase in size per event. Grewingk Glacier and Lake in Kachemak Bay State Park on the Kenai Peninsula (south of Anchorage, Alaska) exhibits many risk factors: rapid glacier retreat, documented history of a deep-seated tsunamigenic failure, high and steep slopes, frequent minor failures, signs of active cracking in the ridge, and deep water. It is also a popular tourist destination, attracting as many as 100 people on a busy summer day.

With a first grant (DU1294/4-1) supporting the initiation of international collaborations from the German Research Foundation (DFG), Anja Dufresne and Pooya Hamdi from LIH visited Grewingk Lake and Glacier across the Bay from Homer, Alaska. During our site visit, we hiked to the scarp of the 1967 landslide, which produced a tsunami in the proglacial lake and delta. The survey was organized by Bretwood Higman from Ground Truth Trekking, and in cooperation with Edward Berg from the University of Alaska, Kenai Peninsula College.

   

Publications:

  • Higman B, Geertsema M, Shugar D, Lynett P, Dufresne A (2019). The 2015 Taan Fiord landslide and tsunami. Alaska Park Science, Understanding and Preparing for Alaska’s Geohazards 18(1): 7-16.
  • Dufresne A, Wolken G, Hibert C, Bessette-Kirton E, Coe J, Geertsema M, Ekström G (2019). The 2016 Lamplugh rock avalanche, Alaska: Deposit structures and emplacement dynamics. Landslides, https://doi.org/10.1007/s10346-019-01225-4
  • Higman B, Shugar D, Stark CP, Ekström G, Koppes M, Lynett P, Dufresne A, Haeussler P, Geertsema M, Gulick S, Mattox A, Venditti JG, Walton MAL, McCall N, McKittrick E, MacInnes B, Bilderback EL, Tang H, Willis MJ, Richmond B, Reece B, Larsen C, Olson B, Capra J, Ayca A, Bloom C, Williams H, Bonno D, Weiss R, Keen A, Skanavis V, Loso M (2018). The 2015 landslide and tsunami in Taan Fiord, Alaska. Nature Scientific Reports 8(12993).
  • Dufresne A, Geertsema M, Shugar D, Koppes M, Higman B, Haeussler P, Stark C, Venditti J, Bonno D, Larsen C, Gulick SPS, McCall N, Walton MA, Loso MG (2018). Sedimentology and geomorphology of a large tsunamigenic landslide, Taan Fiord, Alaska. Sedimentary Geology – Special Issue ‘Evidence of Geohazards’: 364, 302-318.

Conference presentations:

  • Higman B, Dufresne A, Berg E, Geertsema M, Lynett P, Roberts N, Loso M (2019). Lessons from Taan Fiord and Lituya Bay: is Alaska’s Grewingk Lake poised for catastrophe? AGU Fall Meeting 9-13 December 2019, San Francisco, CA, USA.
  • Koppes MN, Williams H, Geertsema M, Dufresne A (2019). Hazards of a changing cryosphere: a comparison of glacial and paraglacial responses to rapid glacial retreat in coastal fjords. AGU Fall Meeting 9-13 December 2019, San Francisco, CA, USA.
  • Dufresne A, Geertsema M, Shugar DH, Koppes M, Higman B, Haeussler PJ, Stark C, Venditti JG, Bonno D, Larsen C, Gulick SPS, McCall N, Walton M, Loso MG, Willis MJ (2018). The October 2015 tsunamigenic landslide in Taan Fiord, Alaska. EGU General Assembly, Vienna, Austria, 8-13 April 2018.
  • Haeussler PJ, Stark C, Ekström G, Gulick S, Higman B, Bloom C, Bilderback E, Dufresne A, Geertsema M, Guiltier L, Jaffe B, Koppes M, Labay K, Larsen C, Loso M, Lynett P, McCall N, Richmond B, Reece B, Shugar D, Venditti J, Walton M, Weiss R, Williams H (2017). The seismologically detected Taan Fiord landslide and tsunami of 17 October 2015: preliminary findings. Seismological Society of America Annual Meeting, Denver, Colorado, USA, 18-24 April 2017.
  • Geertsema M, Wolken G, Stark C, Dufresne A (2016). Large ice-rock avalanches in Glacier Bay National Park. Centennial Science and Stewardship Symposium, Fairbanks, Alaska, 19-21 October 2016.