TSUNAMIGENIC LANDSLIDE HAZARDS IN COASTAL ALASKA: PAST AND PRESENT (Invited Presentation)

Coastal Alaska has been impacted by multiple large tsunamis generated by landslides. In 1958, an earthquake triggered landslide impacted Lituya Bay, producing a wave with runup > 500 meters in height adjacent to the landslide source and resulting in two fatalities. Prince William Sound experienced rapid uplift and substantial mass-wasting during the 1964 M9.2 earthquake. In the communities surrounding Prince William Sound, 85 of the 106 total fatalities were attributed to waves generated by submarine and subaerial landslides triggered during the earthquake. In 2015, a landslide generated a tsunami in Taan Fiord with runup height on the shore > 190 meters; fortunately, there were no fatalities during this event. While the causal mechanism is largely unknown, Taan Fiord has undergone rapid deglaciation in recent decades, and there was a small earthquake that preceded the event.

In June of 2019, a large slow-moving landslide was identified in Barry Arm, a recently deglaciated fjord in Prince William Sound, Alaska. The destabilized mass appears in historical photographs as early as 1937.The rapid retreat of the Barry Glacier terminus over the past two decades has increased the possibility of partial or catastrophic, en-masse failure of the slide mass into the fjord. This in turn, presents new potential to generate large displacement waves in Prince William Sound.

As a results of this hazard, local, state, and federal agencies are partnering to conduct scientific research to a) identify potentially tsunamigenic landslides in Prince William Sound, b) determine geologic and meteorologic controls on landslide movement, c) surveil potentially hazardous landslides to detect elevated rates of landslide motion that may presage failure, d) produce coupled landslide and displacement wave hazard and risk assessments in Prince William Sound, and e) provide input needed to develop early warning capabilities and increase situational awareness of potential hazards in the surrounding communities. This presentation will provide an overview of the historic events that have impacted coastal Alaska and describe ongoing efforts for advancing our understanding of landslide hazards for the purposes of reducing risk to communities, infrastructure, marine traffic, and recreationalists in Prince William Sound.