Lessons from Taan Fiord and Lituya Bay: is Alaska's Grewingk Lake poised for catastrophe?

Grewingk Lake - a deep proglacial lake in Kachemak Bay State Park, Alaska - draws up to 300 visitors daily, some of whom camp within meters of the lakeshore. Before this popularity, a 80-Mm³ rock slide into the lake in 1967 and generated a tsunami that stripped forest from the surrounding landscape up to 60 m above lake level. Such a failure today could carry a high risk to park users, particularly during peak season, although its likelihood is unclear.

Glaciated landscapes like those found in Alaska are predisposed to large landslide-generated tsunamis during periods of glacial retreat. In particular, rapid glacial debuttressing exposes steep, unstable walls of ice-carved valleys hosting deep water in fjords or lakes. While landslides pose a direct hazard, this hazard can be broadcast over a larger area by tsunamis where deep water is present.

Such ingredients contributed to the 1967 Grewingk event, in which an actively deforming rock slope failed into 100 m of water, as well as to large landslide-generated tsunamis elsewhere in the glaciated landscapes of Alaska, Norway, British Columbia, Greenland, and Chile.

Prior to the 2015 Taan Fiord landslide-generated wave in Wrangell-St. Elias National Park, field observers and satellite measurements documented the unstable slope that ultimately produced the 65-Mm³ landslide and a consequent tsunami with peak runup of 193 m. Southeastern Alaska's Lituya Bay is famous for the extraordinary 1958 landslide-generated wave. However this was merely the most recent in a series of at least five such events in that bay. We hope our ongoing study of the Grewingk area will provide evidence to motivate mitigating action by the public and park officials. By better understanding this event and how it relates to other similar hazard cascades in Alaska, we aim to develop a framework for addressing the numerous sites that pose important yet thus far poorly understood hazards throughout the state, many frequented by tourists.