This hilly terrain is the surface of the debris avalanche deposit from summit collapse about 250-450 years ago, which forms the entire 2 x 3 km wide West Island. There are more than 1,000 hummocks of heights up to 30 m across the island. Bathymetric surveys suggest that the avalanche traveled an additional 3 km beyond the margin of West Island. Kamishak Bay and the Chigmit Mountains are on the horizon to the NW.

Photo by Lee Siebert, 1986 (Smithsonian Institution).

Keywords: hummocky | deposit | debris avalanche | debris avalanche deposit

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