MELTWATER ORIGIN FOR THE 2005 MOUNT STELLER, ALASKA LANDSLIDE

On September 14, 2005, a massive landslide originated from just below the south-facing summit of 3,236-m-high Mount Steller, Alaska, removing a near-summit hanging glacier and a substantial amount of rock and snow. Much of the displaced slide mass landed on the surface of an unnamed tributary of Bering Glacier, nearly 2,500 m below. The slide runout extended more than 8 km down the glacier from the point of impact. Much of the summit area surface from which the slide occurred had a slope >50^o. The volume of the slide was estimated by the Alaska Volcano Observatory to be approximately 50x 10⁶ m³. Unlike most large Alaskan glacier-related landslides, this one was not triggered by an earthquake. However, the energy that the slide released was intense enough to generate a seismic signal recorded around the world with magnitudes of 3.8 to greater than 5.

Several just publicly released, one-meter resolution electro-optical images collected by U.S. National Systems in October 2005, provide new evidence pertaining to processes active at the summit at the time of the slide. Previously, Huggel and others (2008) proposed a warming of bedrock permafrost temperatures with possible destabilization processes resulting from water infiltration and refreezing, effective through a system of cracks and hydrostatic pressure variations in cracks and micro-fractures, as the cause of the slide. Molnia and others (2006) described glaciological evidence that suggested that a large volume of water had recently flowed on Mt Steller's east ridge and that englacial meltwater had a role in triggering the landslide.

The newly released National Systems imagery shows evidence of liquid water flowing out of a moulin or englacial stream channel from the truncated glacier ice face on the east wall of the landslide scarp and fractured ice that corresponds to another part of the englacial channel on the west flank of the scarp. The presence of these unusual glacial-hydrologic features at an elevation above 3,000 m, suggests an unusually large melting of summit snow and ice, a process confirmed by sequential imagery. This is supported by the newly released imagery. The presence of a large volume of meltwater close to Mt. Steller’s summit raises questions about regional climate change and its role in the future generation of landslides at higher elevations and latitudes.