Avalanche and landslide seismicity

Headwall of the 2004 ice avalanche on Mt. Steller, Alaska.

Landslides and avalanches produce a characteristic seismic signal that is easily distinguished from the groundshaking produced by earthquakes. The avalanches that I study are unusual in that they also exhibit a sequence of earthquakes prior to failure: in other words, they give warning before the avalanche occurs. These events are common on Iliamna volcano, Alaska, but have also been recorded on Mt. Baker, WA and on Mt. Steller, in the Chugach mountains of Alaska.

The major question that I hope to answer in studying these events is why some avalanches exhibit precursory seismicity while others do not. Thus far my research suggests that this seismic signal is unique to ice avalanches that exhibit "slab failure". In such events slip initiates at the base of a layer of ice, or within the layer of rock immediately beneath the ice. The headwalls of these avalanches clearly show that ice has been removed to the ice-rock interface (see figures).

Although these signals are not unique to volcanoes, it is likely that geothermal energy from the volcanic edifice promotes avalanche failure. Consequently, volcanoes are an excellent place to study them. Furthermore, avalanches on Iliamna and Mt. Baker appear to recur at several-year intervals, initiating from the same part of the mountain.

Headwall of the 1994 ice avlanche onĀ Iliamna volcano, Alaska. Note that the avalanche removed material to the ice-rock interface. Fumaroles near the summit suggest that internal heating may promote slip at the glacier base.