The most recent (AD 1883) debris avalanche formed a 10-m (33 ft) tsunami at low tide in a coastal community 85 km (53 mi) eastward. A much larger and swifter debris avalanche plowing into the sea at high tide could produce a tsunami far more hazardous to the growing population of Cook Inlet. Some of the hummocks of a great avalanche forming West Island 300-400 yr ago were planed off as the West Island avalanche smashed into the sea perhaps at high tide. A discontinuous coarse sand layer on West Island and locally on adjacent on the mainland on the east side of Cook Inlet suggests a consequent tsunami.
Domebuilding during five historical eruptions between 1883 and 1986 has restored a summit cone to a volume and steepness like that just before the 1883 debris avalanche. With unstable slopes and a pattern of increasing frequency of eruptions since 1812, might Augustine deliver a catastrophe to southern Cook Inlet a within a decade or so?
Waitt, R.B., and Beget, J.E., 1991, Debris avalanches from summit domes of Augustine Volcano sometimes cause tsunamis in Cook Inlet, Alaska: Eos, Transactions American Geophysical Union, v. 72, p. 227-228.
Waitt, R.B., and Beget, J.E., 1996, Provisional geologic map of Augustine volcano, Alaska: U.S. Geological Survey Open-File Report 96-516, 42 p., and map at scale 1:25,000.
