Report on Iliamna (United States) — October 1996
Bulletin of the Global Volcanism Network, vol. 21, no. 10 (October 1996)
Managing Editor: Richard Wunderman.
Iliamna (United States) Seismic swarm that began on 1 August continues through November
Please cite this report as:
Global Volcanism Program, 1996. Report on Iliamna (United States) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 21:10. Smithsonian Institution.
60.032°N, 153.09°W; summit elev. 3053 m
All times are local (unless otherwise noted)
The seismic swarm that began on 1 August beneath Iliamna (BGVN 21:08 and 21:09) continued during 12 October-29 November at an average rate of 3-12 earthquakes/day. The swarm center is ~5 km S of the summit. All events (mostly M <1.0) were <10 km deep and seemed to be volcano-tectonic. No long-period earthquakes or tremors that usually precede eruptions were detected. This seismicity was likely related to an intrusion of magma, but does not mean that an eruption is imminent.
Geological Summary. Iliamna is a prominentglacier-covered stratovolcano in Lake Clark National Park on the western side of Cook Inlet, about 225 km SW of Anchorage. Its flat-topped summit is flanked on the south, along a 5-km-long ridge, by the prominent North and South Twin Peaks, satellitic lava dome complexes. The Johnson Glacier dome complex lies on the NE flank. Steep headwalls on the S and E flanks expose an inaccessible cross-section of the volcano. Major glaciers radiate from the summit, and valleys below the summit contain debris-avalanche and lahar deposits. Only a few major Holocene explosive eruptions have occurred from the deeply dissected volcano, which lacks a distinct crater. Most of the reports of historical eruptions may represent plumes from vigorous fumaroles E and SE of the summit, which are often mistaken for eruption columns (Miller et al., 1998). Eruptions producing pyroclastic flows have been dated at as recent as about 300 and 140 years ago, and elevated seismicity accompanying dike emplacement beneath the volcano was recorded in 1996.
Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.