Report on Iliamna (United States) — September 1996
Bulletin of the Global Volcanism Network, vol. 21, no. 9 (September 1996)
Managing Editor: Richard Wunderman.
Iliamna (United States) Increased seismic activity persists in September and early October
Please cite this report as:
Global Volcanism Program, 1996. Report on Iliamna (United States) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 21:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199609-313020.
60.032°N, 153.09°W; summit elev. 3053 m
All times are local (unless otherwise noted)
A small shallow earthquake swarm occurred beneath Iliamna during mid-May. After two months of ensuing quiescence, seismic activity increased on 1 August (BGVN 21:08). During September and the first half of October, 6 to 27 events were recorded each day at depths within the edifice to 9 km below sea level. Most of them were less than M 1.0 and the largest was M 3.2. All events seemed to be volcano-tectonic, and no long-period earthquakes or tremors that usually precede eruptions were detected. This seismicity was likely related to an intrusion of magma, but doest not mean that an eruption is imminent.
Geologic Background. 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; NOAA/NESDIS Satellite Analysis Branch (SAB), Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA.