Report on Iliamna (United States) — 9 January-15 January 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 January-15 January 2013
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2013. Report on Iliamna (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 9 January-15 January 2013. Smithsonian Institution and US Geological Survey.
60.032°N, 153.09°W; summit elev. 3053 m
All times are local (unless otherwise noted)
On 9 January, AVO reported that unrest at Iliamna had decreased over the past several months, reaching background levels. The Volcano Alert Level was lowered to Normal and the Aviation Color Code was lowered to Green. The report also noted that occasional small earthquakes had continued, but at a greatly reduced rate and magnitude relative to the peak of unrest in March 2012. Steam and sulfur gas emissions continued to be observed from sites near the summit during periods of favorable meteorological conditions, not unusual at Iliamna.
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.