At 0800 on 19 March Reeve Aleutian Airways pilots Edward Livingston and Dale Schram observed a large steam plume rising about 1100 m above the summit. No ash appeared in the plume. Almost 3 hours later Northern Air Cargo pilot Wallace Niles observed a steam plume rising 1,000 m above the summit from a upper S flank vent. The plume drifted NNW. John Reeder noted that minor steam emissions are nearly continuous from Iliamna but a large steam plume is unusual.

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: J. Reeder, ADGGS.