Description: From McGimsey and others (2007): "On May 15, 2005, AVO seismologists noted a swarm of unusual seismic activity at Iliamna. The events were emergent and prolonged (longest lasted 5-8 minutes), and were strongest at seismic station ILS, located on the south flank of South Twin (see fig. 14 in original text). The activity began about 1250 UTC and tapered off at 1718 UTC. Analysis revealed that the signals most likely were caused by a surficial process, such as a snow avalanche - a common occurrence on Iliamna - but this particular event lacked the usual precursory seismicity preceding other Iliamna snow and ice avalanches (J. Caplan-Auerbach and others, 2004; J. Caplan-Auerbach, written commun., 2005; Caplan-Auerbach and Huggel, 2007.) Corroborating evidence arrived on the morning of May 17 when Lee Fink of Lake Clark National Park called AVO to offer his observations from an overflight of the area the previous day. Fink reported seeing a large, fresh rock slide (not a snow or ice avalanche) southeast of Iliamna that began about the 6,500-ft level on the southeast flank of South Twin and ran down to about the 1,200-ft elevation (see fig. 15 in original text). The lengthy ridge extending south of Iliamna that includes South and North Twins and a large unnamed massif has steep, exposed sections of bedrock that frequently generate rock falls, and occasionally large rockslides, such as occurred on May 15 at South Twin."