Report on Chiginagak (United States) — 24 August-30 August 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 24 August-30 August 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Chiginagak (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 24 August-30 August 2005. Smithsonian Institution and US Geological Survey.
57.135°N, 156.99°W; summit elev. 2221 m
All times are local (unless otherwise noted)
AVO reported that a 400-m-wide "melt-water lake" formed in the snow-and-ice filled summit crater of Chiginagak sometime after the previous observation in August 2004. Earlier this summer, the southern crater rim of Chiginagak was breached, allowing a portion of the lake to drain. The resulting lahar left a deposit on a glacier draining the crater to the S and caused flooding of 1-2 m above normal at Indecision Creek. The breach in the crater rim and the ensuing lahar probably occurred in July 2005; there were reports from a nearby lodge at this time of strong sulfur smells and cloudy, yellowish water in the Indecision Creek drainage. There were no indications that an eruption is imminent or that this event is necessarily precursory to an eruption. Chiginagak is not seismically monitored, so AVO did not assign it a Concern Color Code.
Geologic Background. The symmetrical, calc-alkaline Chiginagak stratovolcano located about 15 km NW of Chiginagak Bay contains a small summit crater, which is breached to the south, and one or more summit lava domes. Satellitic lava domes occur high on the NW and SE flanks of the glacier-mantled volcano. An unglaciated lava flow and an overlying pyroclastic-flow deposit extending east from the summit are the most recent products of Chiginagak. They most likely originated from a lava dome at 1687 m on the SE flank, 1 km from the summit of the volcano, which has variably been estimated to be from 2075 to 2221 m high. Brief ash eruptions were reported in July 1971 and August 1998. Fumarolic activity occurs at 1600 m elevation on the NE flank of the volcano, and two areas of hot-spring travertine deposition are located at the NW base of the volcano near Volcano Creek.