Report on Augustine (United States) — 12 April-18 April 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 12 April-18 April 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Augustine (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 12 April-18 April 2006. Smithsonian Institution and US Geological Survey.
59.363°N, 153.43°W; summit elev. 1252 m
All times are local (unless otherwise noted)
Activity at Augustine declined to low levels during 7-14 April, with seismicity decreasing to slightly above background levels, and rockfalls and avalanches decreasing in frequency in comparison to previous weeks. Low-level eruptive activity continued, consisting of slow effusion of lava at the summit accompanied by small rockfalls and avalanches on the volcano's flanks. Satellite imagery showed a decline in thermal output consistent with the decreased activity. Sulfur-dioxide gas measurements showed continued high levels of magmatic gas emissions that may have been associated with degassing of lava at the summit of the volcano. Augustine remained at Concern Color Code Orange.
Geologic Background. Augustine volcano, rising above Kamishak Bay in the southern Cook Inlet about 290 km SW of Anchorage, is the most active volcano of the eastern Aleutian arc. It consists of a complex of overlapping summit lava domes surrounded by an apron of volcaniclastic debris that descends to the sea on all sides. Few lava flows are exposed; the flanks consist mainly of debris-avalanche and pyroclastic-flow deposits formed by repeated collapse and regrowth of the volcano's summit. The latest episode of edifice collapse occurred during Augustine's largest historical eruption in 1883; subsequent dome growth has restored the volcano to a height comparable to that prior to 1883. The oldest dated volcanic rocks on Augustine are more than 40,000 years old. At least 11 large debris avalanches have reached the sea during the past 1800-2000 years, and five major pumiceous tephras have been erupted during this interval. Historical eruptions have typically consisted of explosive activity with emplacement of pumiceous pyroclastic-flow deposits followed by lava dome extrusion with associated block-and-ash flows.