Report on Augustine (United States) — 7 December-13 December 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 7 December-13 December 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Augustine (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 7 December-13 December 2005. Smithsonian Institution and US Geological Survey.
59.363°N, 153.43°W; summit elev. 1252 m
All times are local (unless otherwise noted)
Seismicity remained at elevated levels at Augustine during 30 November to 12 December. On 12 December a steam plume visible on video and satellite images extended 75 km SE of the volcano. During 9-12 December, changes in the style of earthquake activity at the volcano were recorded and there were reports of gas emissions and steaming. Seismic events on 9 and 11 December may have perturbed the hydrothermal system, initiating steam explosions. These events were consistent with reports of steaming at the summit observed on 10 December, and a distinct sulfur smell ("like from a sewer") in the air on the evening of 11 December at Nanwalek and Port Graham, approximately 80 km E of the volcano. Augustine remained at Concern Color Code Yellow.
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.