Report on Augustine (United States) — 22 February-28 February 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 22 February-28 February 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, 22 February-28 February 2006. Smithsonian Institution and US Geological Survey.
59.363°N, 153.43°W; summit elev. 1252 m
All times are local (unless otherwise noted)
During 21-27 February, seismicity at Augustine was relatively low, but remained above background levels. Seismic data indicated that small rockfalls and avalanches from the lava dome occurred intermittently. A thermal anomaly was visible in the summit area on satellite and camera imagery. These data indicated that the lava dome at the volcano's summit continued to grow slowly. Observations during the report week revealed that a plume composed of variable amounts of gas, steam, and small amounts of ash was emitted intermittently from Augustine's summit. 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.