Report on Augustine (United States) — 1 February-7 February 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 1 February-7 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, 1 February-7 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 1-7 February, occasional pyroclastic flows continued to travel down Augustine's flanks and low-level ash plumes reached no higher than 4.6 km (15,000 ft) a.s.l. on satellite imagery. On 3 February, seismicity decreased significantly, but remained above background levels. Seismicity remained low throughout the remainder of the report period. Satellite imagery from the evening of 6 February showed a persistent thermal signal and occasional light ash emission. On 7 February, a steam plume was visible rising ~150 m (~500 ft) above the summit. AVO warned that further explosive activity producing ash clouds to heights over 7.6 km (25,000 ft) may still occur with little or no warning. 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.