Report on Augustine (United States) — 15 March-21 March 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 15 March-21 March 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, 15 March-21 March 2006. Smithsonian Institution and US Geological Survey.
59.363°N, 153.43°W; summit elev. 1252 m
All times are local (unless otherwise noted)
Low-level eruptive activity continued at Augustine during 10-17 March. The seismicity changed from periods of prolonged volcanic tremor and closely spaced discreet earthquakes to episodic short-duration events. This change indicated that steady effusion of lava and dome growth gave way to activity characterized by slower effusion of lava and intermittent block-and-ash-flows, rock avalanches, and rockfalls originating from the summit lava dome. Observers saw numerous hot avalanches and prolonged periods of incandescence in the summit area and on the upper NE flank on several evenings. Satellite images showed that thermal anomalies persisted. Observations made during overflights of the volcano indicated that two lava flows on the N and NE flanks continued to advance slowly. Occasional collapses of the lava-flow fronts shed hot blocks and produced minor ash emissions. Photographs indicated that the new lava dome was about 70 m higher than the level of the lava dome formed in 1986. 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.