Report on Augustine (United States) — 26 April-2 May 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 April-2 May 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, 26 April-2 May 2006. Smithsonian Institution and US Geological Survey.
59.363°N, 153.43°W; summit elev. 1252 m
All times are local (unless otherwise noted)
AVO reduced the Concern Color Code at Augustine from Orange to Yellow on 28 April. As of the 28th, instrumental and visual observations indicated that the growth of the summit lava dome and lava-flow emissions had stopped, or continued at very low rates. Seismic data showed that rockfalls and avalanches occurred at a diminished level. No changes were seen at the summit during the previous several weeks. AVO warned that despite the apparent cessation of lava-dome growth, the new dome and lava flows are still highly unstable, and rockfalls and avalanches are still occurring and may continue for several weeks or months.
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.