Report on Augustine (United States) — 28 December-3 January 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 28 December-3 January 2006
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, 28 December-3 January 2006. Smithsonian Institution and US Geological Survey.
59.363°N, 153.43°W; summit elev. 1252 m
All times are local (unless otherwise noted)
Unrest continued at Augustine during 23-30 December. Seismicity rates decreased during the week, while steam-and-gas emissions continued. Brief views of the volcano during clear weather revealed that steam was continuously emitted from the volcano. The activity continued to suggest that new magma is present beneath Augustine. Based on past eruptions at Augustine, AVO expects to see a sharp increase in earthquake activity prior to a significant explosive eruption. 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.