Report on Augustine (United States) — 21 December-27 December 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 21 December-27 December 2005
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, 21 December-27 December 2005. Smithsonian Institution and US Geological Survey.
59.363°N, 153.43°W; summit elev. 1252 m
All times are local (unless otherwise noted)
During 16-23 December, unrest continued at Augustine, with elevated seismicity and several small steam explosions occurring. Thermal imaging of the summit area on 22 December using a helicopter-mounted FLIR (Forward Looking Infrared Radiometer) confirmed the presence of a new, high-temperature fumarole or gas vent high on the S flank of the volcano. A gas-measurement flight on 20 December detected sulfur dioxide for the first time at Augustine since routine airborne measurements began in the early 1990s. Aerial observations and analysis of photography and video of the summit area indicated that some deformation occurred within the summit crater area. A crack or fissure was noted cutting the 1986 lava dome and extending to the SE. Heavy steam from this feature, along with patches of bare ground, indicated that heat output at the summit had increased. 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.