Report on Augustine (United States) — 11 January-17 January 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 11 January-17 January 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, 11 January-17 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)
Explosive activity began at Augustine on 11 January. The day before, AVO increased the Concern Color Code from Yellow to Orange when seismicity began to increase at the volcano. On 11 January at 0444 seismic signals began to be recorded that were interpreted as being associated with explosions at Augustine's summit. The Concern Color Code was increased to Red, the highest level. Another explosion occurred at 0513, and satellite imagery confirmed that an ash plume was produced that rose to ~9.1 km (30,000 ft) a.s.l. and drifted N and E. An ashfall advisory was issued by the National Weather Service. Seismicity decreased after the explosions. During a flight over the volcano, scientists saw volcanic mudflows on the E, S, and W sides of the volcano. Minor rock and snow avalanche deposits were visible high on the SW part of the edifice. According to news articles, several flights were canceled or diverted due to ash in air space.
On 12 January, the Concern Color Code was reduced to Orange. On 13 January, seismicity began to increase. An eruption on the 13th from about 0355 to 0439 produced an ash plume to 10.4 km (34,000 ft) a.s.l. On the 13th, the volcano entered a period of repetitive and explosive eruptions, with explosions occurring at 0444, 0847, 1122, and 1640. Each event produced ash plumes, mudflows, and pyroclastic flows. The ash plumes produced from these eruptions rose higher than 9.1 km (30,000 ft) a.s.l. Ash drifted ESE and a small amount of ash fell in communities of the SW Kenai Peninsula. Explosions on the 13th at 1858 and on the 14th at 0014 were similar in size and duration as the previous four. In response to these eruptions, the National Weather Service issued an ashfall advisory for the western Kenai Peninsula S of Ninilchik. No explosions were recorded later on the 14th. The level of seismic activity declined after an explosion on 14 January at 0016, so the Concern Color Code was reduced to Orange on 15 January at 0945. Observations on 16 January confirmed that pyroclastic deposits were widespread on the volcano's flanks, as seen in web camera images. Also, a small lava dome appeared to have extruded at the summit.
AVO reported on the 16th that the level of seismic activity at the volcano remained above background. It is likely, but not certain, that further explosive activity will occur. Explosive events similar to those of 13 and 14 January could occur with little or no warning.
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.