Report on Redoubt (United States) — 6 May-12 May 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 May-12 May 2009
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2009. Report on Redoubt (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 6 May-12 May 2009. Smithsonian Institution and US Geological Survey.
60.485°N, 152.742°W; summit elev. 3108 m
All times are local (unless otherwise noted)
AVO reported that during 6-12 May seismicity from Redoubt remained above background levels, indicating ongoing growth of the lava dome in the summit crater. Occasional rockfalls originating from the lava dome's flanks and steam-and-gas emissions were observed on the web camera. The emissions may have contained some ash. During 5-6 May, seismicity intensified and nearly continuous small earthquakes near the summit were recorded. Steam emissions were vigorous and minor ash was detected in emission by satellite imagery. Rockfalls also triggered ash emissions near the summit. On 6 May, tremor nearly doubled in intensity and the number of events increased. An ash emission produced a plume that rose to an altitude of 3.7 km (12,000 ft) a.s.l. Seismicity declined during 6-7 May but continuous small earthquakes continued to be recorded by stations near the summit. On 12 May, seismicity decreased to low levels compared to other phases of the eruption. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.
Geologic Background. Redoubt is a glacier-covered stratovolcano with a breached summit crater in Lake Clark National Park about 170 km SW of Anchorage. Next to Mount Spurr, Redoubt has been the most active Holocene volcano in the upper Cook Inlet. The volcano was constructed beginning about 890,000 years ago over Mesozoic granitic rocks of the Alaska-Aleutian Range batholith. Collapse of the summit 13,000-10,500 years ago produced a major debris avalanche that reached Cook Inlet. Holocene activity has included the emplacement of a large debris avalanche and clay-rich lahars that dammed Lake Crescent on the south side and reached Cook Inlet about 3,500 years ago. Eruptions during the past few centuries have affected only the Drift River drainage on the north. Historical eruptions have originated from a vent at the north end of the 1.8-km-wide breached summit crater. The 1989-90 eruption had severe economic impact on the Cook Inlet region and affected air traffic far beyond the volcano.