Report on Redoubt (United States) — 25 March-31 March 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 March-31 March 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, 25 March-31 March 2009. Smithsonian Institution and US Geological Survey.
60.485°N, 152.742°W; summit elev. 3108 m
All times are local (unless otherwise noted)
On 25 March, AVO reported that a small explosion from Redoubt produced an ash plume that rose to an altitude of 4.6 km (15,000 ft) a.s.l. and drifted N to NW. Later that day AVO lowered the Volcanic Alert Level to Watch and the Aviation Color Code to Orange because seismicity had decreased during the previous 36 hours. On 26 March, multiple explosive eruptions produced plumes to altitudes of 6.1-19.8 km (20,000-65,000 ft) a.s.l. or greater. AVO raised the Alert Level to Warning and the Aviation Color Code to Red, the highest levels. The largest eruption, at 0924, also produced a lahar in the Drift River valley that was detected by seismic instruments.
During 27-28 March, seven explosive eruptions produced ash plumes to altitudes of 7.6-15.2 km (25,000-50,000 ft) a.s.l. An ash plume on 29 March rose to an altitude of 6.1 km (20,000 ft) a.s.l. Seismic and infrasound data did not show clear evidence that the plume was generated by an explosion. On 30 March, continuously emitted ash plumes of varying intensities were observed in a web camera, on satellite and radar images, and by pilots, and rose to altitudes less than 6.1 km (20,000 ft) a.s.l. Occasionally, short-lived events produced ash plumes to an altitude of 8.2 km (27,000 ft) a.s.l. A thermal anomaly at the vent seen on satellite imagery was possibly due to the extrusion of a lava dome in the summit crater. On 31 March, emissions of steam, gas, and minor amounts of ash were seen on Redoubt Hut web camera. Resultant plumes rose to altitudes of 4.6-7.6 km (15,000-25,000 ft) a.s.l. Satellite images showed a broad layer of volcanic haze that extended E over the Kenai Peninsula, the Anchorage Bowl, and the Matanuska-Susitna Valley.
According to news articles, 11 people were evacuated on 23 March from the Drift River Terminal, an oil storage facility about 35 km ENE of Redoubt that shut down because of the eruption. During 24-28 March, flights in and out of Anchorage and other local areas continued to be canceled or diverted; as many as 185 Alaska Airlines flights had been canceled since the beginning of the eruption. Ashfall was occasionally reported in Anchorage and areas NW.
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.