AVO reported that during 15-21 April seismicity from Redoubt remained above background levels, indicating ongoing growth of the lava dome in the summit crater. The web camera showed that vigorous steam-and-gas plumes that may have occasionally contained small amounts of ash rose from the vent to altitudes below 4.6 km (15,000 ft) a.s.l. Analysis of satellite imagery revealed thermal anomalies at the summit and drifting sulfur dioxide plumes. Based on photos and thermal images obtained on 16 April, the lava dome was estimated to be about 500 x 700 m across and at least 50 m thick. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Geological Summary. 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.

Source: US Geological Survey Alaska Volcano Observatory (AVO)