Mount Redoubt is an active stratovolcano located in Lake Clark National Park and Preserve 170 km (105 miles) southwest of Anchorage, Alaska's larges city. Redoubt is one of 40 active volcanoes in the Aleutian volcanic arc which stretches some 2,500 km (1,550 miles) across the north Pacific.
On December 13, 1989, following a dramatic increase in earthquake activity at Redoubt Volcano, the Alaska Volcano Observatory issued a warning of the increased likelihood of an eruption. The following day, an explosive eruption sent a column of ash and gas more than 10 km (6 miles) into the atmosphere. Over the next two days, additional explosive eruptions spread ash to the northeast, disrupting airline traffic as far away as south Texas and other activity throughout south central Alaska. By December 16, the eruption had steadied to a continuous, low-level ejection of ash and steam.
The explosions produced hot, fast-moving clouds of ash, rock debris, and gas that swept across Redoubt's heavily glaciated north flank. These events triggered massive debris flows in Drift River valley that threatened an oil tanker terminal near the river's mouth. Partial flooding of the terminal compound on two occasions forced authorities to modify its operating procedures, which temporarily halted oil production from 10 platforms in Cook Inlet. The damage and loss of revenue from ash and debris flows total about $160 million, making this eruption the second most costly in the history of the United States.
Scientist believe the ring (see left) is the snow and ice that vaporized with the initial blast but are not sure since this is the first time it has ever been observed at an eruption site.
On December 21, 1989, the continuous ash ceased and a large lava dome began forming in the summit crater. The explosive collapse of this lava dome on January 2, 1990 generated an eruption column accompanying pyroclastic flows and lahars. A similar cycle of dome emplacement and destruction was repeated twelve more times in the following months until the final lava dome emplaced on April 12, 1990.
If you would like more information on the Redoubt Volcano visit AVO's Redoubt Page.