Eruption of Mount Redoubt, Alaska 2009

Volcano Occurs Within 24 Hours of Issuing Orange Alert

Mar 23, 2009

Mount Redoubt, located on the shores of Cook Inlet in Alaska, had been dormant for 20 years. The last eruption occurred on December 14, 1989 and lasted for six months.

The Alaska Volcano Observatory (AVO) reported that Mount Redoubt began to erupt on March 22, 2009 at 10:38 pm with an estimated plume height of 20,000 feet above sea level. Within 20 minutes, the plume height soared to 50,000 feet.

Events Leading to the Eruption of Mount Redoubt

Mount Redoubt started to show signs of unrest on January 23rd, 2009. Monitoring data indicated that an eruption similar to the one in 1989 to 1990 would most likely occur again.

Web cameras were set up in several places around the mountain to observe activity. The observatory in Anchorage began to continually measure atmosphere conditions and review satellite data.

On Sunday, January 25th, 2009, the AVO raised the Aviation Color Code to Orange and the Volcano Alert Level to Watch. These codes mean that the volcano was exhibiting heightened or escalating unrest with increased potential of eruption, though the timeframe was uncertain.

Monitoring of Mount Redoubt continued throughout February. Additional web cameras were installed along with more seismic stations and a sensor close to the volcano. Approximately every three days, planes flew over the mountain to observe activity and to measure gas emission.

It was determined that the seismic activity on Mount Redoubt was due to the influx of new magma beneath the volcano. The emission of steam plumes was melting the ice on upper Drift Glacier. The shallow tremors on the mountain were attributed to the movement of ground water, other liquids and gases. On the summit of the mountain, large amounts of magmatic gas were escaping.

From February 26, to March 15, 2009, the level of activity subsided on Mount Redoubt. The Aviation Color Code was reduced to Yellow and the Volcano Alert Level was reduced to Advisory. Monitoring continued but not 24 hours a day.

On March 15, 2009, volcanic activity resumed and the warning levels were increased to Orange and Warning. Tremors became more frequent and high gas emissions were measured. A plume of ash and steam was also observed. Activity decreased again and the warnings were lowered to Yellow and Advisory

On March 21. 2009, activity increased again. Earthquake activity intensified and a small steam plume was observed at the summit. Round the clock observation resumed. At 10:00pm, the warning levels were put back up to Orange and Watch. Shallow earthquakes were increasing and at times, they were only a few minutes apart.

Eruption of Mount Redoubt

At 10:38pm on March 22, the alerts were changed to Red and Warning. When the first eruption occurred. This means a hazardous eruption was in progress along with the emission of volcanic ash into the atmosphere.

As of March 23, at 1:45am, it was reported that two additional large explosions had occurred. The next explosion was at 11:02pm followed by another on March 23, 2009 at 12:14am.