Volcano Update from Archive

Friday, February 13, 2009 10:12 AM AKST (Friday, February 13, 2009 1912 UTC)

Redoubt Volcano
60°29'7" N 152°44'38" W, Summit Elevation 10197 ft (3108 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

On the basis of current activity, the Alaska Volcano Observatory (AVO) continues to expect that the most likely outcome of current Redoubt activity is an eruption, similar or smaller in scale to the 1989-1990 eruption. It is not currently possible to determine exactly when such an eruption might occur. Based on observations of past eruptions of Redoubt, ongoing analysis of the current activity, and studies of similar volcanoes worldwide, the current period of elevated unrest could persist for some time, possibly many months. However, as long as substantial volcanic-gas emission, prolonged periods of tremor, and intermittent discrete, shallow earthquakes occur, notable escalation of activity immediately prior to an eruption might only be on the order of hours or less.

The alert level remains at ORANGE/Watch, and for the time being AVO is staffed 24/7. If seismicity or other monitoring data suggest that Redoubt may be rapidly escalating to an eruption, AVO will send out a notification.

Monitoring Summary

Unrest at Redoubt Volcano continues; no eruption has yet occurred.

Redoubt Volcano has been at elevated alert levels for the past three months. AVO raised the aviation color code to YELLOW and the alert level to ADVISORY on 5 November 2008 in response to elevated gas emissions and visual evidence of melting of ice near the volcano’s summit crater. AVO raised Redoubt’s aviation and alert levels to ORANGE/WATCH on 25 January 2009 in response to a sharp increase in seismicity detected beneath the volcano. Since 25 January 2009, AVO also has detected corresponding increases both in the rate of glacial melting and of magmatic gas emissions at the volcano’s summit.

The Observatory facility in Anchorage currently is staffed 24 hours a day. AVO staff continues to conduct visual surveillance of the volcano via the web cam and overflights, airborne measurements of gas output, seismic analysis, and examination of satellite and weather-radar data.

In response to this elevated unrest, AVO has: conducted ten overflights of the volcano to make visual observations and gas measurements; installed a web camera, two more seismic stations, and a GPS sensor close to the volcano; redirected a webcam on a platform in the Cook Inlet to view Redoubt; assisted in the installation of lightning-detection equipment on the Kenai Peninsula, and improved the telemetry system that transmits data to the Observatory. Additional upgrades of the Redoubt monitoring system, water sampling, and overflights for observation and gas measurements are planned over the next several weeks as weather permits.

Analysis of Current Unrest

Analysis of monitoring data suggests that the current episode of unrest results from the intrusion of new magma beneath the volcano. The main evidence for the presence of this magma is: (1) measurement of substantial amounts of magmatic gas (thousands of tons per day of carbon dioxide) being emitted from the volcano’s summit area; (2) visual observations of high heat flux such as intermittent steam plumes, melting of the upper Drift Glacier (as much as 5-6 million cubic meters through February 10), and increased water discharge from the lower Drift Glacier, (3) elevated seismicity since 23 January 2009, including continuous shallow tremor that is consistent with the movement of fluids (including heated ground water) and gases within the volcano, and (4) deep earthquakes in December 2008 and January 2009 that may have marked magma movement.

We estimate that the new magma is beneath Redoubt at depths greater than about 5 km (about 3 miles), although a small amount of the magma may have risen to shallower depths in late January when seismicity, degassing, and melting intensified. There is no evidence to suggest that a large volume of magma is present at shallow depths (within 2 km, or about a mile, of the surface).

Comparison to Previous Periods of Volcanic Activity at Redoubt

There are few past examples of Redoubt eruptions that were well-monitored or well-observed. In 1965-1968, incomplete accounts indicate that elevated levels of unrest occurred for months before the onset of eruptive activity. In 1933, activity of Redoubt may have consisted only of a temporary increase in gas and heat output and no eruption.

The 1989-90 eruption is the only one that was seismically monitored, and seismic stations were emplaced mere months prior to the start of the eruption. Prior to the first explosive events in 1989, precursory seismicity ramped up quickly over a period of 23 hours. The eruption lasted from December 1989 until June 1990, and was characterized by explosive events that produced ash clouds reaching as high as 40,000 ft above sea level, separated by periods when lava domes grew in the summit crater. During the 1989-90 eruption, ash fall was greatest on the Kenai Peninsula, reaching a few (3-5) millimeters (0.1-0.2 inches) on one occasion, with trace amounts deposited in Anchorage and other communities in south-central Alaska. Ash clouds from the 1989-90 eruption also disrupted air traffic operations in and out of the Anchorage area and Kenai. Mudflows, formed as hot erupted material swiftly melted large volumes of snow and ice mantling the volcano, traveled down the Drift River and reached Cook Inlet, partially flooding the Drift River Oil Terminal facility.

Heavily ice-mantled Redoubt Volcano is located on the western side of Cook Inlet, 170 km (106 mi) southwest of Anchorage and 82 km (51 mi) west of Kenai, within Lake Clark National Park. Redoubt is a stratovolcano which rises to 10,197 feet above sea level. Recent eruptions occurred in 1902, 1966-68, and 1989-90.

More information about Redoubt Volcano can be found at http://www.avo.alaska.edu/activity/Redoubt.php

Tom Murray, Scientist-in-Charge, USGS

tlmurray@usgs.gov (907) 786-7497

Steve McNutt, Coordinating Scientist, UAF

steve@giseis.alaska.edu (907) 474-7131

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.