Information Statement of Friday, February 13, 10:12 AM AKST
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.