On Sunday, January 25, 2009, we were abruptly shaken by a fairly strong earth quake reported to have been in the 6.2 magnitude range in the Kenai Area. This was followed by the warnings from the Alaska Volcano Observatory that the possibility of an eruption of Mount Redoubt Volcano is quite possible in the next few days.
The last time Mount Redoubt erupted was back in December of 1989 and it was quite a show. We had just moved to Kenai at the time from Anchorage and remember this event very well. There was a fair amount of ash everywhere on the west side of the Kenai Peninsula and on up into the Anchorage area.
Today, January 28, 2009, the folks at the Alaska Volcano Observatory are still cautioning everyone that the possibility of an eruption is likely and to keep your disaster preparedness kits close by at all times.
Here is an interesting prospective from the folks at the Alaska Volcano Observatory. I recieved this in my email this morning. 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
Summary of Current Unrest Since last fall, the Alaska Volcano Observatory (AVO) has detected increasing volcanic unrest at Redoubt Volcano. Starting on Friday, January 23, the level of seismic activity increased markedly, and on Sunday AVO raised the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH. On the basis of all available monitoring data AVO regards that an eruption similar to or smaller than the one that occurred in 1989-90 is the most probable outcome. We expect such an eruption to occur within days to weeks. In response to the current increase in activity, AVO has deployed a web camera approximately 7.5 miles north-northwest of the summit and will install additional seismic equipment at the volcano as weather permits. A second web camera also is pointed at Redoubt from a platform within Cook Inlet. The observatory in Anchorage is currently staffed 24 hours a day. We plan continued visual surveillance of the volcano's summit region, frequent airborne measurements of gas output, and frequent analysis of satellite and weather-radar data. Observations and Background Beginning in September 2008, AVO received reports of a strong hydrogen sulfide (H2S) odor downwind of Redoubt. During an observation flight on September 26, a melt hole was observed in the upper Drift glacier, down slope from the location of historical eruptive vents. Gas-measurements flights in October and November detected elevated levels of sulfur dioxide (SO2), carbon dioxide (CO2), and H2S. Through the fall, melt holes increased in size, and several points of steaming and gas emissions were observed in the area of the lava domes extruded during the 1989-90 and 1966-68 eruptions. Concurrent with visual observations and gas data, a subtle increase in seismic activity was also detected beneath the volcano. Seismicity took the form of episodic, very weak volcanic tremor, consistent with the movement of fluids and gases within the volcano. AVO also located deep (30 km, or 19 miles, below sea level) long-period earthquakes, which were few in number but possibly indicative of magma recharge deep within Redoubt's plumbing system. Beginning on the evening of Friday, January 23, 2009, seismic activity increased at stations closest to Redoubt's summit. The seismicity consists of a combination of discrete, relatively small earthquakes and periods of more continuous volcanic tremor. This activity intensified early Sunday morning, January 25, at which time AVO raised the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH. Since Sunday, seismicity has waxed and waned but has remained well above background levels. The seismic unrest observed over the past few days is unusual for Redoubt and has not been seen since just prior to the 1989-90 eruption. Overflights on January 26 and 27 documented continued production of water vapor and volcanic gas plumes from the summit crater; increased melting has produced small flows of debris at the north base of the volcano. The most recent eruptions of Redoubt, in 1966-68 and 1989-90, were characterized by large explosions that produced ash clouds reaching as high as 40,000 ft asl. During the 1989-90 eruption, the largest ash fall from a single event in Kenai was 5 millimeters (0.2 inches), but ash fall was widespread and noted as far away as Fairbanks, along the Richardson Highway, and the Yukon Territory border. Other ash-producing events during the 1989-90 eruption deposited several millimeters of ash on the Kenai Peninsula and trace amounts of ash in Anchorage and more distant locations over several months. The 1989-90 eruption also several disrupted air traffic operations in and out of Anchorage. Other hazards from past and likely future eruptions include hot pyroclastic flows that may travel several miles from the volcano, especially to the north, and volcanic mudflows, or lahars, that travel many miles from their source. Lahars form as hot pyroclastic flows, often caused by collapse of a growing lava dome, swiftly melt large volumes of snow and ice downslope of the summit crater. In 1989-90, lahars flowed east down the Drift River, at least three of which reached Cook Inlet and one of which partially flooded the Drift River Oil Terminal facility. Lahars produced by eruptions of Redoubt Volcano may range from dense, gravel-rich flows to watery, sediment-laden floods. All such flows can transport boulder-size particles, and water within these flows temporarily may be at boiling temperatures. It could take a typical lahar 1-2 hours to travel from the base of the volcano to the mouth of the Drift River. Interpretation and Hazards Based on our current understanding of Redoubt's past eruptions, both historical and from the geologic record, and our analysis of the current episode of unrest, AVO considers the following future scenarios as possible:
- Failed Eruption: No eruption occurs because magma does not reach the
surface. Earthquake activity, gas output, and steaming slowly decrease over
several weeks or months. Continued heat flux may cause continued, modest
melting of snow and ice on the edifice and subsequent increased, but not
hazardous outflow into the Drift River.
- Eruption similar to or smaller than 1989-90: Unrest continues to escalate
culminating in an eruption that is similar to or smaller than the one that
occurred in 1989-90. An eruption such as this would likely spread volcanic
ash throughout Cook Inlet and other parts of south-central Alaska depending
upon the prevailing winds. Communities around the volcano, especially to the
east, northeast, and southeast, would likely experience trace to several millimeters
(less than 0.4 inches) of ash fall as a result of discrete explosive events.
Such events could also generate pyroclastic flows that swiftly melt snow and
ice to form mudflows, or lahars, that would likely travel east down Drift River,
possibly reaching and flowing into Cook Inlet. If summit lava domes form, as
they did in 1989-90, they may repeatedly collapse and generate pyroclastic
flows that would likely travel north from the summit crater and form lahars.
Smaller lahars could also form in other drainages if hot debris accumulated
on other flanks of the volcano. An eruption consisting of multiple explosive
events, episodic lava-dome growth and collapse, and lahars may last weeks to
months.
- Larger Explosive Eruption: A significantly larger eruption could occur, perhaps
similar to eruptions that are thought to have taken place prehistorically.
Such an eruption might involve the production of larger ash clouds, pyroclastic
flows on several flanks of the volcano, and larger lahars more frequently reaching
Cook Inlet down Drift River and affecting other drainages around the volcano
as well.
- Flank Collapse: The intruding magma or other processes could destabilize
a portion of the Redoubt edifice that could result in a large volcanic landslide.
At least twice in the last 10,000 years, debris flows generated by such landslides
have reached Cook Inlet. It is also likely that a landslide of this type would
be accompanied by an eruption. Because of the scarcity of these events in the
geologic record, a flank collapse and eruption is considered very unlikely.
A flank collapse may be accompanied by visible deformation of the edifice and
AVO will be looking for such signs.
Based on all available monitoring data and AVOs knowledge of the volcano, scenario number two, an eruption similar to or smaller than that of 1989-90, appears to be the most probable outcome at this time. We consider one and three to be somewhat less likely, and scenario four to be much less likely.
Comparing the time frame of pre-eruptive activity in 1989-90 (the only other eruption for which seismic data were available) with the current unrest, we would expect such an eruption to begin within the next few days or weeks. It is likely that the onset of an explosive eruption would be preceded by a further increase in seismicity. An explosive eruption would be accompanied by a sharp increase in seismicity. Should earthquake activity or other monitoring data suggest that an eruption is expected within hours, or is underway, AVO would move Redoubt from its current Aviation Color Code ORANGE to RED, and Alert Level WATCH to WARNING.
More information about Redoubt Volcano can be found at http://www.avo.alaska.edu/activity/Redoubt.php
