Scientists are continuing to take the pulse of Redoubt Volcano in Lake Clark National Park and Preserve 24 hours a day. While more than a week ago they were saying an eruption was "imminent," this week they've stepped away from that pronouncement somewhat.
Here's the latest from the Alaska Volcano Observatory:
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:
1. 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.
2. 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.
Hazards associated with this type of eruption:
* Ash clouds - Ash could reach 40,000 ft ASL or higher
* Ash fall - depending on prevailing winds, trace (< 1 mm) to minor amounts of ash (several millimeters) may fall in areas throughout Cook Inlet and southcentral Alaska. A trace of ash could also fall in other areas of southern and eastern Alaska.
* Lahars (mudflows) - lahars could travel east down the Drift River or within other drainages emanating from the volcano, possibly reaching the Cook Inlet.
* Pyroclastic flows - Fast-moving clouds of hot ash and gas could travel swiftly down the flanks, affecting areas mostly within about 15 km of the volcano.
Duration - Hazards from ash in the atmosphere, ash fall, lahars, and pyroclastic flows could persist for weeks to months.
3. 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.
4. 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.
Science can at times be inexact. It's not always cut and dried. That's what makes it so fascinating.
For the latest on Redoubt, check out AVO's website. There you'll find maps depicting ash trajectory predictions, latest photos, seismic readings, and other data.