Lenticular clouds forming over Redoubt on May 25, 2009. Image courtesy of AVO/USGS and sent to me by Eruptions reader Todd Russell.
We haven't talked much about Redoubt lately, so I thought I'd add a brief update. First off, the Alert Level at the volcano still sits at Orange/Watch status, meaning that although the volcano is not erupting, it could at almost any time.
Most of the threat of eruption stems from the ever-growing lava dome on the volcano. AVO noted today that the "Hut webcam views today show evidence of recent rockfall activity, including a fresh ash deposit to the east (left) of the lava dome and increased rock fall debris at the leading edge of the dome." This might suggest that small explosions are accompanying these rock falls, or that the rock falls are generating ash plumes associated with block-and-ash flows as the dome rock crumbles due to gravity and oversteepening. However, if the dome were to have a catastrophic collapse (which is likely but not guaranteed), then a larger explosive eruption might occur when the pressure is released on the underlying magma. And thus, the watch goes on.
The uncertainty surround Redoubt hasn't been all bad news for Alaska's economy. Some business that usually see little work during the summer months have been able to retool for summer work thanks to Redoubt.
Dr. Klemetti, Although I'm a biologist, I've been following the Rsam total seismisity monitor. I've noticed a general decrease over the last few weeks, is this situation normal for an erupting volcano of this type or might we be nearing an end of the current phase of extrusion?
I can reply to that answer: there haven't been explosive events anymore (there was a sudden burst of seismicity about a week ago though), but the lava dome growth process hasn't stopped and it doesn't seem to have slowed over the past 2-3 weeks. As their size increases, growing domes become more and more unstable and may collapse, triggering other(s) explosive events due to the sudden release of pressure. So in the case of Redoubt, the more time passes, the bigger the probability of this happening.
I do have a question for Dr.Klemetti too: the upper surface texture of the lava dome has become rather smooth compared to its early phases (less blocky). What does this mean? Has the lava composition changed over time?
There's a detailed information statement from AVO explaining the situation and the development of Redoubt status over the last few weeks here: http://www.avo.alaska.edu/activity/report_getter.php?need=current&id=41…
Erik, im guessing youve already seen this, but just incase.
Answering the question about the dome texture: my initial guess is that the dome material is likely not changing in composition. We saw in the 2004-08 eruptions at Mt. Saint Helens, the dome was extruded with a very smooth surface and that is believe to be related to conduit processes - almost as if the lava was being "polished" by the sides of the conduit as it was extruded. It could be the same thing going on here as more magma is erupted and the conduit becomes more well-defined ... however, that is just my guess at it right now.
Just a speculation, Erik: the 2004-8 dome at St Helens was an exceptionally quiet episode (for St Helens) with, apparently, a very low volatile content..could the smoother surface be related to a lower volatile content in the magma as the extrusion continues? (fewer explosive gas-releases breaking up the dome surface)
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