Scientists at the Alaska Volcano Observatory have upgraded Mount Redoubt to alert level "advisory," aviation color code "yellow."
Starting around 4 p.m. on Sunday, staff at AVO observed small repetitive surface earthquakes coming from the 10,197-foot mountain, about 50 miles west of Kenai.
Tina Neal, a geologist with AVO, said the earthquakes have continued, becoming larger is size but less frequent.
She said this activity is similar to that seen in the spring when the volcano was erupting.
Neal said what this means remains unclear, but suggested three possibilities, including the eruption of lava, fluid moving toward the surface or the release of gas.
"The main point is the reappearance of activity has given us renewed concern about an eruption," she said.
Also of concern is the possibility of a collapse of the lava dome that formed in the volcano's crater during the last eruption.
In late August, AVO staff estimated the pile of hot and potentially explosive debris had reached over 88.6 million cubic yards.
That's enough material to fill a line of standard 15-yard dump trucks parked two across, bumper to bumper, stretching from Homer to Miami Fl., with some left overs.
If the dome collapses, Neal said it would be on par to an eruption, causing an ash cloud to move into the atmosphere while pyroclastic avalanches would spill down the Drift River Glacier Valley melting ice and snow, potentially causing flash flooding downstream.
As with all eruptive activity, Neal said there's also the possibility that this could fizzle out.
Neal noted that since the volcano quieted, Kenai Peninsula residents might have continued to see steam coming from the mountain on clear days. This is caused by heat emanating from the newly formed dome, she said.
"What we haven't had are shallow earthquakes, which indicates that something is happening that's a departure from the fall," she said.
Neal said an observation flight to measure gas emissions is being planned, as well as a check-up of monitoring equipment placed around the mountain.
"There's concern enough that were reminding people that it's unstable," she said.
After nearly two decades of quiet, AVO recorded elevated activity on Redoubt in mid-November of 2008. The volcano ultimately erupted on Mar. 22, and 19 explosive events followed over the next two weeks. The last eruption occurred on April 4.
In September the volcano was downgraded to color code green and alert level normal.
Dante Petri can be reached at email@example.com
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