Mount Redoubt, the volcano across Cook Inlet that erupted in the spring, is rumbling again.
The Alaska Volcano Observatory says a series of small earthquakes began Sunday afternoon near the summit and continued into Monday. As a result, scientists have upgraded the volcano's alert status.
The aviation code for Redoubt was elevated from green to yellow. That means the volcano is showing signs of unrest, though experts don't know if it will spew ash and lava again anytime soon. Flights aren't being affected. Nothing appears imminent.
"It is just as likely that this kind of activity will carry on for three days and then just die off," said Tina Neal, a geologist with the U.S. Geological Survey. "We don't want to make people unduly nervous."
Redoubt's lava dome has built up again to a massive size. Lava may be moving under the surface, or gas may be releasing, Neal said.
The 2009 eruption began in March and included what scientists call a number of individual events, with ash dusting Anchorage and beyond. Redoubt had reverted to code green, meaning in a typical, non-eruptive state, Sept. 29 and remained there until Monday's change in status.
After the shallow earthquakes began showing up Sunday, scientists started a night watch that will continue until the volcano calms down, geophysicist Dave Schneider said.
While the observatory isn't being staffed 24-7 at this point, scientists monitor the volcano from home and get alerts on cell phones, he said. Scientists plan to fly to the volcano to collect samples and get a better look when the weather allows.
The eruption prompted Cook Inlet Pipe Line Co. to remove several million of gallons of oil stored at the Drift River Terminal 22 miles away. The terminal collects production from many Cook Inlet oil platforms and loads the oil onto tankers.
Hundreds of airline flights were diverted from Anchorage this spring over concerns that ash clouds could damage jet engines.
The last time Redoubt had a similar period of activity was in 1989 and 1990.
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