The Alaska Volcano Observatory raised the warning level for Okmok to yellow, or advisory, on Monday after a series of seismic bursts that lasted for six hours. The tremors repeated again Wednesday but have since subsided. AVO coordinating scientist Steve McNutt said these seismic signals could mean anything.
"Signals like this sometimes precede eruptions on the scale of hours to days, sometimes weeks or longer. And then sometimes the volcano just goes back to sleep," he said. "So you have to be cautious and assume that it may erupt and it could do so quickly, so that's the basis for our treating it with caution and changing the color code. On the other hand it could represent a new physical state of the volcano in which case it could do something different and then go back to sleep."
Okmok erupted very suddenly in July but that was unusual. Its current behavior is reminiscent of the tremors between 2003 and 2005. "It kind of turned on, turned off, turned on turned off. And we may be back to that activity now," McNutt said. But if Okmok erupts again, it is likely to be a small eruption.
Mount Cleveland is also marked yellow, but this is typical. It has small eruptions up to half a dozen times per year. McNutt explained that since there is no seismic network on the island to detect minor changes, it is safer to keep the Cleveland warning at yellow most of the time.
# posted by kevin : 9:25 PM
