Anchorage Daily News

After months of remaining on high alert, scientists at the Alaska Volcano Observatory say they are beginning to believe that Redoubt volcano's 2009 eruption might be fizzling to a close.

On Tuesday, they downgraded the alert level from orange to yellow and from "watch" to "advisory," just one notch above green and "normal." The last major explosion in the current eruption cycle occurred April 4.

"We aren't at the point where we can shut the lights off," said geologist Ryan Bierma. But the observatory has reduced its round-the-clock staffing in response to the continued decline of geologic activity at Redoubt, 100 miles southwest of Anchorage and across Cook Inlet from Kenai.

The small earthquakes that signal rising magma and surface rockfalls have dramatically slowed but are still above the background levels when Redoubt is restful, Bierma said. Significantly less gas is also passing through the volcano's vents, but that too is above normal, Bierma said.

Still, he and other scientists caution that the 2009 eruption isn't yet over and major explosions remain possible. The closest populated facility to the volcano -- the Drift River Oil Terminal about 22 miles away -- remains closed. Though workers have been conducting maintenance operations, no oil has moved since its tanks were drained of almost all crude in April.

Cook Inlet Pipeline Co. spokeswoman Lana Johnson said officials have not yet decided when to reopen the facility and how its operations will change. The tank farm and pumping station is a key link in the oil production system that starts with the offshore platforms on the west side of Cook Inlet. The platforms were forced to stop oil production, though some are producing natural gas.

"They're still trying to figure out what the long-term solution will be," Johnson said. "They are working on a solution that does not entail storing oil for any long time at the terminal."

None of the 50 or so workers directly employed by Cook Inlet were laid off, though some contract work was canceled.

After a 19-year lull, Redoubt erupted with a series of explosions on March 22. At least two of the explosions sent massive mud and water floods down Drift River and threatened the tank farm there. A dike built in response to floods from the 1989-1990 eruption held back the floods, but concern that it could be breached led officials to drain the crude into tankers.

Explosions from Redoubt also dropped ash on Anchorage, the Mat-Su Valley and on Kenai. Though aviation was severely disrupted, the ash had little effect on most other activities.

Since the last explosion April 4, a dome has been building from lava extruded through the volcano. Bierma said the surface of the dome has cooled so much that snow which fell Friday remained through the weekend.

In a statement issued Tuesday afternoon, the volcano observatory said that the dome may have stopped growing altogether. The most likely outcome is for continued decline in activity until Redoubt is once more at rest, the observatory said.

"Although it is considered less likely at this time, renewed explosive activity could also occur," the observatory warned.

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