Mount Redoubt went from boiling to simmering Wednesday, leading scientists to lower the alert level for the Cook Inlet volcano from "warning" to "watch" and the aviation risk from red to orange.
"The seismic activity has really declined," said Chris Waythomas, a hydrologist on watch duty at the Alaska Volcano Observatory in Anchorage. "Things are very quiet."
Meanwhile, bad weather forced postponement of an engineering assessment of the dike protecting the Drift River oil terminal from potential flooding caused by melting of ice fields and glaciers from the volcano. An eruption-caused flood Monday was contained by the two-mile dike, but officials want to make sure the concrete-shielded, earthen structure wasn't damaged and is still capable of doing its job in the event of another flood.
The observatory relaxed the alert level at 1:35 p.m., just hours after two mild eruptions Wednesday morning that produced only a trace of ash. If Redoubt follows its own historic patterns, it will continue to erupt periodically for the next several months before quieting down, they say.
Waythomas said the volcano may be building a lava dome. That's what happens in volcanoes like Redoubt when molten rock rising from deep within the earth hardens into an unstable structure at the surface. At this stage in its cycle, the dome can be expected to collapse, producing ash and hot gasses in the process. Before that happens, seismic activity would likely increase, leading to a higher alert advisory, Waythomas said.
Ash is abrasive and dangerous to lungs and machines and, carried by winds, can affect communities hundreds of miles away.
Redoubt, across the Inlet from Kenai and about 100 miles southwest of Anchorage, is upstream from the Drift River terminal, where 6 million gallons of Cook Inlet crude is currently in storage. The Cook Inlet Pipeline Co. facility, managed by Chevron, was evacuated Monday after the first series of eruptions from Redoubt about 20 miles away.
The facility sits in the river's floodplain and was flooded in the last eruption cycle, from 1989 to 1990. The dike was completed in August 1990.
Normally, the terminal stores oil for Chevron and other producers until enough is on hand to fill a tanker. With operations at the Drift River suspended, oil is being stored at two other west Cook Inlet facilities, Trading Bay and Granite Point.
In a statement Wednesday, Cook Inlet Pipeline said it was hopeful about resuming operations.
"Plans are also under way to resume operations to receive, store and transport oil as soon as it is safely possible," it said.
That's not what the environmental organization Cook Inletkeeper would have the company plan. Bob Shavelson, the group's executive director, said he is standing by a demand made Tuesday that Chevron drain the tanks to prevent the possibility of a massive oil spill if a cataclysmic flood of meltwater and mud roars down the Drift River as it did 20 years ago. No oil was spilled then, but the river changed its course at least once.
Gary Folley of the Alaska Department of Environmental Conservation's Soldotna office, the state's chief oil-spill watchdog in the Kenai area, said he didn't believe Drift River operations will resume anytime soon.
"They can't. There's certain things they have to do to ensure the integrity of the pipeline, and they need to be able to get a tanker safely into the platform," Folley said. "It's nothing they can rush into."
But Folley also said there would be no need to drain the tanks as long as the dike remained in good shape.
The morning explosions Wednesday did not produce significant amounts of ash, the volcano observatory reported.
The last event, at 10:17 a.m., was the eighth explosion since Redoubt began erupting Sunday evening. It followed an earlier, similar explosion at 5:12 a.m.
The height of the ash cloud from the early blast was estimated to be about 15,000 feet, but it appeared to have dissipated over the volcano, the National Weather Service reported.
"It was such a minor eruption, we almost didn't see it on the radar," Weather Service meteorologist Christian Cassell said.
The 5:12 a.m. eruption lasted about 10 minutes.
"This is in a different class compared to the other six -- it's quite a bit smaller," Alaska Volcano Observatory geophysicist Peter Cervelli said.
Seismometers positioned around the volcano began sending a stronger signal about 10 minutes before the eruption, he said.
Darkness and bad weather precluded visual observation of the explosion through the AVO webcam, but radar detected the ash cloud, Cervelli said.
"Our best guess is we're extruding a lava dome and we may have had a piece of that dome break off and tumble along and produce an ash cloud," he said.
Daily News reporter George Bryson contributed to this story.