Mount Redoubt has shifted into a different pattern, emitting a more steady ash plume rather than the violent explosions of the past week, scientists said Monday.

Federal and state officials also have established a unified command to address the volcano's impact on an oil storage facility holding more than 6 million gallons of oil.

The volcano 100 miles southwest of Anchorage has erupted 18 times since March 22, sending ash in various directions. A light dusting of ash fell for the first time on Anchorage on Saturday.

But since then, the volcano has entered a new phase, according to monitors at the Alaska Volcano Observatory.

"In the past 12 hours, we've had frequent, low-level ash emissions," seismologist Stephanie Prejean said.

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Think of it as a steady ash plume for the most part, Prejean said, but emissions generally have not risen above 20,000 feet and have not reached large population centers.

One spike Monday morning took the ash to 27,000 feet, and that prompted Alaska Airlines to temporarily suspend flights in and out of Anchorage because of the damage ash can do to engines.

Airline spokesman Paul McElroy said ash conditions are constantly being monitored and the flight schedule reassessed for current conditions.

"We will continue to fly as long as it's safe to do so," he said as flights were being resumed following the two-hour flight suspension.

Scientists say they can't predict how long Redoubt stays in this mode.

"It could continue for some time, but this is also a very unstable system so we could also go back to seeing these large explosions," Prejean said.

The Coast Guard, the Alaska Department of Environmental Conservation and private company Cook Inlet Pipeline Co., have established the unified command over concerns with the Drift River oil terminal, 23 miles from the volcano.

Officials have said a $20 million berm built after the 1989 eruptions of Mount Redoubt is holding against flooding and mud slides created by the eruptions.

Gary Folley, the DEC's onsite coordinator, said the department is concerned about the threat the oil poses to Cook Inlet "if nature does get the best of the situation and there is a spill."

He said the quickest way to eliminate that threat is to remove the oil from the tanks, if it can be done safely.

But, he said, that was easier said then done.

If oil were to be removed, not all could be suctioned out, leaving more than 1 million gallons in the tanks.

And if it is removed, the tanks would weigh less and be more buoyant and susceptible to flooding if the containment layers were breached.

"We don't want to create a situation that is riskier than what we have now," he said.

The Coast Guard and the U.S. Army Corps of Engineers were at the oil terminal on Monday to assess conditions.

For the oil to be off-loaded, it would have to be done with a tanker, said Coast Guard Cmdr. Jim Robertson. But the safety of the crew and vessel is paramount.

He said a tanker is scheduled any time between April 4 and April 6, and the unified command is working with the tanker company to establish a plan to minimize any risk associated with removing the oil.

"We're not going to bring a tanker in until it's safe to do so, until we have a plan to properly and safely move that oil and mitigate the risk," he said.

But right now, officials said, the safest place for that oil is in the tank.

Several Alaska House Democrats also have written the commissioners of the Fish and Game and Environmental Conservation departments expressing their concern about the oil storage facility and asking to be updated on future plans.

"It's now obvious, and has been for a long time, that the existence of West Cook Inlet's main crude oil storage facility in a volcanic floodplain poses a danger to one of the state's most important fisheries," the letter says.

U.S. Sen. Lisa Murkowski, R-Alaska, on Monday said she would introduce a bill to establish a national volcano monitoring system, which would include the Alaska Volcano Observatory and four other sites.

Murkowski's bill would establish a National Volcano Early Warning and Monitoring System within the U.S. Geological Survey to monitor and warn citizens about volcanic activity. The program would be funded at $15 million annually.

The other four observatories are in Washington state, Hawaii, Yellowstone National Park and California.