Alaska's Mount Redoubt continued to rumble and emit steam Sunday but showed no dramatic burst of energy from the previous day, geologists monitoring the volcano said.
Geologist Tina Neal at the Alaska Volcano Observatory said scientists still believe an eruption is highly likely.
"It could erupt later today or in two weeks — or not at all," Neal said. "It looks like a volcano that wants to erupt and our general impression is that it's more likely to erupt than not. But there's still a possibility that this one could just go back to sleep. There's a lot of uncertainty."
As a precaution, Elmendorf Air Force Base near Anchorage — 100 miles northeast of Redoubt — was moving some of its aircraft to McChord Air Force Base in Washington.
Officials said the base was starting with five C-17 cargo planes and could relocate other aircraft if deemed necessary.
"We're just trying to be proactive and protect our assets," said 1st Lt. Erin Slaughter. "Our aircraft support other missions, such as delivering supplies to Iraq and Afghanistan, and this relocation will allow them to still do all those missions even if the volcano does erupt."
Flyovers by geologists Saturday found a quickly growing area of vigorous steaming at the 7,100-foot level on the north side of the mountain. Volcanic gas also was detected. No flyovers were conducted on Sunday.
Scientists on Saturday noted that a hole in a glacier clinging to the north side of the volcano had doubled in size since Friday, spanning the length of two football fields.
The area is just below a dome that formed the last time Redoubt blew in 1990.
The activity adds to concerns that Redoubt is close to blowing again. An eruption in December 1989 sent an ash cloud 150 miles that flamed out the jet engines of a KLM flight carrying 231 passengers on its way to Anchorage. Pilots were able to restart the engines and land safely.
The observatory last week detected a steep increase in earthquake activity below the volcano, upgrading its alert level to orange, the stage just before full eruption. Volcanologist Dave Schneider said seismic activity on Friday was the most pronounced, shaking constantly.
Since then, activity has been less intense and more intermittent, but still far above normal for Redoubt.
"Volcanoes are kind of like kids. Each has their own personality, their own levels of seismicity," Schneider said. "Redoubt is pretty much above any volcano's seismicity. It's a very restless volcano at present."
The warning that the volcano was likely to blow prompted a rush on dust masks and car air filters in Anchorage as well as closer communities.
Alaska's volcanoes typically start with an explosion that can shoot ash 50,000 feet high and into the jet stream, but there are warning signs because magma causes small earthquakes as it moves.