Groans and steam emanated from Mount Redoubt yet another day, but the volcano showed no dramatic burst of energy, geologists noted Sunday.
"It looks like a volcano that wants to erupt, and our general impression is that it's more likely to erupt than not," said Tina Neal with the Alaska Volcano Observatory.
As a precaution, Elmendorf Air Force Base near Anchorage, about 100 miles northeast of Redoubt, was moving five C-17 cargo planes to McChord Air Force Base in Washington.
"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."
On Saturday, geologists observed 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.
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 signs of heat add to concerns that an eruption is near, which could send an ash cloud about 100 miles northeast toward Anchorage, the state's largest city, or onto communities on the Kenai Peninsula, which is even closer to the mountain on the west side of Cook Inlet.
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 before full eruption. Volcanologist Dave Schneider said seismic activity Friday was the most pronounced. 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."
Alaska's volcanoes typically erupt with blasts that can shoot ash 50,000 feet high.