Anchorage - Geologists on Saturday spotted expanded holes in the glacier that clings to the north side of Alaska's Mount Redoubt, and rivulets of water streaming down its side, as they closely monitored the volcano for a new eruption.

Scientists with the Alaska Volcano Observatory on Friday flew close to Drift Glacier and saw vigorous steaming emitted from a football field-size area on the north side of the mountain. By Saturday, they had confirmed the area was a fumarole, an opening in the earth that emits gases and steam, and that it had doubled in size overnight.

The area is at 7,100 feet, just below a dome that formed the last time Redoubt blew in 1990, said research geologist Kristi Wallace.

Observers also saw water streaming down Drift Glacier, indicating heat from magma is reaching higher elevations of the mountain.

"The glacier is sort of falling apart in the upper part," Wallace said.

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 are even closer to the mountain on the west side of Cook Inlet.

Particulate sent up in an eruption has jagged edges and can injure skin, eyes and breathing passages, especially in young children, the elderly and people with respiratory problems.

It can also foul engines. An eruption in December 1989 sent out an ash cloud 150 miles that flamed out the jet engines of a KLM flight carrying 231 passengers on its way to Anchorage. The jet dropped more than two miles before pilots were able to restart the engines and land safely.

The volcano observatory a week ago detected a sharp increase in earthquake activity below the volcano and upgraded its alert level to orange, one stage below red for a full eruption. The warning that an eruption was imminent prompted a rush on dust masks and car air filters in Anchorage.

Wallace flew Friday and observed other indications of warmth on the nearly 10,200-foot mountain. At a flat area on the 9,000-foot level, scientists photographed a "collapse feature," a circular hole where ice had melted. The feature had grown larger and become irregular in shape by Saturday, Wallace said.

"That tells us that there's some indication that a magma chamber is moving up into the volcanic edifice and heating up the rocks," Wallace said.

Scientists flying into or near the plume Saturday took samples of sulfur dioxide, hydrogen sulfide and carbon dioxide, all magmatic gases, Wallace said.

Alaska 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.

Geologist Jennifer Adleman said magma is a combination of three phases: liquid rock plus a gas and crystals than can form sort of a froth that works its way up the mountain.

"A lot of scientists refer to is as a crystalline mush," she said.

The hot liquid and the gas fracture rock as they create a path and force their way to the surface. The observatory has been recording quakes up to magnitude 2.1 but not at the frequency that preceded the 1989 and 1990 eruptions.

"We're looking for an increase of seismicity to match the precursor activity," Wallace said. "We haven't seen that yet."

The observatory is a joint program between the U.S. Geological Survey, the University of Alaska Geophysical Institute and the state Division of Geological and Geophysical Surveys.

If the mountain erupts, the observatory will immediately alert the Federal Aviation Administration to warn pilots, and then other emergency officials.