Alaska volcano Mount Redoubt erupts

Alaska's Mount Redoubt volcano erupted four times overnight, sending an ash plume more than nine miles into the air, but the state's largest city has likely been spared from any ash fall.

"The ash cloud went to 50,000 feet, and it's currently drifting toward the north, northeast," said Janet Schaefer, a geologist with the Alaska Volcano Observatory.

The first eruption occurred at 10.38pm on Sunday night and the fourth happened at 1.39am today, according to the observatory.

The current wind patterns are taking the ash cloud away from Anchorage and instead heading toward Willow and Talkneetna, two communities near Mount McKinley, North America's largest mountain in Denali National Park.

Geophysicist John Power said no cities have yet reported any ash fall from the volcano, but noted that it's still early.

Using radar and satellite technology, the National Weather Service is predicting ash to start falling later Monday morning.

Dave Stricklan, a hydrometeorogical technician with the National Weather Service, expected very fine ash

"Just kind of a light dusting," he said. He said the significant amount of ash probably dropped immediately, right down the side of the volcano.

"The heavier stuff drops out very quickly, and then the other stuff filters out. There's going to be a very fine amount of it that's going to be suspended in the atmosphere for quite some time, but nothing to really affect anything such as aviation travel. The heavier stuff will filter out," he said.

The 10,200-foot (3,100-metre) Redoubt Volcano, roughly 100 miles south-west of Anchorage, last erupted during a four-month period from 1989-90.

But the volcano became restless earlier this year. The observatory had warned in late January that an eruption could occur at any time.

Increased earthquake activity over the past 48 hours prompted scientists to raise the alert level for Mount Redoubt yesterday.

Yesterday morning, 40 to 50 earthquakes were being recorded every hour.

A steam plume rising about 1,000 feet (300 meters) above the mountain peak was observed on Saturday.