Mount Redoubt, shown steaming on March 15, erupted four times starting Sunday night. (U.S. Geological Survey, Heather Bleick/Associated Press)

Eruptions at Alaska's Mount Redoubt volcano have sent a plume of smoke nearly 15,000 metres above sea level.

Geologists at the Alaska Volcano Observatory said the volcano erupted five times late Sunday and early Monday.

"This is a fairly large eruption, close to the larger cities in Alaska," said geophysicist John Power.

The first eruption occurred at 10:38 p.m. on Sunday night and resulted in about four hours of continuous volcanic tremors.

Seismic activity around the volcano had been intense in recent days, geologists said, and it was expected that the volcano would blow. Up to 50 earthquakes per hour were being reported in the area on Sunday prior to the eruption.

Mount Redoubt, which is about 160 kilometres southwest of Anchorage and stands at 3,108 metres, last erupted over a four-month period in 1989-90, Power said.

The Alaska Volcano Observatory issued a red alert for the region, indicating that an eruption is underway and that a significant amount of volcanic ash is in the atmosphere.

The observatory said the eruptions appear to be caused by a steam explosion in a shallow hydrothermal system of the volcano. It is still unclear if the eruptions represent a flow of new magma or pulverized old material.

More explosions expected

John Power, a geophysicist with the U.S. Geological Survey Alaska Volcano Observatory, shows a satellite image of the eruption of Mount Redoubt. (Al Grillo/Associated Press)

The observatory said that more explosions are expected with little to no warning — and will contain more volcanic ash.

The seismic activity at Mount Redoubt could continue for weeks or months, the observatory said.

The observatory is staffing its offices 24 hours a day during the activity at Redoubt and has opened an operations centre in Anchorage.

The ash fall from the eruptions is currently drifting northeast and will likely not fall onto Anchorage, said Janet Schaefer, a geologist with the Alaska Volcano Observatory.

But wind patterns are sending the ash cloud toward Willow and Talkneetna, which are near Mount McKinley in Denali National Park.

The U.S. National Weather Service is predicting that fine ash fall will start in several communities late Monday morning.

Volcanic ash consists of tiny jagged pieces of rock and glass that are mildly corrosive and conduct electricity when wet. The ash can also injure skin, eyes and breathing passages.

Clouds of the ash can turn daylight into complete darkness and are often accompanied by rain and lightning that can result in power outages and communication interruptions. The ash is also a problem for airplanes.

Flights cancelled

Alaska Airlines on Monday cancelled 19 flights in and out of the Anchorage International Airport because of the ash.

Elmendorf Air Force Base in Anchorage told only essential personnel to report to work. The air force said 60 planes, including fighter jets, cargo aircraft and a 747 commercial plane, were being sheltered.

Residents in the area also being asked not to drive.

But most of the debris from the eruption appears to have dropped down the side of the volcano, said Dave Stricklan, a hydrometeorogical technician with the weather service.

"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," Stricklan said.

Light ash fall has been reported in Skwentna and the Susitna Valley, according to the weather service.

"It's coming down," said Willow resident Rita Jackson. "My eyes are itching really bad."

People living in the affected areas are being advised to seal windows and doors and cover air and water intakes in their homes.

With files from the Associated Press