July 29, 2004

ANCHORAGE, Alaska (Reuters) -- An Alaska volcano that last erupted 12 years ago, raining ash on the state's largest city, is now rumbling with earthquakes that may be a precursor to another eruption, scientists said Wednesday.

A series of shallow temblors that began in February beneath Mount Spurr, a volcano 80 miles west of Anchorage, are now numbering 15 to 20 a day, said officials at the Alaska Volcano Observatory.

"When we see an eruption, it commonly will start off this way," said Jackie Caplan-Auerbach, a seismologist at the observatory.

But it is also common for such sequential earthquakes beneath volcanoes to simply tail off, she said.

Seismologists will be looking for other possible signs of an impending eruption, such as gas or steam venting from the crater on the 11,070-foot peak, more frequent earthquakes or shallower earthquakes, which could indicate that magma was moving upward, Caplan-Auerbach said.

"We're officially keeping a much closer eye on it than we would if it were at background levels," she said.

In 1992, Mount Spurr's eruption sent an ash plume up 65,000 feet, disrupting air traffic.

The Alaska Volcano Observatory has classified Mount Spurr as deserving a "yellow" concern status, one step above the background "green" status.

Two other Alaska volcanoes are classified as subjects of elevated concern. Mount Veniaminof, a 7,073-foot volcano on the Alaska Peninsula and about 510 miles southwest of Anchorage, has been emitting small amounts of steam and ash since April. Shishaldin Volcano, a 9,372-foot peak in the eastern Aleutian Islands, has also been emitting ash.

Alaska has about 60 volcanoes that have been active in the past.

The Alaska Volcano Observatory is run by the U.S. Geological Survey, the University of Alaska Fairbanks and the Alaska Division of Geological and Geophysical Surveys.

Copyright 2004 Reuters.

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