Wednesday, April 01, 2009

Alaska: Lava dome could cause eruption

Geologists said Tuesday that a dome was building in Mount Redoubt's crater, which could collapse and trigger another eruption.

"The difficult thing with these dome-building eruptions -- it is very difficult to give short-term warning because these things can go unstable and fail very quickly, putting an ash plume up to significant heights," geophysicist Stephanie Prejean said.

When a similar dome-building episode occurred on Redoubt in 1989 and 1990, the mountain erupted some 20 times, according to geologists with the Alaska Volcano Observatory.

Their best guess: Redoubt is not finished yet. The AVO says it is now clear magma has reached the surface, and that's what is contributing to the dome-building in Redoubt's crater.

Some of the ash samples they collected Tuesday from the Drift River Valley contained pumice, which also indicates magma has found its way to the surface.

Geologists got their first good look at the area around Mount Redoubt on Tuesday, more than a full day after the volcano began erupting late Sunday night with the first of six violent explosions.

The most recent eruption came at about 7:41 p.m. Monday, and mudflows have surrounded a Cook Inlet oil terminal, which had to be evacuated.

The eruptions scattered ash across a wide swath of the Susitna Valley, but evidence of the eruptions is more dramatic on the mountain's flanks.

In a flight over the area Tuesday, officials with the Alaska Volcano Observatory couldn't see Redoubt's summit -- but they could see the eruptions' fallout, starting high on the mountain on the Drift Glacier.

"There was a huge flow of muddy water cascading down the middle of the Drift Glacier, cutting a deep channel in the glacier with some really impressive waterfalls," AVO research geologist Kristi Wallace said. "So this is really muddy, sediment-laden water."

From the glacier the mudflows swept through the Drift Valley, uprooting some trees and stripping others of limbs and bark. The flows, a mile wide in some spots, continue on to Cook Inlet.

As of 11 p.m. Tuesday, there were no ash fall advisories in effect and flights in and out of Ted Stevens International Airport remained unaffected. But with more eruptions a strong possibility, that all remains subject to change.

Ash has primarily scattered to the north of Redoubt and has been reported as far north as Healy near Denali National Park, and even Delta Junction.

Contact Jason Moore at

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