Crater's "Loaf" rises 100 feet on St. Helens

By Hal Bernton
Seattle Times staff reporter

GREG EBERSOLE / THE (LONGVIEW) DAILY NEWS Surrounded by clouds, steam is seen venting out of three locations inside the crater of Mount St. Helens yesterday. Part of the floor of the crater has risen 100 more feet, and scientists are calling this uplifted area "the Loaf.

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Scientists call this uplifted area "the Loaf." It is a fractured zone that underlies glacier ice and part of the crater's lava dome, and it now has risen a total of about 250 feet in the past week, according to the U.S. Geological Survey.

Scientists say the deformity is caused by pressure from magma that is fitfully working its way toward the surface and a probable eruption. They say all the events of the last two weeks — earthquakes, harmonic tremors, ash explosions and steaming inside the crater — are likely leading up to such an event.

But, despite the Loaf's new growth and another belch of steam from vents in the crater about 9:30 a.m. yesterday, the alert for the volcano remained at Level Two on a three-point scale. That means scientists don't think lives or property are in immediate peril.

A substantial drop in earthquake activity prompted scientists to speculate Wednesday that the magma had taken a temporary pause in its rock-breaking journey to the surface.

But the Loaf's expansion, detected in overflights later that day, appeared to indicate that magma is still on the move, perhaps with a pathway cleared at least partially by three steam and ash explosions over the past week.

"The skids are greased," said Jake Lowenstern, a USGS volcanologist. "It certainly seems like the volcano has found a weak area to push up."

Just how deep the magma lies is a matter of speculation. Some scientists think it could be right under the lava dome, while others think it could be more than several hundred meters down.

Scientists also have debated whether a future eruption would be a relatively quiet event, with magma simply oozing into the crater, or a more explosive event with the potential to throw ash tens of thousands of feet into the air.

Under some circumstances, ash from such an eruption could reach populated areas and interfere with aviation.

Yesterday, Larry Mastin, a USGS official, said most scientists now think there will likely be a mix of both kinds of events: "The question is, what size will they be?"
 
Mastin said a moderate explosive eruption now appears quite possible, and there is a small but significant chance of a larger eruption that could fling ash 15 miles into the sky. Such an eruption also could cause super-heated rocks to race down the mountain on cushions of gas, a phenomenon known as a pyroclastic flow.

It also could cause mudflows, known as lahars, that could reach the North Fork Toutle River. But USGS and Army Corps of Engineers officials said yesterday that a downstream sediment-retention dam built in the 1980s would help slow the flows, so they would not threaten downstream communities.

All the scientists who have briefed reporters in recent days have stressed that there are no signs of any deformation on the flanks of the mountain similar to the bulge that formed before the catastrophic May 18, 1980, eruption.

Without such a bulge, they say, the mountain is not at risk of repeating that day's landslide and deadly sideways explosion that claimed 57 lives.

"We're not going to see a lateral blast this time," Mastin said.

Meanwhile, U.S. Agriculture Secretary Ann Veneman took an aerial tour of the Mount St. Helens area yesterday. Her department includes the U.S. Forest Service, which manages the lands around the volcano.

Seattle Times staff reporter Ian Ith contributed to this report from Vancouver, Wash. Hal Bernton: 206-464-2581 or hbernton@seattletimes.com