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Mount St. Helens' crater floor rising
Part of Mount St. Helens' crater floor has risen 50 to 100 feet since Tuesday while earthquake rates have been low, signs that magma is moving upward without much resistance, scientists said Thursday.
"The skids are greased," Jake Lowenstern, a U.S. Geological Survey volcanologist, said at a news conference at the Cascades Volcano Observatory in Vancouver, Wash.
With the latest rising, an area of the crater floor just south of the nearly 1,000-foot lava dome has risen about 250 feet since the mountain began stirring two weeks ago, Lowenstern said.
There's no way to tell when magma might reach the surface, he said.
On Wednesday, scientists lowered the alert level for the southwest Washington volcano, saying earthquake activity was down to the lowest level since before the mountain started venting steam last week.
U.S. Geological Survey scientists downgraded the "volcano alert" to a "volcano advisory," indicating the probability of an eruption that could endanger lives and property had decreased significantly since Saturday, when thousands of people were evacuated from the mountain.
Despite the new detail Thursday on the magma movement, scientists said there was no reason to raise the alert level back up.
Larry Mastin, a USGS expert in the physics of volcano eruptions, said that while there's an outside chance an eruption could send a plume of ash 15 miles into the air or higher, there is no indication that any eruption is imminent or that it would threaten lives or property.
Earthquake activity remained relatively low Thursday, with about one magnitude 1 quake a minute. The volcano was occasionally venting steam as water trickled down and hit hot rocks, Lowenstern said.
Scientists planned to make another flight over the volcano's crater Thursday to sample gas emissions and take thermal images, and to continue preparing instruments on the mountain for the winter.
A brief break in the clouds late Wednesday gave visitors a peek at weak steam emissions in the volcano's crater.
On Tuesday, under sunny skies, a spectacular cloud of steam and old ash rose thousands of feet above the 8,364-foot peak and a light dusting of gritty ash fell on some areas northeast of the mountain. It was the largest of a series of emissions of steam and ash since Friday.
Geologists continued to emphasize that there is little chance of anything similar to the blast that blew 1,300 feet off the top of the peak in May 1980, killing 57 people and paralyzing much of the inland Pacific Northwest with gritty volcanic ash.
Before then, Mount St. Helens had been silent since the 19th century.
The U.S. Forest Service reiterated Thursday that closures around the volcano — including the Johnston Ridge observatory five miles north of the crater — would remain in effect until authorities determine the area is safe. |
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