Mount St. Helens steams and swells

MOUNT ST. HELENS NATIONAL MONUMENT, Wash. - Mount St. Helens blew another cloud of steam skyward Thursday shortly after scientists said its crater floor had risen 50 to 100 feet since Tuesday, indicating that molten magma was moving upward without encountering much resistance.

A news helicopter hovering over the crater captured the latest venting, which sent gray and white clouds of steam billowing upward beginning about noon (3 p.m. ET).

Tom Pierson, a geologist with the U.S. Geological Survey, or USGS, told NBC News that no ash was in the release, attributing the darker colors of some clouds to the presence of magma near the surface, which made the steam appear darker.

The steam release came shortly after Jake Lowenstern, another USGS scientist, told reporters that “the skids are greased” for magma to reach the surface of the mountain’s crater.

Timing a matter of guesswork
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, adding that there was no way to tell when magma might reach the surface.

On Wednesday, scientists lowered the alert level for the volcano in southwest Washington, saying earthquake activity was down to the lowest level since before the mountain started venting steam last week.

USGS scientists downgraded the “volcano alert” to a “volcano advisory,” indicating that 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.

Larry Mastin, a USGS expert in the physics of volcano eruptions, said that while there was an outside chance an eruption could send a plume of ash 15 miles into the air or higher, there was no indication that any eruption was 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.

Flight over crater planned
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.

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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 was 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 closings around the volcano — including that of the Johnston Ridge observatory five miles north of the crater — would remain in effect until authorities determined that the area was safe.

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