Trouble brewing at Mount St. Helens

MOUNT ST. HELENS NATIONAL MONUMENT, Wash. — Government scientists raised the alert level Saturday for Mount St. Helens after its second steam eruption in two days was followed by a powerful tremor. They said the next eruption was imminent or in progress, and could threaten life and property in the remote area near the volcano.

Hundreds of visitors at the building closest to the volcano — Johnston Ridge Observatory five miles away — were asked to leave. They went quickly to their cars and drove away, with some relocating several miles north to Coldwater Ridge Visitors Center, which officials said was safe.

The volcano alert of Mount St. Helens was raised to Level 3, which "indicates we feel an eruption is imminent, or is in progress," said U.S. Geological Survey geologist Tom Pierson from the observatory. He said Saturday afternoon that an explosion probably would happen within the next 24 hours.

Pierson said the volcano has released more seismic energy since quake activity began Sept. 23 than it has at any point since its devastating May 18, 1980, eruption, which killed 57 people and coated much of the Northwest with ash. But scientists expect the impending eruption to be much smaller than the 1980 blast.

A day after the volcano spewed a plume of steam and ash thousands of feet into the air, there was a very brief steam release Saturday — a puff of white cloud, followed by a dust-raising landslide in the crater. A volcanic tremor signal that came next was what prompted the heightened alert level.

The signal "was far stronger after today's steam eruption" than the tremor that followed Friday's blast, Steele said. "We were picking it up throughout western Washington and into central Oregon. Yesterday we had a very weak tremor signal."

A tremor — a steady vibration — "indicates movement of gases or fluid within the volcano," Steele said, while individual earthquakes indicate "a pounding and breaking of rock."

Saturday's tremor lasted about an hour before it was drowned out by a series of earthquakes — one or two a minute.

Interior Secretary Gale Norton, who flew over the mountain Saturday, said the seismic activity has weakened the 1,000-foot lava dome that began forming in the volcano's crater after the 1980 eruption.

Norton said the chances of an eruption or lava flow have increased, and that the volcano most likely will see moderate ash eruptions.