Break in clouds allows check of volcanic burst

SEATTLE – In its latest explosion, Mount St. Helens blasted rocks and ash from the north end of its still-growing lava dome, sending a dusting of ash nearly two miles from the crater of the southwest Washington volcano.

But since that all happened at about 3 a.m. Sunday, nobody saw the 17-minute “explosive emission,” said hydrologist Carolyn Driedger of the U.S. Geological Survey at the Cascades Volcano Observatory in Vancouver, about 50 miles from the peak.

Scientists knew something had happened because the blast knocked out new instruments they had placed inside the crater just two days earlier.

“This is the kind of event that we knew could happen,” Driedger said Friday. “We have this relatively placid dome-building ongoing since October, but we recognize that we can have these small explosions.”

Taking advantage of a break in the clouds Wednesday, scientists took photos and checked out the latest event in the volcano’s eruptive phase that began last fall.

Blocks of rock blasted from the vent could be seen embedded in the snow, Driedger said, estimating they were about 1 foot across. But scientists didn’t want to get too close.

“We haven’t been inside the crater to look for sure,” she said.

Ash fell thickly in east and west parts of the crater and drifted eastward over the rim, leaving a thin layer of gray ash on the east flank, the USGS said.

The explosion was similar to an Oct. 1 blast that was clearly visible, the USGS said. The volcano spewed clouds of ash and steam for five days, and molten rock began reaching the surface later that month, oozing out and building a new lava dome inside the crater.

The new dome has continued to grow but at a slower rate than last fall, the USGS said. Since Dec. 11, it has grown 100 meters or 330 feet in width, and 7 meters or 23 feet in height at its tallest point. It has remained 475 meters or 1,566 feet in length, constrained by the old lava dome and crater wall.

Low-level earthquakes, emissions of steam and gas, and ash production have continued.

Driedger said scientists are “not forecasting, we’re just making observations ourselves.”

The massive May 18, 1980, eruption of the volcano 100 miles south of Seattle blew the top 1,314 feet off the 9,677-foot peak, killed 57 people and covered the region with gritty ash.