St. Helens erupts politely, hints show may get livelier

By Sandi Doughton
Seattle Times staff reporter

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After 2½ weeks of rumbling, burping buildup, lava finally punched through to the surface at Mount St. Helens early yesterday.

But it happened so quietly even scientists didn't realize it at first.

Only after infrared instruments revealed that a fin of rock the size of a six-story apartment building registered nearly 1,100 degrees did geologists conclude it was made up of partly hardened lava.

"The fact that we see stuff at the surface that hot means it's new rock," said U.S. Geological Survey volcanologist Willie Scott.

The fin appeared on a new dome that has grown nearly 400 feet tall as magma pushed up against the crater floor.

Unlike the red, runny streams of lava that pour from Hawaiian volcanoes, lavas from Mount St. Helens are typically so thick, blocky and slow-moving that they can be hard to distinguish from existing rocks, Scott said.

But if the volcano continues to produce lava flows, the spectacle could improve.

"If we get a good extrusion like we had in the '80s, there will be a lot of glow as this hot stuff starts breaking apart at night and the blocks crash down the side of the dome," Scott said. "And if it were to snow or rain now with stuff at such high temperatures at the surface, there would be a lot of steaming going on."

During the six years following its catastrophic 1980 eruption, Mount St. Helens produced a stream of small eruptions, steam explosions and lava flows that built up a 925-foot dome on the floor of the blasted-out crater.

Scientists don't know if the current episode will last that long.
 
"It's possible this new feature will enlarge and perhaps even dwarf the old dome," said USGS geologist Tina Neal. "We can't really say at this time."

The mountain could still produce moderate-sized, explosive eruptions that could spread ash over surrounding communities and unleash mud flows, though not big enough to threaten any towns or structures, added USGS geologist Jon Major.

"We expect to see more magma coming to the surface, but that doesn't mean we won't see explosive activity in the future," he said.

Geologists call molten rock "magma" when it is underground and "lava" when it reaches the surface.

For now, magma in the volcano's plumbing seems to be moving without significant obstruction, as reflected by a drop in earthquake activity.

Tiny tremors measuring just above zero on the magnitude scale continue to shake the mountain several times each minute, said University of Washington seismologist Steve Malone. Magnitude 1 earthquakes are occurring at a rate of about one every five to 10 minutes, a sizable drop from two weeks ago, when magnitude 2 and 3 quakes were hitting several times a minute, and the volcano released three small steam and ash eruptions.

"One interpretation is that the system is so well greased now that the magma can move easily," Malone said.

An explosive eruption could occur if the magma's path is blocked again, allowing gas to build up underground, then break through with a big bang. An explosion could also result if volatile, gas-rich magma rushes to the surface, Scott said.

"That could create a runaway situation."

But because there is still no evidence of large-scale magma migration into the volcano, scientists don't expect anything close to the 1980 eruption, which killed 57 people and leveled forests for miles around.

However, it's important to keep monitoring the volcano for any changes that could signal more severe eruptions, Scott said.

To help out during bad weather or darkness, when manned aircraft can't fly over the mountain, a Tucson-based company has offered to let scientists use an unmanned drone, mounted with instruments.

The Federal Aviation Administration hasn't approved the plan.

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com

The Associated Press contributed

to this report.