Lava breaks surface at Mount St. Helens

By Sandi Doughton
Seattle Times staff reporter and The Associated Press

DON RYAN / AP A steam plume colored by the sun rises above the crater of Mount St. Helens yesterday. "The steam plume is essentially a constant feature that will be there for days to come," geologist Willie Scott said.

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This morning, scientists reported a piece of solidified lava protruding from the dome that has been building in the volcano's crater. Infrared instruments measured the temperature of the new rock at 900 to 1100 degrees, said U.S. Geological Survey geologist Tina Neal.

"That's hot enough to be incandescent and glow," Neal said. However, the glow would probably only be visible at night, she added.

Lava from Mount St. Helens is typically very thick and blocky, and can be difficult to distinguish from ordinary rock except by taking its temperature. "It's not like the runny red lava you see in Hawaii," Neal said.

Steam explosions will probably continue as glacial ice melts and comes into contact with the hot rock.

A larger, explosive eruption is also still possible.

"Just because we see lava at the surface doesn't mean we won't see explosive activity in the future," said USGS scientist Jon Major.

But even if that happens, the worst impact to surrounding communities would be a thick cloud of volcanic ash, Major added. While an explosive eruption could pulverize and melt a portion of the glacier in the volcano's crater, the resulting mud flows would not be large enough to threaten any towns or structures.

"We've gone through scenarios to come up with the maximum credible event that could come out of the crater, and the largest one we've considered ... dies out in the valley by the time it reaches the sediment retention dam" on the North Fork of the Toutle River, Major said.

For several days, scientists have known that magma was close to the surface in the crater, where the nearly 350-foot bulge has appeared.

The bulge sits just south of the large dome that was built up during a similar period of eruptive activity after Mount St. Helens catastrophic 1980 eruption.
 
"It's possible this new feature will enlarge and possibly even dwarf the old dome," Neal said. "We really can't tell at this time."

Scientists had known for days that magma or molten rock was nearing the surface, as the bulge grew.

Seismic activity has dwindled to small quakes, about magnitude 1, every five to 10 minutes, Neal said. That suggests smooth, steady magma flow to the new dome, she said.

The mountain exploded on May 18, 1980, with a massive landslide as the top of the mountain collapsed. Any new ash eruption, scientists say, would likely be much smaller and would shoot vertically, instead of the devastating horizontal blast in 1980 that left 57 people dead, leveled trees for miles around and covered much of the Pacific Northwest with ash.

For the past week and a half, the restless mountain has sent steam, sometimes mixed with ash, venting from the bulge on the lava dome that has risen at least 330 feet since scientists noticed it Sept. 30.

The mountain in the Cascade Range rumbled back to life Sept. 23, beginning with thousands of tiny earthquakes. For five days earlier this month, it spewed clouds of steam mixed with small amounts of old volcanic ash.