Mount St. Helens' activity surprises scientists

VANCOUVER — The rock was at least the size of a man's head, and geologist John Pallister cradled it as he would a newborn — which, in a manner of speaking, it was.

As little as a month ago, this beefy slab was in liquid form, a pulsating 1,500 degrees Fahrenheit and working its way up from five miles below Mount St. Helens to form a chunk of the region's most active volcano.

For Pallister, a research geologist at the Cascades Volcano Observatory, evidence of how quickly Mount St. Helens is evolving doesn't get more solid.

"It's hard to believe that several weeks ago this was lava flow in the middle of the Earth," he said.

Four months after the volcano stirred back to life, drawing curiosity seekers from across the country, the bulging new oblong dome inside the crater has ballooned to 350 feet high, with nearly a 50-degree slope in places.

The dome now contains enough solid material to fill KeyArena more than 100 times. At the peak of the flow, molten magma was being transformed into new rock pushing skyward at a rate of 11 yards per day.

"It makes me think a lot differently about the range of possibilities for the future," Pallister said. "We were anticipating a different event.

"Figuring out what it means will take some time."

At 3:18 a.m. on Jan. 16, just 36 hours after geologists had walked along the surface of the new dome dodging vents emitting loud, hot blasts, a release of gas blew rocks and debris several hundred feet. It spread ash 8 inches or more thick inside portions of the crater and destroyed a few thousand dollars worth of instruments researchers had put there during their visit.

In its aftermath, the tremors at St. Helens have slowed, as the movement of rock creating the new dome slowed. As the sticky, newest sections of the dome are protruding, they are being scraped so hard against the existing surface they are turned white as the friction wears down its surface.

"We would have anticipated a different event," said Seth Moran, a U.S. Geological Survey seismologist.

Volcanologists would not have been surprised if there had been a significant rockfall, a continuing hazard as sections of the new dome jut higher and stretch more than a thousand feet to the side. The explosive release of gas suggested that St. Helen's plumbing is more finicky than first believed, that even slight changes in gas, or moisture below the surface, can trigger a new scenario.

"The question is, why now?" Pallister asked.

He wondered aloud if there was a more gas-rich flow farther below trying to push its way to the surface.

In fact, one of the most predictable things about Mount St. Helens has long been the volcano's unwillingness to act conventionally.

It's a reminder, said Jon Major, a research hydrologist at the observatory, that "we've learned an awful lot about what we don't yet understand."

Craig Welch: 206-464-2093 or cwelch@seattletimes.com