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Magma certainly surging toward the surface
Magma: The molten rock remains as enigmatic as it is volatile, despite the reach of science and technology
Tuesday, October 05, 2004
MICHAEL MILSTEIN
As earthquakes continued while the volcano vented Monday, evidence piled up that the culprit driving Mount St. Helens' behavior is the superhot molten rock known as magma.
Magma's path and ways are mysterious. But geologists Monday said magma was certainly surging toward the surface at the mountain, shoving a dome in the crater up and fueling spectacular blasts of steam over the past few days. Eventually, they say, Mount St. Helens will probably erupt an explosive brew of lava, rock and ash.
For all the high-tech sensors that ring the mountain, researchers remain unsure just how far the magma has risen and how fast it's moving.
"Sometimes you don't know until after it's erupted or after you have many examples to go by," said Wendy McCausland, a doctoral student at the University of Washington who has studied Mount St. Helens and other volcanoes.
Tracking magma is like trying to see what's happening behind a wall. Scientists must rely on the sounds it makes and the earthquakes it triggers as it busts through rock and emits gases.
But the symptoms that suggest magma's menacing arrival are not consistent.
Most earthquakes beneath Mount St. Helens have been within roughly a mile of the surface -- shallow by geologic standards. But carbon dioxide gas wafting from the crater suggests the magma has come from greater depths -- and such magma, "fresher" and containing more gases, can be far more explosive.
A few steady and sustained tremors -- like the hum of organ pipes -- also suggest magma rising through a vast subterranean plumbing system. However, it's difficult to tell precisely where it's coming from.
"Usually we rely on what we're seeing at the surface to tell what it means," McCausland said.
The first clear seismic footprint was the shallow earthquakes.
"Often times, the first time it shows up seismically is relatively shallow, yet we know it's come from greater depths," said Paul Wallace, an assistant professor at the University of Oregon. "Sometimes it just mysteriously appears."
It may be that some of the magma has risen from depths so hot and soft that rocks might bend rather than break as it forces its way past.
"It's hot and it's plastic and it's goopy, so you don't really know about it until it hits a cap that's harder and more brittle," said Edward Wolfe, a U.S. Geological Survey researcher who studies Mount St. Helens.
Magma begins roughly 60 miles beneath the surface, where the Earth's crust slides from beneath the Pacific Ocean under North America and then melts. It rises to feed volcanoes such as St. Helens, pooling in spots, like balloons against a ceiling, before working its way higher.
The speed of earthquake waves rippling through the ground and the chemical makeup of St. Helens magma, suggest a pond of magma roughly five to nine miles beneath the surface. A bottleneck of cooler, harder rock may separate it from smaller ponds of magma higher in the volcano's plumbing.
It's not clear precisely how or why magma forces past that bottleneck.
But how it emerges may depend on how long it waits underground.
Lava flowing in tranquil streams from volcanoes in Hawaii rises fast, hot and fluid.
Mount St. Helens can be more explosive. Its magma comes thicker and frothy with gas. It may move slowly enough, its gas bleeds off until lava simply oozes out, said U.S. Geological Survey scientist Christopher Newhall. Or it may shoot out like a shaken champagne bottle that's suddenly uncorked.
The mountain's catastrophic 1980 eruption probably released enough energy that a repeat is unlikely soon, scientists say.
Eruptions in coming days and weeks, scientists say, probably will resemble those that built the mountain's dome later in the 1980s. Rushing flows of hot ash may appear with such blasts but are unlikely to endanger people.
Final proclamations, however, are not possible until the magma shows up.
Michael Milstein: 503-294-7689;
[email protected]
..). It sure was very exciting and scary, but sweeping up the 3 inches of ash every day soon got old! 
