for National Geographic News
Mount St. Helens may continue its current slow eruption for decades, eventually rebuilding the dome that was blasted away when the volcano erupted in 1980, according to a geologist.
But the volcano, located in Washington State, could also stop erupting today (see Washington State map).
Daniel Dzurisin with the Cascades Volcano Observatory in Vancouver, Washington, is one of many scientists trying to understand when Mount St. Helens's most recent eruption, which began in October 2004, will end.
Several lines of evidence, he said, suggest the volcano's magma chamber a few miles below the surface is consistently resupplied with magma from an even greater depth.
If so, Mount St. Helens could keep erupting for decades or even centuries, in a so-called open system.
However, if the system is closed, the volcano's magma chamber will eventually be depleted, and the eruption will end.
Ample evidence for this scenario also exists, Dzurisin said.
"There's no compelling reason to choose one [scenario] over the other," he said.
If Mount St. Helens is a closed system, Dzurisin said, the reservoir of magma underneath it would decline over time, causing the volcano to sink and the land around the volcano to move in toward the volcano.
(See an interactive feature on how volcanoes work.)
"It would be like having a balloon buried in the sand and you take air out of the balloon and let it come up through a straw and go to the atmosphere," he said.
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