Friday, March 11, 2011

"Sleeping" Volcanoes Can Wake Up Faster Than Thought

The Soufriere Hills volcano.The Soufrière Hills volcano erupts on Montserrat in January 2010.

The world's "sleeping giants" can wake up much quicker than thought, according to a new volcano model.

Scientists believe the magma chambers—or reservoirs of molten rock—under dormant volcanoes are filled with sticky, viscous mush.

For a volcano to "wake up," this mush needs to be thoroughly heated by fresh, hot magma rising up from the deep Earth.

According to current theory, it would take several hundred or perhaps a thousand years for the heat to distribute through the chamber and make the magma fluid enough to erupt.

But a new model based on fluid dynamics shows that hot, deep magma can mix with the older, sticky stuff much easier than believed, scientists say.

"That's one reason that the rejuvenation can happen so quickly—the transport of hot material coming in [to the] magma system is much more efficient than we previously had understood," said study co-author George Bergantz, a geologist at the University of Washington.

The team compared their model with two real-life eruptions: the Philippines' Mount Pinatubo in 1991 and an ongoing eruption of the Soufrière Hills volcano (picture) in the British Caribbean territory of Montserrat (see map).

The scientists analyzed the two volcanoes' magma temperatures, chamber sizes, and other physical features to come up with rough time intervals between the first warning signs and the actual eruptions.

In the case of Pinatubo, the team discovered that the magma chamber took only 20 to 80 days to reactivate, versus the 500 years predicted by conventional theory.

Still, the model doesn't suggest reawakened volcanoes are more likely to cause dangerous eruptions, Bergantz cautioned.

"I don't think it really changes our take on that," he said. "Many of the hazards associated [with a dormant volcano waking up] are more related to landslides than eruption processes."

Likewise, a reheated magma chamber doesn't always lead to an eruption, the study authors noted.

The new study should bring more attention to supposedly resting volcanoes, said Michael Petronis, a geologist at New Mexico Highlands University in Las Vegas, New Mexico, who was not involved in the research.

In general, "whether or not a volcano is actually dormant is up for discussion," Petronis said.

"If this model works, and you can rejuvenate a magma chamber by a pulse of magma, you can kick off an eruption when you weren't expecting it."

Mount Pinatubo, for example, had never erupted in recorded history before it stirred to life in 1991, killing at least a thousand people. ...

via "Sleeping" Volcanoes Can Wake Up Faster Than Thought | National Geographic.

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