Volcanic "Fizz" That Triggers Explosive Eruptions Starts Deep

Richard A. Lovett
for National Geographic News
July 12, 2007

The fizzy gases that cause some volcanoes to blow their tops—like champagne bubbles popping a cork—appear to originate deep beneath the surface, a new study suggests.

Scientists have long known that during an eruption, gases fizz out of magma as the molten rock rises to the surface.

But in some types of magma, small bubbles coalesce into larger, gaseous "slugs" that rise upward, causing fiery bursts when they reach the surface.

Such is the case at Italy's Stromboli volcano, a 3,050-foot (925-meter) cone that sits on a small island north of Sicily (Italy map).

The volcano has been continuously active for at least 2,000 years, earning it the nickname "Lighthouse of the Mediterranean."

Every 10 to 20 minutes Stromboli shoots fiery blobs in fountainlike geysers as high as 300 feet (100 meters) above the crater.

These bursts, dubbed strombolian eruptions, are associated with seismic activity not far beneath the crater, so volcanologists had assumed that the slugs formed in that region.

But the new study, to be published in tomorrow's issue of the journal Science, found that the belches actually begin much deeper underground—perhaps as deep as the base of the mountain.

Learning more about Stromboli is important, the scientists said, because the mountain produces much larger explosions several times a year (see a photo of a recent Strombli eruption). These violent blasts pose a major hazard for tourists and scientists observing the peak from a nearby overlook.

"Therefore, improved understanding of the processes controlling the different types of explosions at Stromboli is … a high priority," the team wrote.

Gases From the Deep

Mike Burton of Italy's National Institute of Geophysics and Volcanology led the team that studied the gases emitted from Stromboli's main crater.

Continued on Next Page >>


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