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July 22, 2010 - To most people, Stromboli is an Italian sandwich filled with meat and cheese but to Jenny Suckale, a MIT grad student, Stromboli is an Italian volcano filled with clues - and magma, of course - for her research.

JENNY is a student in MIT's Department of Earth, Atmospheric and Planetary Sciences, EAPS. She has developed a sophisticated computer model to simulate Stromboli's magma flow, according to a MIT press release. Although scientists have a general idea of how a volcano erupts as liquid magma and gases force their way to Earth's surface, eruptions are difficult to study. But Italy's Stromboli volcano has been erupting every five to 20 minutes for thousands of years so it provides scientists with a living lab for research.

According to the U.S Geological Survey, USGS, Strombolian eruptions are characterized by the Word of the Day

intermittent explosion or fountaining of basaltic lava from a single vent or crater. Each episode is caused by the release of volcanic gases, and they typically occur every few minutes or so, sometimes rhythmically and sometimes irregularly. The lava fragments generally consist of partially molten volcanic bombs that become rounded as they fly through the air.

Map of major volcanoes in Italy (USGS map)

For several decades, scientists have pretty much used one theory to explain what is causing huge amounts of gas to erupt so frequently: swimming-pool-sized bubbles that travel through a few hundred meters of molten magma before popping at the surface, according to a MIT press release.

But Jenny has a different idea. She suggests that giant gas bubbles can't be driving the Stromboli eruptions because such bubbles aren't compatible with the basic laws of fluid dynamics, or the science of how fluids move. Instead of large bubbles that pop at the top of Stromboli's conduits - pipelike openings that connect the volcano's magma chamber to the Earth's surface - Jenny thinks that the eruptions are caused by a spongelike plug located within the conduit, similar to a cork in a champagne bottle, that fractures every few minutes as a result of pressure created by significantly smaller bubbles.

Despite having a wealth of data about Stromboli, volcanologists have really only applied one model to explain Stromboli's continuous eruptions, Jenny says. According to the so-called "big bubble paradigm," as magma rises to Stromboli's surface, pressure drops, and this creates gas bubbles that merge together and can become several meters wide. Eventually, these bubbles explode at the top of the conduit.

But the problem with this theory, according to Jenny, is that it conflicts with the basic principles of fluid dynamics. Specifically, magma doesn't have enough surface tension (created when two fluids meet) or viscosity (a measure of a fluid's resistance) to maintain bubbles larger than a few dozen centimeters. She thinks that many researchers have assumed that bubbles inside Stromboli behave similarly to bubbles in a tank of water. "People take lab models as an analog for the volcano, but the scale is so different, and fluid dynamics is so dependent on scale," she explains.

Jenny still believes there are gas bubbles inside Stromboli that are created by some unknown source located underneath the volcano. But she thinks these bubbles are significantly smaller - perhaps only several centimeters thick - and accumulate beneath a porous plug that covers part of the volcano. As the bubbles exert greater pressure on the plug, it eventually fractures, causing gas, rocks and liquid to scatter into the sky. This could explain why samples of Stromboli rock contain many tiny crystals - because the top of Stromboli is a spongelike plug of crystals and gas bubbles that releases lots of gas every few minutes.

Jenny's work is detailed in a two-paper series published July 20 in The Journal of Geophysical Research.


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