Mount Etna Morphing to More Explosive Volcano, Study Says

Bijal P. Trivedi
for National Geographic Today
August 29, 2001

Mount Etna's recent outbursts may be a sign that the volcano is developing a more explosive personality.

Sicily's Mount Etna is morphing from a "hot-spot" type of volcano, like the quietly oozing and bubbling volcanoes of Hawaii, to an "island-arc" variety represented by the explosive Mount St. Helens and Mount Pinatubo, according to a controversial new study published in the August 30 issue of Nature.

"Such a transition has never been seen before," said Graham Layne, a geochemist at the Woods Hole Oceanographic Institution in Massachusetts, who described the report as "very provocative."

"The most compelling aspect of this study is that the evolution occurred in less than a hundred thousand years," said Layne.

"That's strikingly fast," he added. "Geologists are used to dealing in periods of at least a few million years."

Study of Lava Flows

The evidence of Mount Etna's evolution comes from Pierre Schiano of Université Blaise Pascal in Clermont-Ferrand, France, and his colleagues. Schiano is lead author of the study published in Nature.

Their finding is based on a study of the lava flows spewed from Mount Etna over the last 500,000 years, which is done by analyzing specific crystals inside pieces of lava. Lava generated by early eruptions has a different geochemical "fingerprint" than more recent flows.

Recent eruptions have produced lava characteristic of explosive island-arc volcanoes. The lava has higher quantities of water and sulfur than lava from hot-spot eruptions that occurred about half a million years ago.

Island-arc volcanoes occur at subduction zones, where two oceanic plates collide and one is pushed under the other. The Marianas Trench is an example of a subduction zone caused by a collision of the Pacific and Philippine plates. The Mariana Islands are volcanic products of the magma, or molten rock, released at this subduction zone.

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