Huge volumes of partly molten rock have forced their way upward within Sicily's Mount Etna since 1994, according to a new study of earthquakes under the volcano and bulges at its surface. The intrusions could create more frequent and violent eruptions at the volcano, which just calmed down last week after a spectacular 3-month outburst.
Mount Etna, which towers 3350 meters above Sicily's northeast coast, is the tallest active volcano in Europe. Its eruptions are comparatively gentle, and volcanologists believe it poses no threat of a titanic Mount St. Helens-style blast. Still, Etna's ashes wreak havoc with tourism and daily life in the nearby city of Catania and other towns. Lava flows have also destroyed many structures on the mountain's slopes. Scientists have had a poor grasp of the magma reservoirs deep beneath the volcano's summit, limiting their ability to predict Etna's activity.
Now, those hidden structures have been illuminated by detailed seismic records and surveys of ground deformation during the last 8 years. In a study published online by Science on 6 February, a team led by volcanologist Domenico Patanè of the Istituto Nazionale di Geofisica e Vulcanologia in Catania reports the locations and rupture patterns of 647 earthquakes under and near the mountain. The team also analyzed data that revealed changes in slope and altitude along the volcano's flanks.
By combining the two approaches, Patanè and his colleagues conclude that magma has been continuously injected from a depth of 6 to 15 kilometers below sea level into a series of shallower reservoirs. The injection drastically jacked up the pressures within the upper part of Etna's plumbing system. Moreover, Patanè notes, the new magma was gas-rich, creating unusually explosive lava fountains and ash clouds in the summer of 2001 and from October 2002 until last week. "It seems probable that the next eruptions could occur at relatively brief intervals," Patanè says. The volcano's flanks were "intensely fractured" in 2001 and 2002, he adds, opening pathways for future outbursts.
The study provides the most realistic model of Etna's internal dynamics, comments volcanologist Maurizio Bonafede of the University of Bologna, Italy. Both he and seismologist Stephen Malone of the University of Washington, Seattle, note that it's hard to predict how explosive Etna's outbursts will become, although the volcano provides enough warning signs for safety officials to protect Sicily's citizens.