Shifting slope faces shaky situation.

Shifting slope faces shaky situation

Ground motion near Mount Etna's Valle del Bove caldera has destabilized the caldera's western rim, report geologists who monitor movements of the Sicilian volcano. Further shifts in the caldera--a depression created centuries ago by a collapse in the mountain's eastern slope -- could lead to rockslides, mudslides or even a full-scale eruption, warns British geologist William McGuire of the West London Institute. Since 1981, McGuire and his colleagues have been collecting what he calls the first numerical measurements of ground motion at Mount Etna.

Minor eruptions in 1983 and 1985 drove molten rock upward with enough force to create vertical fissures, or dykes, under the caldera's western rim. The dykes shifted a 1-by-0.5-kilometer block of the rim 2.8 meters to the east, the group reports in the Jan. 25 NATURE. After 1985, the area essentially held its ground until last October, when another dyke moved the same block 1 meter farther to the east, triggering two small rockslides.

The researchers check for ground deformations twice a year, using geodetic stations on Mount Etna. Similar but more frequent monitoring of Mount St. Helen's led geologists to predict that volcano's May 1980 eruption, notes Tom Pierson of the U.S. Geological Survey in Vancouver, Wash. Predicting a landslide or eruption at Mount Etna would require daily monitoring--an impossibly ambitious goal under the project's current funding, McGuire says.