Volcanoes Thought Dormant Called Active

Four volcanoes in the Andes--all previously considered dormant--are active and are either bulging or deflating, according to a precision satellite analysis of the volcanic range. Meanwhile, 50 volcanoes classified as potentially dangerous are not moving at all, says an eight-year analysis of 900 volcanoes in the remote central Andes published in last week’s issue of the journal Nature.

One of the bulging volcanoes, Hualca Hualca, is in a heavily populated region of southern Peru. Such deformation is often caused by magma swelling within a volcano--a precursor to eruptions.

The new study, said Caltech geophysicists Matt Pritchard and Mark Simons, proves the worth of monitoring vast volcanic areas using satellite surveys, which are more sensitive and easier to conduct than conventional ground-based surveys.

The authors suggest that the four active volcanoes they detected be monitored for mudflows, landslides and gas emissions that can accompany eruptions.