Geophysics

Infamous Volcanoes

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Science  22 Nov 2002:
Vol. 298, Issue 5598, pp. 1517
DOI: 10.1126/science.298.5598.1517b

Seismic data can now provide detailed views of magma systems in active volcanoes and how these are related to recent eruptions and regional tectonics and volcanic hazards. Several approaches are used, but all rely on the fact that sound waves travel better through solid rock than through liquids (if at all) and that earthquakes can occur near where magma is migrating, but not within a magma body.

Musumeci et al. examined the distribution of microearthquakes in the late 1990s around Mount St. Helens and show that under the volcano is a narrow conduit extending down to about 5.5 km, where the main magma body lies. The magma seems to be injected periodically into a dike-like body controlled by a gap in a regional strike-slip fault. Di Stefano and Chiarabba, using tomography, show that the magma chamber under Vesuvius extends from near sea level to a depth of 2.5 km and likely merges with a larger chamber at a depth of about 10 km. Smaller dikes from this chamber extend toward vents that erupted in the 20th century. — BH

J. Geophys. Res.107, 2264; 2278 (2002).

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