Geology

A Sleeping Giant

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Science  18 May 2001:
Vol. 292, Issue 5520, pp. 1265
DOI: 10.1126/science.292.5520.1265a

One of Earth's largest recent volcanic eruptions occurred at Toba, Indonesia, about 74,000 years ago. This eruption released an estimated 2800 cubic kilometers of magma and formed a large caldera extending 30 by 100 kilometers; the eruption is thought to have had dramatic effects on Earth's climate.

What might Earth's largest volcano be doing today? Masturyono et al. have conducted a geophysical survey across Toba to image its internal structure, and they identify areas where magma is present down to mantle depths. These data reveal that the caldera contains two separate shallow magma bodies, which can be traced upward to small volcanoes that erupted sometime after the main Toba eruption. The larger of the magma bodies, which makes up about one half of the caldera, narrows at depth but can be traced downward to the mantle. It seems likely that melts in the mantle are providing the heat for crustal melting that forms large explosive reservoirs. — BH

Geochem. Geophys. Geosys.2, 2000GC000096 (2001).

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