"Probing the Earth’s Interior with Galápagos Volcanoes"

September 7 
Dennis Geist - Geology

Abstract: The Galapagos Islands are best known for their biota, but they also form one of nature's premier natural laboratories for studying the earth's deep interior. The islands are situated adjacent to a giant spreading crack that forms a boundary between two of the earth's tectonic plates, where a characteristic type of magma is produced from the shallow mantle. In contrast, the magmas that have constructed the Galapagos Islands are thought to be derived from a plume upwelling from the earth's deep mantle, and they have a different characteristic composition. The compositions of the erupted lavas can therefore be used as a tracer, to show extensive mixing between the mantle plume and the upper part of the earth's mantle. Once magma is produced, it ascends builds up beneath the volcanoes, causing their surfaces to bulge. We use precision GPS measurements that are telemetered to the University of Idaho to measure this swelling. Sierra Negra volcano is currently (as of September 1) expanding at 77 cm/y, which we attribute to over 10 million cubic meters of magma pushing up from a depth of only 2 km.