SEISMIC IMAGES OF ACTIVE MAGMA SYSTEMS BENEATH THE EAST PACIFIC RISE BETWEEN 17-DEGREES-05' AND 17-DEGREES-35'S

Seismic reflection data from the East Pacific Rise between 17 degrees 05' and 17 degrees 35'5 image a magma lens that varies regularly in depth and width as ridge morphology changes, confirming the notion that axial morphology can be used to infer ridge magmatic state. However, at 17 degrees 26'S, where the ridge is locally shallow and broad, the magma lens is markedly shallower and wider than predicted from regional trends. In this area, submersible dives reveal recent volcanic eruptions. These observations indicate that it is where the width and depth of the magma chamber differ from regional trends, indicating an enhanced magmatic budget, that is diagnostic of current magmatism.