Abstract

New, high-quality bathymetric data for Henderson Seamount (about 80 km west of the southern tip of Baja California) reveal complexities of structure that allow comparison with subaerial volcanoes. Henderson is 3.3 km high, with a basal diameter of 33 km, resembling a subaerial shield volcano in gross morphology. The summit is composed of alkali basalts. There is no summit caldera, but a large subcircular depression on the volcano's eastern flank may reflect a trapdoor caldera similar to those of the Canary Island volcanoes, or it may be a large landslide scar. Smaller cones around the base of the central volcano appear to be formed by two different processes, perhaps related to different rates of basaltic extrusion. One cone appears to be topped by a large crater. Morphologically, this structure resembles subaerial cinder cones; thus, its existence suggests that explosive volcanism of the type that forms cinder cones subaerially may occur at abyssal depths.

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