LARGE-VOLUME VOLCANIC EDIFI CE FAILURES IN CENTRAL AMERICA AND ASSOCIATED HAZARDS

Abstract

Edifi ce-collapse phenomena have, to date, received relatively little attention in Central America, although ̃40 major collapse events (ε0.1 km3) from about two dozen volcanoes are known or inferred in this volcanic arc. Volcanoes subjected to gravitational failure are concentrated at the arc's western and eastern ends. Failures correlate positively with volcano elevation, substrate elevation, edifi ce height, volcano volume, and crustal thickness and inversely with slab descent angle. Collapse orientations are strongly infl uenced by the direction of slope of the underlying basement, and hence are predominately perpendicular to the arc (preferentially to the south) at its extremities and display more variable failure directions in the center of the arc. The frequency of collapse events in Central America is poorly constrained because of the lack of precise dating of deposits, but a collapse interval of ̃1000-2000 yr has been estimated during the Holocene. These high-impact events fortunately occur at low frequency, but the proximity of many Central American volcanoes to highly populated regions, including some of the region's largest cities, requires evaluation of their hazards. The primary risks are from extremely mobile debris avalanches and associated lahars, which in Central America have impacted now-populated areas up to ̃50 km from a source volcano. Lower probability risks associated with volcanic edifi ce collapse derive from laterally directed explosions and tsunamis. The principal hazards of the latter here result from potential impact of debris avalanches into natural or man-made lakes. Much work remains on identifying and describing debris-avalanche deposits in Central America. The identifi cation of potential collapse sites and assessing and monitoring the stability of intact volcanoes is a major challenge for the next decade. © 2006 Geological Society of America.