Successive collapses of the El Estribo volcanic complex in the Pátzcuaro Lake, Michoacán, Mexico

Abstract

The El Estribo volcanic complex is located in the north-central part of Michoacán State (Mexico) within the Michoacán–Guanajuato Volcanic Field. It consists of a ~126kr shield volcano crowned by a cinder cone, separated by a paleosol dated at 28,360±170BP. The shield volcano has been cut by the E–W normal Pátzcuaro fault that exposes 200-m of piled up lavas flows. Our field reconstruction suggests that two collapses have been originated from this fault. Two debris avalanche deposits with hummocky topography are exposed between this fault and the southern shore of the Pátzcuaro Lake. The basal debris avalanche deposit (BDAD) covers lacustrine sediments and is covered by a paleosol that at 28,110±720yrBP yielding a minimum age for the event. It had a maximum run out of 3.2km with a H/L of 0.0062. The upper debris avalanche deposit (UDAD) is overlain by a paleosol dated at 14,110±60yrBP that yields a minimum age of the event. It had a maximum run out of 2.3km with a H/L of 0.0086. No pyroclastic deposits have been found in association with these debris avalanches and the shield volcano rocks show signs of intense hydrothermal alteration or abundant clay minerals for which we assume that failure was triggered by seismic–tectonic activity.The older debris avalanche was more mobile because it moved on water and on top of water-saturated sediments deforming them and likely originating a tsunami across the lake. Instead, the younger debris avalanche moved across the previous rugged hummocky topography of the basal avalanche resulting in a more restricted dispersion.These collapse events of El Estribo, the morphology of the scarp and historic and modern seismicity indicate that a future failure represents a serious threat to the surrounding communities of the Pátzcuaro Lake. Consequently, some preventive measurements as seismic and deformation rate monitoring are necessary. Today five villages with circa 1500 inhabitants live upon the mass waste deposits.