Características microtexturales como indicadores del transporte y emplazamiento de dos depósitos de avalancha de escombros del Volcán de Colima (México)

During its history Colima volcano has experienced numerous partial edifice sector collapses with the emplacement of debris avalanche deposits (DAD) of contrasting volume, morphology and texture. A previous detailed stratigraphic study in the southeastern sector of the volcano described by Roverato et al. (2011, J. Volc. Geoth. Res., 207, 33-46) allowed the recognition of two debris avalanche deposits named San Marcos DAD (SM-DAD V= ~1.3 km3) and Tonila DAD (T-DAD V= ~1 km3). Radiocarbon dates of organic material, directly associated with these deposits, gave ages of >28 kyr cal. BP for the SM-DAD and ~15 kyr cal. BP for the T-DAD. The San Marcos collapse was promoted by ongoing volcanotectonic deformation. The failure event triggered a "dry" debris avalanche (water content <10%). In contrast, the Tonila failure occurred in "wet" paleoclimate conditions during a period characterized by high humidity; the fact that the volcanic system was partially water-saturated was an important factor in the volcanic instability and transportation processes. This work sheds light on the transport and emplacement mechanisms of debris avalanches based on a detailed granulometric and microtextural analysis of the studied deposits. SM-DAD and T-DAD had a massive dynamic behavior during their emplacement, characterized by a lack of selective depositional process. The SM-DAD originated from a "dry" inertial granular flow in which high-energy grain-grain interaction prevailed. Abundant fines and fluids within the mass before the collapse could have enhanced its mobility. In fact, the water content in the flowing mass promoted positive pore-water pressure that reduced the frictional energy dissipation enhancing flow mobility. Both DADs show partially broken crystals/particles, percussion marks and fractures of different intensity that are the result of punctual, rapid and high-energy impacts. In general, the observed microscopic features suggest that the particle-particle interaction occurred in a collisional regime characterized by grains subjected to short, high velocity impacts, while evidence of frictional interaction is less common than that of the collisional type.