From mixed to hybrid facies volcanic debris avalanche at Colima Volcano: sedimentology and numerical modeling as evidence of transport and emplacement mechanisms

Numerous partial collapses of Colima Volcano have occurred in its history, accompanied by the emplacement of vol- canic debris avalanche deposits (VDADs). The collapse that gener- ated the Tonila VDAD (T-VDAD; ~ 1 km3; ~ 15Ka cal. BP) occurred during“wet”paleoclimaticconditionsinahighhumidityenviron- ment, and water within the volcanic edifice, which played a sig- nificant role in the volcano’s instability and avalanche transport. This study aims to provide new data on the processes involved in the transport and emplacement mechanisms of debris avalanches based on a detailed granulometric and microtextural characteriza- tion and numerical modeling. In general, T-VDAD exhibited mas- sive dynamic behavior during its transport, without segregation process, although some variation of the grains-size occurs from proximal to distal reaches from the source. At microscopic level, evidence suggests particle–particle interactions of rapid, high- energy, high velocity collisional nature, promoting comminution, which increases the fines content with distance. The general high content of fine material into the T-VDAD, combined with a signifi- cant water content within the mass before the collapse, due to par- tial edifice saturation, may have contributed to enhance its mobility. The T-VDAD mobility is here tested with the Titan2d numerical model; results show important paleo-topography implications and that the Coulomb frictional model with basal friction angles simi- lar to previously tested cases best fits the areal propagation of the T-VDAD, confirming that, despite the fluid content that enhanced downslope transformation, the flow still behaved as a homogeneous and incompressible continuum with energy dissipation concen- trated within its base.