Emplacement of volcanic debris landslide deposits: new insight from distinct element numerical simulations

The emplacement processes of large-scale volcanic debris avalanche events remain poorly understood. Much of what we know about this complex process is interpreted from deposits that typically contain a suite of commonly observed characteristics including preservation of original stratigraphy and finer-grained basal (shearing) layers. Interpreting the formation and evolution of these structures is key to understanding the processes that occur after flank/sector detachment has commenced. A distinct element numerical modelling technique has been used to investigate the volcano avalanche emplacement processes. Particle bonding is introduced to a generalized flank collapse scenario; when stresses are overcome in the failed mass, the bond breaks. Material with pervasive bond breakage subsequently behaves as a granular material. This approach allows brittle discontinuities to emerge in the flow as the avalanche propagates through the runout space. Initial results are in good agreement with deposit structures observed in the field and in ASTER satellite imagery. These include the development of hummocky topography, toreva block formation and a progressive rounding of blocks of bonded particles. These blocks are present primarily on the surface of the subsequent deposit and decrease in size distally. Additionally, no particle bonds remain along the basal surface of the simulated deposit, implying the presence of a basal shearing layer, a mechanism believed responsible for long runouts in real world avalanches.