Dome collapse mechanisms and block-and-ash flow emplacement dynamics inferred from deposit and impact mark analysis, Mono Craters, CA

Impact marks on clast faces that resulted from clast-to-clast interactions recorded details of the impacting mechanism. We analyzed ~ 15,000 marks and report for the first time their size, shape, and sorting to infer the flow regime of the BAF during emplacement, to a distance of ~ 2.6 km from the vent. Clast-to-clast interactions occurred over a broad spectrum from purely collisional (normal to clast faces) to purely frictional (clasts shearing in a unidirectional flow), and recorded a transition to a more frictional flow regime in distal reaches as the sliding head of the BAF decelerated and halted. Finally, we briefly differentiate a similar, but previously undescribed older deposit that predates the 1325-1350 A.D. North Mono eruptive episode.