Short communication: Runout of rock avalanches limited by basal friction but controlled by fragmentation

Abstract. Rock avalanches produce exceptionally long run-outs that correlate with their rock volume. This relationship has been attributed to the size-dependent dynamic lowering of effective basal friction. However, it also observed similar volumes can span several orders magnitude, suggesting additional controlling factors. Here, we analyse analogue models avalanches, experiments designed test role fragmentation. We show for a fixed low friction, run-out experimental varies over 2 magnitude and is determined by degree fragmentation, while friction acts only as an upper limit on run-out. interpret run-out's dependence fragmentation being controlled competition between mobility enhancing spreading energy-consuming limited formalize this into scaling law based energy conservation, which shows variation in contribute large seen nature.