Abstract
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 the effective basal friction. However, it has also been observed that run-outs of rock avalanches with similar volumes can span several orders of magnitude, suggesting additional controlling factors. Here, we analyse analogue models of rock avalanches, with the experiments designed to test the role of dynamic fragmentation. We show that for a fixed low basal friction, the run-out of experimental rock avalanches varies over 2 orders of magnitude and is determined by their degree of fragmentation, while the basal friction acts only as an upper limit on run-out. We interpret the run-out's dependence on fragmentation as being controlled by the competition between mobility enhancing spreading and energy-consuming fragmentation limited by basal friction. We formalize this competition into a scaling law based on energy conservation, which shows that the variation in the degree of fragmentation can contribute to the large variation in run-out of rock avalanches seen in nature.
Highlights
With volumes larger than 109 m3 and speeds reported at over 150 km/h (Campbell, 1989) and possibly up to 100 m/s (Legros, 2002), the destructive power of rock avalanches is unprecedented
We show that for a fixed low basal friction, the run-out of experimental rock avalanches varies over 2 orders of magnitude and is determined by their degree of fragmentation, while the basal friction acts only as an upper limit on run-out
We formalize this competition into a scaling law based on energy conservation, which shows that the variation in the degree of fragmentation can contribute to the large variation in run-out of rock avalanches seen in nature
Summary
With volumes larger than 109 m3 and speeds reported at over 150 km/h (Campbell, 1989) and possibly up to 100 m/s (Legros, 2002), the destructive power of rock avalanches is unprecedented They are exceptional hazards produced when very large rockslides disintegrate during transport (Hungr et al, 2013). The travel distance of the deposit front, or runout, is an important measure for hazard assessment (Vaunat and Leroueil, 2002) and is generally found to be more than 10 times longer than the fall height (Hsü, 1975) This suggests low effective basal friction μeff, which is usually attributed to various dynamic weakening processes
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