Acoustic Fluidization and the Extraordinary Mobility of Sturzstroms

Sturzstroms are a rare category of rock avalanche that travel vast horizontal distances with only a comparatively small vertical drop in height. Their extraordinary mobility appears to be a consequence of sustained fluid-like behavior during motion, which persists even for driving stresses well below those normally associated with granular flows. One mechanism that may explain this temporary increase in the mobility of rock debris is acoustic fluidization; where transient, high-frequency pressure fluctuations, generated during the initial collapse and subsequent flow of a mass of rock debris, may locally relieve overburden stresses in the rock mass and thus reduce the frictional resistance to slip between fragments. In this paper we develop the acoustic fluidization model for the mechanics of sturzstroms, and discuss the conditions under which this process may sustain fluid-like flow of large rock avalanches at low driving stresses.