Acoustic fluidization and the extraordinary mobility of sturzstroms
Sturzstroms are a rare category of rock avalanche that travel vast horizon- tal distances with only a comparatively small vertical drop in height. Their extraordi- nary mobility appears to be a consequence of sustained fluid-like behavior during mo- tion, which persists even for driving stresses well below those normally associated with granular flows. One mechanism that may explain this temporary increase in the mobil- ity of rock debris is acoustic fluidization; where transient, high-frequency pressure fluc- tuations, generated during the initial collapse and subsequent flow of a mass of rock de- bris, may locally relieve overburden stresses in the rock mass and thus reduce the fric- tional resistance to slip between fragments. In this paper we develop the acoustic flu- idization 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.