Momentum transfer and friction in the debris of rock avalanches: Discussion

Abstract

The authors address an old and stubborn problem. Unfortunately, their [2], assumed from previous work by others, leads to incorrect conclusions. The kinetic energy, K, of the slide mass as it enters the runout surface equals 1 / 2 ~ v i , where M is the slide mass and vo is the entry velocity. The work-energy theorem demands that the change in kinetic energy during the runout from K to zero must equal the total work, W, done by the external forces. It can easily be shown that W equals the first moment of volume of the slide deposits with respect to the starting point of runout, times material density, times the constant g(sin 8-p cos 8). Here, 8 is the constant slope angle of the runout surface and p is the friction coefficient. Therefore, defining L as the final displacement of the centre of gravity of the deposits, [ I ] W = M L g ( s i n 0 p c o s 8 ) = K From this