Mudflows as a rate process

Abstract

Rate process ideas can be applied to any particulate flow phenomenon in geomorphology. The appropriate guise for mudflows in particular is the Ree-Eyring relaxation theory of generalised viscous flow. Plastic Non-Newtonian flow takes place in soil-water systems between solids concentrations of 0.25 to 0.65 and at activation energies between 12 and 18 k/cal/mol. This latter indicates that the bonding is of Vander Waals forces between clay particles, while the behaviour of the water component is the result of hydrogen bonding at 4 k/cal/mol. Viscosities are calculated for the range of concentrations exhibiting plastic flow and illustrate the reduction in viscosity with increased shear rates down to values associated with free flowing liquids. Catastrophic flow follows upon a positive feed-back process set in motion by the high shear rates consequent upon some initial impetus; earthquakes, landslides, dam bursts etc. Slow mudflows starting from scratch in most cases fail to take off. The change from slow creep to plastic flow follows upon the separation of clay particles and the destruction of strong bonding and covalent bonding, in the presence of abundant water, with a consequent decrease in the viscosity of the order of nine magnitudes.