Avalanche Dynamics

Abstract

ABSTRACT. This article reviews recent work on avalanche, landslide and rockfall dynamics. Two limiting cases of these flows exist, the so-called jIow avalanche, i. e., the dense gravity driven "laminar type flow" in which the role of the solid particles dominates, while that of the interstitial fluid is negligible -these flows are typical for most sturzstroms, debris flows, landslides, rockfalls and snow avalanches -and the less dense powder avalanche, i. e., the turbulent flow of air borne particles in a mixture, in which the role of the fluid dominates, while that of the particles is less significantthese flows are typical for density and turbidity currents such as dust clouds occuring in the desert, in pyroclastic volcanic eruptions, in submarine slope instabilities and in snow and ice avalanches. The latter application will be our focus. The state of the art in the description of both these phenomena is given. In the Introduction, after some historical remarks, we turn our attention to the characterization of the physical behaviour of the two limiting flow types and then discuss the laws of similitude and model theory relevant to modelling the flows in the laboratory. Flow avalanches, landslides and rockfalls are discussed first. It is argued that these flows can be described as a continuum consisting of a cohesionless granular material. Such materials exhibit dilatancy effects and large energy dissipation, and under quasistatic or dynamic shear deformation, they exhibit the property that the ratio of the shear stress to the normal stress on any interior plane is nearly constant, a fact reflected in the constancy of the internal angle of friction. In shear cell tests under quasistatic and rapid deformation at constant normal load, the internal stress is practically independent of the rate of shear; when the shear deformation is performed at constant volume however, the dependence of the stress on the rate of shear is quadratic. Three different flow regimes which partly interact can be distinguished: (i), Dry Coulomb, rubbing frictional behaviour, typical when particles are in contact and ride one over the other; (ii), collisional interactions when particles bounce against each other, contact is short, and the mean free path is of the order of the particle diameter; (iii), translational transport when the mean free path is large and particle concentrations correspondingly smalI. For the second and the third regime, statistical theories along the lines of the kinetic theory of a dense gas have been developed, but some of these show ill behaviour in steady chute flow problems. An adequate formulation must incorporate quasistatic and collisional contributions; the emerging theories, however, are patched together from alien components. Furthermore, simple chute flow problems turn out to be very difficult to solve. In the flow regime 317 V. P. Singh (ed.), Hydrology of Disasters

The 26 December (Boxing Day) 1997 sector collapse and debris avalanche at Soufrière Hills Volcano, Montserrat

“…This ratio can be crudely interpreted in terms of the apparent friction coefficient of the avalanche (Pariseau & Voight 1979), and thus the apparent friction angle is around [12][13] o . This result suggests that much of the initial potential energy was consumed by basal friction (Hutter 1996), and that local topography variations did not too strongly influence runout.…”

Dense Granular Avalanches: Mathematical Description and Experimental Validation

“…The details of this analysis have been performed many times and are well documented in the literature, see e.g. [4,5,6,7,8,9,12,13,14,15,17,19,20], the most useful references probably being [6,17]. …”

“…given in [8,9]. A further article on avalanches -mostly from the practical side -is given by Ancey (Chap.…”

Monte Carlo calibration of avalanches described as Coulomb fluid flows

“…the velocity, impact pressure and geometry) of extreme avalanches for various land-use planning and engineering applications, including avalanche zoning and mitigation. Although snow avalanches are complex phenomena involving varied processes from snowfall to snow friction, there is growing evidence that their chief dynamic features can be described by using simple deterministic models (Hutter 1996).…”