ABSTRACT
Pantin 1979). Particle concentrations in the suspension cloud are usually su®ciently low (0.1%–7% by volume) that particleparticle interactions play a small or negligible role in maintaining the suspension (Bagnold 1954). However, this upper limit is contentious and many authors would put it higher (Lowe 1982). At these concentrations in turbidity currents the extra mass of the suspended particles is small relative to that of water, so the Boussinesq approximation, where density di§erences are considered negligible in inertia terms, is reasonable. In contrast, in powder snow avalanches the density di§erence between the suspended particles and the interstitial air is high and the particles may carry most of the žow’s momentum. Nonetheless, due to the extreme di®culty in estimating particle concentrations in natural žows, there remains considerable uncertainty-and debateconcerning the particle loading in large submarine turbidity currents and the validity of the Boussinesq approximation.
