Gravity Currents (Particle Driven Flows)

Geophysical particle-laden gravity flows are driven by the excess weight of the particles over the surrounding water. Depending on conditions, these flows can be in the form of either very dense granular flows or dilute turbidity currents. In the former, the surrounding fluid mostly acts as a dissipative force. Depending on the different time scales from rest state to steady flows, which can be influenced by the initial volume fraction, the particle inertia, among others, the granular avalanches can display many different features. All of these features are however characterised by the dense granular state of the flows. In turbidity currents, the flow is typically turbulent whose wide range of length scales are typically much larger than the size of the particles and the inter-particle spacing. As a result, the dynamics of the suspended particles is critically dependent on the interaction between the particles and the flow dynamics both by the mean flow and the turbulent eddies. The flow dynamics is then controlled by the back effect of fluid-particle interactions through particle inertia, buoyancy, and dissipation. As a result of the interstitial flow dynamics, the runoff length of turbidity currents can be remarkably very long, sometimes of the order of hundreds of kilometers.