Conditions for the ignition of catastrophically erosive turbidity currents

The basic impediment to a clear understanding of eroding and depositing turbidity currents has been the lack of a proper formulation of bed sediment entrainment. This problem is addressed herein: a detailed analysis indicates that the Bagnold criterion is necessary but insufficient for self-sustaining turbidity currents. The analysis reveals two possible equilibrium states, a relatively low-velocity ignitive state, and a high-velocity, dense catastrophic state. A stability analysis indicates that the ignitive state is unstable; flows below it invariably die out, and flows above it "ignite", i.e. accelerate and entrain sediment to the catastrophic state, which is stable. The ignitive state thus defines the criterion for a self-sustaining turbidity current. Estimates of the catastrophic state suggest that it is highly erosive and competent to scour out submarine canyons.