THE SPREADING OF MISCIBLE, VISCOUS GRAVITY CURRENTS

Experiments on the spread of a viscous gravity current into a lighter, less viscous fluid, with which it is miscible in all proportions, has shown the critically important effect of diffusion at the interface b etween the two fluids. A thin layer of intermediate density is formed that then flows down the interface to generate a precursor current. Th is loss of fluid from the primary current is responsible for a spreadi ng rate that is much less than that of the equivalent immiscible curre nt. It eventually leads to a state in which the pool of viscous fluid reaches an asymptotic radius, and at which the inflow equals the amoun t of fluid diffusing across the interface. A simple model has been gen erated to describe the most important of these effects.