Wave transport of deep mantle material

Abstract

Fluid with a certain density and viscosity can rise by buoyant Poiseuille flow through a conduit1 within a second fluid of greater density and viscosity. Such conduits exhibit a rich behaviour characteristic of nonlinear systems, an aspect of which is the formation of solitary waves2,3. Here we present theoretical and experimental studies of these systems. Both approaches reveal that solitary waves trap material in a cell with closed streamlines and that the central streamline velocity is faster than the wave speed. Hence, parcels of deep material are transported directly upward over large distances. This is in contrast to the usual situation in which wave propagation through a medium causes only small displacement of fluid particles. Material in these parcels will be far less contaminated by diffusion from the surroundings than would be material in ordinary pipe flow. In addition, solitary waves are more efficient than buoyant spheres at conveying material upward. We suggest that such waves might exist in the Earth's mantle, conveying uncontaminated deep mantle material to the surface of the Earth.