A theoretical model of cooling viscous gravity currents with temperature - dependent viscosity

Gravity current theory has applications to any geophysical phenomena involving the spreading of fluid on a horizontal interface. Many geological gravity currents (e.g., lava flows and mantle plume heads) are composed of cooling fluid with temperature-dependent viscosity. An axisymmetric gravity current theory accounting for these thermo-viscous effects is thus presented and explored here. Unlike isoviscous gravity currents [Huppert, 1982], cooling variable-viscosity currents do not conserve shape and can undergo a somewhat exotic evolution. For large viscosity contrasts between cold and hot fluid, a constant volume, initially hot, domed current collapses rapidly into a fiat plateau with a steep edge. Gravity currents ejected at a constant volume flux from a central conduit also spread with a flattened plateau shape. Continuously fed currents that have a large hot initial volume develop an outwardly propagating interior plateau. Regardless of initial state, continuously-fed, variable-viscosity currents grow primarily by thickening; this contrasts signficantly from isoviscous currents which grow almost entirely by spreading.