Gravity current

From Glossary of Meteorology

gravity current

A flow driven by horizontal pressure gradients, due typically to the flow of a fluid of one density intruding into an ambient fluid of different density.

In nonrotating fluid, the head of the current travels with uniform horizontal speed
in which g′ is the reduced gravity, H is the current depth, and C is a constant of order unity. Sea breezes, landslides, and some instances of cold water formation are common manifestations of gravity currents in geophysical circumstances.