University of Cambridge
Cambridge, England
Gravity currents are produced by forces between two fluid of different density. These fluids may be gases or liquids of fluidised particulates, and the currents may be along horizontal surfaces or down slopes. The density differences may be due to changes in composition, temperature or concentration of solute or suspended materials. The distance of travel may be small, or it may be large enough for the current to be affected by the earth's rotation In this paper, examples of gravity currents in various situations in the environment are discussed. In the atmosphere, examples being thunderstorm outflows, sea-breeze fronts and escapes of dense gases In the ocean, gravity currents occur, and have been studied at the saline interfaces in estuaries. In the earth sciences, avalanches of snow or other material are important examples. Volcanoes produce viscous gravity currents of basaltic lava and avalanches of pyroclastic flows. Some recent problems in the understanding of gravity currents are discussed and the importance of laboratory experimental work is stressed.