Groundwater free thermal convection

The free thermal convection of groundwater, as described here, is attributable to temperature-induced density differences of the groundwater only if it is assumed that there are no other driving forces for groundwater flow. This assumption is unlikely to be met in sedimentary basins. According to Bethke (1989) there has been little work to determine the extent to which free convection persists in the presence of other groundwater flow systems. 

Flow of groundwater driven by osmosis and free thermal and thermohaline convection may occur locally in sedimentary basins. Thermal convection of groundwater can be expected to develop in sedimentary basins with high heat flows or around magmatic intrusions and salt diapirs. Free thermohaline convection may be induced near evaporites. The possible role of osmosis and associated flow of groundwater in sedimentary basins is disputed. 

The increasing temperatures with depth in a sedimentary basin cause a thermal expansion and hence a decrease in density of the groundwater with depth. This vertical density stratification may induce free convection of the groundwater if the critical Rayleigh number (R = 40) is exceeded (e.g. Wood and Hewett, 1982). 

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