THERMAL ANOMALIES ASSOCIATED WITH FORCED AND FREE GROUNDWATER CONVECTION IN THE DEAD-SEA RIFT-VALLEY

The Dead Sea rift valley is a left-lateral transform, along which seve ral rhomb-shaped grabens were formed, At the Sea of Galilee, which is one of these rhomb-shaped grabens, ambiguous heat fluxes were measured : 70-80 mW/m(2) at the central part of the lake, 36 mW/m(2) at the lak e's southern coast (10 km apart), and most surprising, about 135 mW/m( 2) at the southern Golan Heights, 6-8 km east of the graben margin, A detailed geologic cross section, traversing the entire sedimentary bas in, was constructed. The hydrodynamics in this cross section were anal yzed quantitatively using a two-dimensional finite element code that s olves the coupled variable-density ground-water flow and conductive-co nvective heat transfer equations, On the basis of numerical simulation s, different mechanisms of basin-scale groundwater convection are sugg ested for the two sides of the rift that could influence the transport of heat: (1) forced convection (gravity-driven flow) of hot brines fr om deeper aquifers to the land surface at the western side; and (2) la rge scale free convection (buoyancy-driven flow) of deep ground water at the eastern side. The different heat fluxes within the rift valley are attributed to the different lithologies and to the locations of sp ecific conduits through which the hot ground waters ascend from deeper horizons, These simulations also explain the different salinities of the hot springs on the two sides of the rift.