Thermal anomalies associated with forced and free ground-water convection in the Dead Sea rift valley

The Dead Sea rift valley is a left-lateral transform, along which several rhombshaped grabens were formed. At the Sea of Galilee, which is one of these rhomb-shaped grabens, ambiguous heat fluxes were measured: 70-80 mW/m² at the central part of the lake, 36 mW/m² at the lake's southern coast (10 km apart), and most surprising, about 135 mW/m² at the southern Golan Heights, 6-8 km east of the graben margin. A detailed geologic cross section, traversing the entire sedimentary basin, was constructed. The hydrodynamics in this cross section were analyzed quantitatively using a two-dimensional finite element code that solves the coupled variable-density ground-water flow and conductive-convective heat transfer equations. On the basis of numerical simulations, different mechanisms of basin-scale groundwater convection are suggested for the two sides of the rift that could influence the transport of heat: (1) forced convection (gravitydriven flow) of hot brines from deeper aquifers to the land surface at the western side; and (2) large-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 Iithologies and to the locations of specific 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.