Heat Flow and the Hydrologic Cycle: Examples from Israel

Abstract

The surface pattern of terrestrial heat flow in Israel is a product of several coexisting mechanisms. Within the sedimentary sequence blanketing over the Precambrian basement of the Arabo-Nubian Massif deep terrestrial heat flow is redistributed, particularly within the depth range of the active hydrologic cycle, by ground water movement. A dense fault network, associated mostly with the Jordan-Dead Sea-Red Sea Rift, facilitates the hydro-logic recharge and discharge system, generating occurrence of numerous hot springs. In the recharge regions, where cool meteoric waters percolate into the subsurface, heat flow values as low as 7.1 mWm−2 were observed. In discharge regions, with abundance of warm to hot ground water ascending along fault structures, heat flow anomalies as high as 464 mWm−2 were recorded. The deep heat flow apparently unaffected by hydrologic cycle was obtained in 23 boreholes, with an average of 52.3 ±17.2 mWm−2. Distribution of the results indicated, however, that only 13 measurements averaging 39.3 ±5.9 mWm−2 represent “normal” regional heat flow, whereas the remaining 10, ranging from 56.9 to 84.6 mWm−2, indicate existence of some mild deep-seated geothermal anomalies of unknown nature. The value of about 40 mWm−2 is consistent with pertinent data on the crustal thickness in the area.