EXAMPLE OF A CONTINENTAL SABKHA OF THE MIDDLE EAST

Interior continental sabkhas are equilibrium deflation-sedimentation surfaces or "deflation- sedimentation windows" through to the local water table. The capillary fringe above the water table marks the base level of wind deflation. Sediment above this capillary fringe is removed by the wind, hence a flat surface is formed that is related to the groundwater table.

An example of a continental sabkha is the Yotvata Sabkha in the southern Arava Valley between the Dead Sea and the Red Sea. Intermittent streams within the valley flow southward toward the Red Sea, but most of them do not reach it. The intermittent streams are short and do not form a continuous drainage basin. Fans prevent the sediment from reaching the Red Sea; hence the water seeps into the soil, where it forms a water table close to the surface. The sabkha occurs between two dune fields, an extensive to the north and a narrow one to the south. In places, dunes have encroached over part of the sabkha. The sediments of the sabkha consist of sand, silt, and clay brought in by the intermittent streams from the slopes of the graben and by the wind from the north. The sabkha surface slopes away from the walls of the graben and is nearly horizontal in the center of the valley. Depth to groundwater, composition of groundwater, and distribution of vegetation form the basis for distinguishing three zones of sabkha: (1) a central zone barren of vegetation, (2) a transitional zone, and (3) an outer zone with sparse vegetation (includes tamarisks, rushes, and palms). Traced from outer to central zone, the groundwater table rises towards the floor of the sabkha and chlorinity in this direction increases. Gypsum precipitates within the framework of sedimentary particles in the outer and part of the transitional zone; halite precipitates in part of the transitional and in the central zone. Interdune areas in deserts also are commonly deflated to groundwater level, hence form sabkhas.