CHEMISTRY AND MINERALOGY OF 4 DUST STORMS IN THE NORTHERN NEGEV DESERT, ISRAEL (1988-1992)

In the Negev desert of Israel, extreme situations of dust storms occuring with airborne dust concentrations (C) above 3000 mug/m3 are generally associated with migrating synoptic systems and with wind directions which prevail from the westerly quadrant. Wind speeds during these extreme situations are high (over 15 m/s), and relative humidity is low (30-40%). In four major dust storms, airborne dust concentration at the Sede Boqer monitoring station in the northern Negev desert reached values higher than 1500 mug/m3 (February 1992); 3000 mug/m3 (May 1988) and 4000 mug/m3 (February 1988 and November 1991), carrying 6-10 tons of pulverized material over an area of at least 200 km2. During these dust storms, the major mineral constituents of airborne dust are quartz and calcite, the minor constituents are gypsum and halite and traces of plagioclase, kaolinite and illite. Many individual dust grains are aggregates of even finer particles. The major elemental constituents were Si and Ca; the minor constituents are Al, Mg and Fe and occasionally Na and Cl; the trace elements are Mn, Ti, K, S and P. The storm wind blew over more than 100 km of alluvium and dunes, chalk, limestone, marl, clay and chert. The relative abundance of Si and Ca is characteristic of the nature of the storm.