WIND POWER - THE NEGLECTED GEOLOGICAL FORCE

Geologists and geomorphologists assume that stabilized sand sea can reactivate as a result of severe drought. Although many conceptual models of activation of stabilized dunes are discussed in the literature, none of them give numerical data of reduction in vegetation cover in connection to drought intensity and duration. In our work in the Negev Desert we concluded that after a prolonged drought that brings the annual average rainfall to 60-50 mm, the vegetation cover will be close to zero and the stabilized dunes can reactivate as long as the sand dunes are not covered by bio-crust.

Another important limit for vegetation on sand dunes is wind power, which varies with the cube of wind velocity. Wind power is one of the most important climatic factor determining the formation and activation of sand dunes. Our hysteresis model explains bistability of active and stabilized dunes under the same climate conditions with sufficient amount of rainfall to support vegetation cover that stabilizes the dunes. Hence, activity prevails when the rainfall is too low to support shrubs or grass on the dunes or when the wind erosion is too high to allow germination of shrubs or grass.

The above models can explain the stabilized and active sand seas in the world deserts. Sand seas were active, according to the luminescence dating of sand dunes, during the Pleistocene. We will discuss the existence of coastal active sand dunes in some humid areas based on the very high wind power (DP) and their young age.