Makhtesh Hatzera Erosion Cirque, the Negev Desert—Landforms and Sediment Dynamics

Quantitative GIS-based analysis of the morpho-stratigraphic map of the Makhtesh Hatzera Erosion Cirque (MHEC) and RTL ages of the eight alluvial terraces (Plakht 2003) were used to calculate the volumes and rates of sediments transported outside the cirque through its opening, specifically during the last > 500 ka and since its initiation in the Pliocene (~5 Ma). The calculated average rates of sediment transport for the entire MHEC are 1840 m3 year−1. For the alluvial terraces, the rates range between 344 and 1328 m3 year−1, which are similar to the present-day rates as documented at a small reservoir in the MHEC. An earlier study showed that floods at the Hatzera stream such as the 2004 flood (470 m3 s−1) can transport boulders up to 2.1 m and weighing up to 15 tons at least once in 120 years. This size is about the maximum boulder size that was found on the terraces within the cirque. Field survey across the terraces shows, as expected, that (a) the desert pavement and soil parameters systematically and gradually change from the active channel and the sub-recent terrace to the oldest terrace due to the increasingly longer intervals of weathering, dust accumulation and pedogenesispedogenesis; (b) the boulder size is reduced up the alluvial terraces sequence—i.e. with time, due to desert weathering and they almost completely disappear within about 100 ka. Sediment evacuation from the erosion cirque as well as the size of the opening are highly controlled by the flood regime which transports the sediments that are directly related to the climatic conditions. Periods of slow sediment aggradation coincide with the build-up of the alluvial terraces and correlate with more humid periods, whereas rapid incision phases characterize more arid conditions.