“Makhteshim”—Unique Arid Land Erosion Cirques in the Negev

Several peculiar erosion cirquesErosion cirque, termed “makhteshim” in Hebrew (sing. “Makhtesh”), occur in the monoclinal ridges of the Syrian Arc Fold Belt (SAFB) in southern Israel and eastern Sinai. The makhteshim are closed valleys (kind of erosion cirquesErosion cirque) surrounded by steep cliffs 200–400 m high, with a single outlet incised in the steep south eastern flanks of some of the largest monoclines. The present study examines the initial conditions, which seem to be required for the development of the makhteshim in the Negev. These are: (1) a stratigraphic sequence of hard carbonate rocks overlying an easily eroded sandstone unit; (2) an asymmetric fold, which was also a prominent topographic ridge; (3) an erosion surface that truncated the hard carbonate rocks of the fold’s crest and exposed the underlying friable sandstone; (4) a deep transverse valley, which incised in the erosion surface and the structural ridge. This valley is the precursor of the present outlet of the Makhtesh. In the Negev, all the above initial conditions already existed in the Early Miocene. However, the final opening stage of each Makhtesh was triggered by the establishment of a deep erosion base level southeast of each anticlinal ridge. For Makhtesh Hatira, such an erosion base level formed locally and for a limited period in the Early Miocene. The opening of the other makhteshim started in the Late Miocene or Early Pliocene triggered by uplift and eastward tilting of the eastern part of the Negev toward the subsiding Dead Sea Rift. A rapid erosion of the inner parts of the truncated anticlines through the eastward-tilted Miocene transverse valleys, established the present morphology of the makhteshim.