Coastal Landscape Evolution in Response to Rapid Base-level Fall at a Hypersaline Lake: a Case Study of Ghor al-Haditha, Dead Sea, Jordan

The ongoing rapid recession of the Dead Sea provides a unique opportunity to examine geomorphological changes related to base level fall along the coast of a hypersaline lake. In this study, we combine high resolution aerial and satellite remote sensing data (≤ 1 m GSD) with digital surface models and orthophoto mosaics (≤ 0.1 m GSD) from several close-range photogrammetric surveys to document the geomorphological development of the area of Ghor Haditha, Jordan, over the 50-year period of base-level decline from 1967 to 2017. Our analysis shows that the base level fall of 35 m in total (currently 1m/yr) has exposed the former lake bed by shore line retreat of up to 2 km at rates and extents dependent on the pre-existing bathymetry. Sinuous or straight/braided stream channels have been carved into the newly-exposed former lake bed due to groundwater seepage or flash flooding, respectively. In addition, more than 1000 sinkholes of metres to several tens of metres in diameter, as well several larger-scale depressions of several hundred metres in diameter, have developed through ground subsidence or collapse. In detail, 3D channel and depression morphologies are linked to the mechanical properties of the alluvial and lacustrine deposits exposed at surface. These subsidence features represent a significant hazard to local infrastructure and agriculture, and probably relate to karstification and/or physical erosion of underlying salt-rich sediments. Shoreline retreat is proposed to drive karstification by enabling the ingress of under-saturated groundwater into lacustrine deposits previously in equilibrium with saturated Dead Sea brine. This is supported by our observation of a general seaward migration of sinkhole development with time.