Sinkhole Precursors and Formation Mechanism along the Dead Sea Shorelines, Israel, Analyzed by InSAR, Field Mapping, Water Analysis and Elastic Modeling

Abstract:

The water level of the Dead Sea (Israel and Jordan) has been dropping at an increasing rate since the 1960s, exceeding a meter per year during the last decade. This water-level drop has triggered the formation of sinkholes and land subsidence along the Dead Sea shorelines, resulting in severe economic loss and infrastructural damage. We demonstrate the use of Interferometric Synthetic Aperture Radar (InSAR) measurements from COSMO-SkyMed images, combined with an airborne Light Detection and Ranging (LiDAR) Digital Elevation Model to detect sinkhole-related subsidence. In several locations, precursory subsidence tens to more than a hundred meters wide, at rates between 0.5 and 2 mm/day started a few months to more than a year before an actual collapse of a sinkhole. The sinkholes, a few meters wide and up to 25 m deep, form generally at the perimeter of the subsiding areas. By means of a simplified model representing a distributed closure of a sill-like crack, we estimate the cavity volume occupied by the subsiding sedimentary overburden and explain the spatial relationships between the gradual surface subsidence and the sinkholes. The subsiding areas and successive sinkholes in a specific site migrate laterally, possibly due to progressive dissolution and widening of the underlying cavities. Combining InSAR measurements with sinkhole mapping and chemical and isotopic analyses of groundwater and surface water, we find a new mode of sinkhole formation. The sinkholes initiate by dissolution of a 10-20 m deep and 5-15 m thick halite layer by fresh groundwater. The process continues and accelerates as flash-floods are drained by existing or by newly formed sinkholes, the subsurface salt layer dissolves rapidly, the overlying ground subsides, and salt-saturated water seeps out downstream of the draining sinkholes. The number of sinkholes and the rates and dimensions of subsidence increase significantly during and immediately after the flood events, and decay exponentially thereafter.