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The accepted mechanism for the formation of thousands of sinkholes along the coast of the Dead Sea suggests that their primary cause is dissolution of a salt layer by groundwater undersaturated with respect to halite. This is related to the drop in the Dead Sea level, which caused a corresponding drop of the freshwater‐saltwater interface, resulting in fresher groundwater replacing the brines that were in contact with the salt layer. In this study we used physical laboratory experiments to examine the validity of this mechanism by reproducing the full dynamic natural process and to examine the impact of different hydrogeological characteristics on this process. The experimental results show surface subsidence and sinkhole formation. The stratigraphic configurations of the aquifer, together with the mechanical properties of the salt layer, determine the dynamic patterns of the sinkhole formation (instantaneous versus gradual formation). Laboratory experiments were also used to study the potential impact of future stratification in the Dead Sea, if and when the “Red Sea‐Dead Sea Canal” project is carried out, and the Dead Sea level remains stable. The results show that the dissolution rates are slower by 1 order of magnitude in comparison with a nonstratified saltwater body, and therefore, the processes of salt dissolution and sinkhole formation will be relatively restrained under these conditions.

Laboratory experiments were conducted in a vertical, two-dimensional, rectangular flow tank, simulating the response of a phreatic coastal aquifer to a sea tide. Imposed sinusoidal fluctuations of the saltwater level at one side of the flow tank caused three types of fluctuations: (a) hydraulic head throughout the aquifer, (b) saturation degree within the capillary fringe, and (c) salt concentration surrounding the freshwater-saltwater interface (FSI), all recorded by head, saturation, and salinity sensors, respectively. Significant time lags were observed both in the saturation degree within the unsaturated zone and in the salinity within the FSI. All measured values, recorded by the three types of sensors, were simulated and reproduced using a numerical model. The calibrated model was used for mapping the time lags throughout the aquifer. It was found that the time lag of saturation fluctuations within the unsaturated zone increased upward from the groundwater level as the unsaturated hydraulic conductivity decreased. Similarly, the time lag of salinity fluctuations within the FSI increased downward, with distance from the groundwater level. We interpret the low hydraulic conductivity at the capillary zone as the source of attenuation of both saturation and salinity, because both are controlled by the vertical advection of the whole freshwater body. This advection is significantly slower compared to the dynamics of pressure diffusion. The uniqueness of this study is that it provides quantitative data on the attenuation at the capillary zone and its effect on the salinity time lag in coastal aquifer systems.