The modern wave-induced coastal staircase morphology along the western shores of the Dead Sea

Abstract

This research provides insights into the formation of the coastal cliffs comprising the staircase morphology along the western coast of the Dead Sea as a result of its anthropogenic, regressive modern (last ~50 years) lake-level fall. The analysis of this morphology is based on observations and measurements of the impact of seasonal lake-level rises of 0–0.2 m and 0.7–2 m in normal versus exceptionally wet winters, respectively. We conducted repeated detailed topographic surveys of the shores for characterizing the evolving morphology with time, and coupled them with wind speed and wave amplitude during cliff formations. The detailed lake-level curve and the almost monotonic level decline allow associating each cliff with the exact year and season of its formation. This detailed chronology allowed, in turn, to identify and associate the pronounced and well-documented seasonality in the lake-level fall with the wind and wave data during specific seasons, years, and multi-year episodes. As a result, we can point at the controlling processes and environmental conditions for cliff formation. Under the regional Mediterranean climate with its distinct seasonality, winters are characterized by eastern Mediterranean low-pressure systems, generating the Jordan River flow in its northern headwaters and its discharge into the lake; this discharge controls the level fluctuations. At the Dead Sea area, these winter systems precipitate little. However, they generate high winds and storm waves that erode an additional coastal cliff at the base of the preexisting staircase every winter. Therefore, at the seasonal scale, a clear separation exists between (a) individual, cliff-forming, stronger wind storms operating only during winters under relatively stable water levels, and (b) the ~1-m annual lake-level fall, mostly during summers. This pronounced seasonality in both the wind and lake level (a) dictates the seasonal pace of cliff formation at vertical intervals similar to the magnitude (~1 m) of the annual lake-level fall by evaporation and artificial brine diversion, and (b) facilitates the cliff separation in the landscape. This regular pacing by winter storms, the minor lake-level rises, and the annual evaporation and diversion support the preservation of the individual cliffs that assemble into the staircase morphology in the coarse-clastic delta fronts and mudflats characterizing the recently emerging coast. Anomalous lake-level rises during exceptionally wet winters are more erosive, even with regular wind storms; they create the largest lateral erosion. Under the emerging shore topography, which results from the steep bathymetry, the outcome is cliffs often much higher than the respective amplitude of their causative lake-level rises. This depends on the duration of the rise and of individual storms and indicates that under the variance of the modern hydroclimatology, the abnormal seasonal lake-level rises operating with regular winter storms, can aggressively erode the shore.Proposed plans to stabilize or raise the falling water level of the Dead Sea would induce coastal erosion and stream incision, which would threaten the existing highway and other infrastructure built close to its shore.