The present study documents coastal processes of movement and subsidence that affect the clayey sediments of the exposed mudflats ('mudflat sediments') on the receding western shore of the Deep Dead Sea ('western Dead Sea shore') and the formation of subsidence features: subsidence strips and clustered sinkholes. The properties of the clayey sediments that promote movement and subsidence and the development of the subsidence features in the exposed mudflats are the unconsolidated fine-particle texture composed of clay and carbonate minerals, their being dry near the surface and wet at the subsurface, their soaking with saline water and brine and the abundance of smectitic clays saturated with sodium and magnesium. Field observations indicate that narrow subsidence strips with/without clustered sinkholes were developed by movement and subsidence in mudflat sediments via lateral spreading. Wide subsidence strips with clustered sinkholes were developed via increased subsidence in mudflat sediments due to the progress of dissolution within a subsurface rock-salt unit. The emergence of sinkholes occurs via subsidence of mudflat sediments into subsurface cavities resulting from dissolution within a subsidence rock-salt unit. The coastal processes on the receding Dead Sea shore and the formation of the subsidence features are part of the adjustment of the Dead Sea periphery to the lowering of the base level. A contribution of slow mass movement seaward to the coastal processes on the receding Dead Sea shore is indicated.

Mudflat sediments can pose dual challenges of engineering diseases and pollution risks due to unfavourable mechanical performances and potential heavy metal enrichment, impacting coastal engineering construction, ecological environments, and human health. Commonly used Portland cement has significant restrictions in ensuring mechanical stability and environmental sustainability during the remediation of heavy metalcontaminated mudflats. This study investigates a novel approach using chitosan-enhance alkali-activated geopolymer (CS-AGP), composed of slag, fly ash, and desulphurised gypsum, for solidifying/stabilizing highly toxic and concentrated Cu-/Cr(VI)-polluted sediments. The unconfined compressive strength, durability, and leaching toxicity of these sediments are assessed across varying binder incorporations, contamination concentrations, curing periods, and dry-wet cycles. The results demonstrate that the CS-AGP remarkedly increases both early and long-term strength as well as environmental stability of Cu-/Cr(VI)-polluted sediments, even after suffering serious dry-wet alternations and pollutant accumulation, far surpassing the USEPA strength criterion (0.35 MPa) for safe landfill and suiting for in-situ engineering applications. Moreover, the CS-AGP solidified/stabilized contaminated sediments exhibit excellent acid resistance and minimal environmental risk and leaching concentrations meet Cu <= 1.5 mg/L and Cr(VI) <= 0.1 mg/L, as these metals primarily redistribute to the residual fraction. Microstructure evolution reveals CS-AGP generates significant amounts of calcium silicate hydrate, calcium aluminium silicate hydrate, and ettringite to compact sediment skeleton structures, which is the improvement source of mechanical performance. Simultaneously, the comprehensive physical encapsulation, chemical bonding, and coordination effects promote the transformation of Cu/Cr(VI) into a low availability state. The study offers new insights for efficient remediation and safe development of coastal mudflats.