Abstract: On September 10, 2023, Hurricane Daniel struck eastern Libya, producing extreme rainfall and catastrophic flooding that caused successive overtopping failures of the Mansour and Bilad dams in the Derna River Basin. Due to the unavailability of real-time monitoring data, the precise failure sequence of these dams and the evolution mechanism driving the resulting disaster chain remain uncertain. In this study, a cascading-failure flood simulation framework for earth-rock dams, which incorporates structural damage to clay cores, was developed for inversion analysis of the two-stage dam failures in Libya. Comparative validation against historical flood marks and residual breach morphology confirmed that the cascading-failure scenario aligned closely with the actual event. A new quantitative index describing the cascading amplification effect was proposed, and the influence of the failure sequence on both the amplification of successive dam-break floods and the resulting hazardous consequences was systematically examined. Results indicated that the water-impoundment effect of the downstream Bilad Dam was the dominant factor driving the cascading amplification, which decreased as the initial failure time of the Bilad Dam increased. In terms of hazardous consequences, while the cascading amplification effect had a limited impact on the overall inundation extent, the severity of downstream impacts increased proportionally with the cascading amplification factor. This case study enhances understanding of the evolution and hazard mechanisms of cascading dam-failure disaster chains and provides technical support for risk assessment, emergency response, and prevention strategies.