Rapid lake expansion and sudden outburst events have emerged as critical hydrological phenomena on the Qinghai—Tibet Plateau (QTP), reshaping endorheic basins and threatening downstream ecosystems and communities. However, the mechanisms and impacts of large endorheic lake failures remain poorly understood, as most studies have focused on glacial lake outbursts. The catastrophic outburst of Aksu Kule Lake (AKL) in the Kunlun Mountains in September 2024 provided a rare opportunity to investigate how prolonged hydrological accumulation in endorheic lakes on the QTP under climate change can trigger basin reorganization and flood disasters. In this study, multisource optical remote sensing data were integrated with ICESat and CryoSat-2 satellite altimetry data to systematically assess changes in lake surface area and water level and to examine the underlying mechanisms driving rapid expansion and eventual catastrophic outbursts. The rapid expansion and subsequent outburst of AKL were driven primarily by increased precipitation, especially extreme short-term events in 2010 and 2016. These events contributed approximately 1.5 × 10⁷ m³ and 7.4 × 10⁷ m³ of additional lake water, respectively, accounting for 13.85% and 68.08%, respectively, of the total increase in net volume from 2009 to 2023. The final outburst was initiated by overtopping and subsequent erosion of unconsolidated alluvial fan sediments at the lake outlet, rather than by the structural failure of a natural dam, underscoring the inherent vulnerability of alluvial-dammed lakes. Following the AKL outburst, the Endere River Basin expanded by 81.4%, and the original hydrological regulation capacity of the lake was compromised, potentially resulting in an increased frequency and magnitude of floods in this basin. These findings enhance understanding of rapid lake expansion and outburst mechanisms and provide a scientific basis for early-warning systems and adaptive water management strategies in endorheic basins of the QTP under climate warming.