Glacial lake outburst floods (GLOFs) are highly destructive natural disasters in high-mountain regions, and lateral moraine landslides are one of the primary triggers for such events. In October 2023, a lateralSmoraine landslide at South Lhonak Lake in Sikkim, India, led to a catastrophic GLOF, causing significant loss of life and property downstream. By integrating remote sensing interpretation, SBAS-InSAR, and depth-integrated methods, this study investigates the movement process and hazard assessment of the northern lateral moraine landslide at South Lhonak Lake, providing a scientific basis for early warning of landslide-induced GLOFs. The SLBL method was used to estimate the volume of the first landslide at approximately 14.42 million cubic meters. Numerical simulation results show that the maximum velocity of the first landslide reached about 32.5 m/s, with a maximum deposition thickness of about 80 meters. Post-disaster Sentinel-1A data was used to obtain the lateral moraine deformation, identifying a potential secondary landslide area with a volume similar to that of the first landslide, which is currently in a dynamic equilibrium state. However, this area poses a risk of secondary landslides under the influence of heavy rainfall, earthquakes, and other factors. Numerical simulation results indicate that the maximum velocity of the secondary landslide is lower than that of the first, however, the maximum value of the product of flow depth H and the square of flow velocity v (Hvvmax) at the point where the landslide material enters the lake is comparable to that of the first landslide. Due to the closer proximity of the secondary landslide to the terminal moraine and the greater water depth beneath it, the risk of triggering another GLOF remains significant. Sensitivity analysis of the parameters revealed that the basal friction coefficient and pore water pressure coefficient significantly affected the simulation results.