Glacial retreat in the Himalayan region has intensified over recent decades, caused the rapid growth of moraine-dammed lakes, and raised the risk of glacial lake outburst floods (GLOFs). In the Teesta Basin of Sikkim alone, more than 200 km 2 of glacier area vanished between 1990 and 2010, while the catastrophic South Lhonak Lake outburst in October 2023 underscored the urgency of assessing moraine-dam stability in this tectonically fragile setting. This study investigates the Jakthang Glacier (∼5 500 m a.s.l.) in the Changme Khangpu basin, which has lost over 65% of its area since 1962, giving rise to 14 glacial lakes that may merge into a larger, more hazardous water body. Geotechnical analysis of three moraine dams (MD1, MD2, and MD3) reveals that vertical heterogeneity strongly governs seepage behaviour, with permeable upper layers and cohesive lower sections creating instability under rising lake levels. Internal erosion and piping at material boundaries further exacerbate breaching potential. Among the three moraine sediment dams, MD2 exhibits greater resilience due to higher cohesion and reduced displacement, while MD1 shows pronounced susceptibility to hydrological loading, especially under full saturation. Particle-size distribution highlights the well-graded nature of MD3 as favourable for stability, whereas the gap-graded soils of MD1 and MD2 reduce compaction and increase permeability, elevating long-term risk. Critically low factor of safety values (0.3 to 0.5) in fully saturated conditions across all dams point to inherent structural weakness, necessitating engineered drainage and continuous monitoring. Climatic analysis shows a marked decline in subzero temperature days from 221 days to 209 days over the past four decades, indicating accelerated warming in the Jakthang region. This warming trend is likely to hasten permafrost degradation and further undermine moraine-dam integrity, amplifying the future risk of GLOFs. Collectively, these findings underscore the urgent need for site-specific geotechnical modelling, engineered risk mitigation, and long-term climate-informed monitoring strategies to safeguard downstream communities. • Glacial lake outburst hazard assessment in the Sikkim Himalaya. • Geotechnical analysis of moraine dam material. • Moraine dam stability analysis. • Permafrost degradation effect on moraine dam stability. • Future GLOF probability in the Jakthang glacier region.
Misra et al. (Wed,) studied this question.