Implications of glacier detachment triggered by a surge event at Dehdal Glacier in the Pamir Mountains, using daily PlanetScope imagery

Abstract. Surge-type behavior and low-angle glacier detachments in small debris-covered mountain glaciers remain insufficiently documented. This study investigates the surge of the Dehdal Glacier in the northwestern Pamirs during 2025–2026, using daily PlanetScope satellite imagery. Multi-epoch uncrewed aerial vehicle (UAV) orthomosaics and digital elevation model (DEM) differencing from 2019 to 2023 reveal significant pre-surge internal mass redistribution, evidenced by surface thickening of the central tongue and surface lowering in both the upper glacier and the distal tongue, suggesting progressive internal destabilization. Demonstrated by PlanetScope imagery, the surge evolved through three distinct phases, which shows that surge initiation occurred internally and subsequently propagated down-glacier toward the terminus, resulting in detachments, accelerated ice flow, and reoccupation of the valley floor. Two low-angle detachments moved ice up to 4.7 km down-valley, depositing an estimated 4–5 × 10⁶ m³ of ice on the valley floor. By January 12, 2026, the glacier had largely stabilized, with the primary glacier tongue covering approximately 1.83 km² and a detached ice mass of about 0.26 km² persisting farther downstream, resulting in a total ice area of roughly 2.09 km². Notably, the recurrence interval of 9–10 years since the previous surge is significantly shorter than the earlier 20–30-year intervals. This shortened interval is unlikely to be due to seismic activity or to complete reservoir regeneration, and it occurred during warmer, drier conditions than the 1981–2010 baseline, which increased by +1.11 °C. These findings provide new insights into glacier flow instabilities in High Mountain Asia and highlight the geomorphic impacts of small glacier dynamics under increasing climatic stress.