A surge-detachment sequence at Dehdal Glacier in the Pamir Mountains, revealed by daily PlanetScope imagery

Surge-type behaviour and low-angle glacier detachment are distinct but potentially linked forms of dynamic instability that remain insufficiently documented in small debris-covered mountain glaciers. This study investigates the 2025–2026 event at Dehdal Glacier in the northwestern Pamirs, which we interpret as a surge-detachment sequence, using daily PlanetScope imagery. Multi-epoch uncrewed aerial vehicle (UAV) orthomosaics and digital elevation model (DEM) differencing from 2019 to 2023 reveal pre-event mass redistribution, evidenced by surface thickening of the central tongue and surface lowering in both the upper glacier and the distal tongue, indicating pre-surge ice mass redistribution. Daily PlanetScope imagery documents visible surface deformation before the first detachment, renewed advance of the dynamically connected glacier tongue following the first detachment, and widespread acceleration coincident with the second detachment. Together, these observations support a surge–detachment sequence rather than an isolated glacier detachment. Two low-angle detachments displaced ice up to 4.7 km down-valley, depositing an estimated 4–5×10 6 m 3 of ice on the valley floor. By 12 January 2026, the glacier had largely stabilized, with the primary glacier tongue covering approximately 1.83 km 2 and a detached ice mass of about 0.26 km 2 persisting farther downstream, resulting in a total ice area of roughly 2.09 km 2 . Notably, the recurrence interval of 9–10 years since the previous surge is substantially shorter than the earlier intervals of approximately 20–45 years. This shortened interval is unlikely to reflect complete reservoir regeneration, and no clear seismic trigger was identified. The event occurred during warmer, drier conditions than the 1981–2010 baseline, with mean monthly temperature anomalies reaching +1.11 °C. These findings provide new insights into glacier flow instabilities in High Mountain Asia and highlight the geomorphic impacts of surge-related acceleration followed by localized mechanical detachment in small debris-affected mountain glaciers.