Remote Sensing Reconstruction and Mechanism Analysis of the July 2025 Glacial Lake Outburst Flood (GLOF) at the Gyirong Port, China-Nepal Border

Glacial retreat in the Himalayas has led to more frequent glacial lake outburst floods (GLOFs), which often pose serious transboundary threats. On July 8, 2025, a GLOF occurred in the Donglin Zangbo Basin near Gyirong Port, triggering a large-scale debris flow across the China-Nepal border. Due to the lack of field data in this remote area, we reconstructed the disaster process using multi-source remote sensing and high-resolution Gaofen-7 (GF-7) terrain data. Our analysis shows the lake expanded rapidly to 0.6  km². By establishing a water level–area–capacity (L-A-V) relationship, the total storage was estimated at 8.0-8.5 × 10⁶ m³, with a released volume of 5.0-6.0 × 10⁶ m³. Based on remote sensing-derived breach morphology, the peak discharge was calculated at 1100-1400 m³, showing high consistency with downstream hydrological records. Notably, a distinct discrepancy between the estimated outburst volume and downstream flood hydrographs suggests complex subglacial hydrological mechanisms, specifically the "bulking effect" caused by intense sediment entrainment and potential englacial drainage. These findings underscore the non-linear amplification of GLOF disaster chains and demonstrate the indispensable value of remote sensing in hazard assessment.