Preprints
https://doi.org/10.5194/egusphere-2026-4065
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2026-4065
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
12 Aug 2026
| 12 Aug 2026
Status: this preprint is open for discussion and under review for The Cryosphere (TC).
Brief communication: Repeated supraglacial lake drainage from the Purepu Glacier system, central Himalaya
Abstract. We report repeated drainage from the Purepu supraglacial lake system in the central Himalaya using high-resolution satellite imagery. A satellite-inferred 2023 drainage event is constrained to 12–15 July, whereas a reported GLOF occurred early on 8 July 2025. Both followed lake expansion to ~0.70–0.72 km², but DEM-constrained lake-volume loss increased from 0.87 × 10⁶ m³ in 2023 to 3.55 × 10⁶ m³ in 2025. The 2025 event remained incomplete, and flood-volume reconstruction suggests additional englacial or subglacial contributions cannot be excluded. Residual water persisted into 2026, supporting high-frequency monitoring in early July 2026.
How to cite. Xu, Q., Kang, S., Du, W., Wu, W., Hu, Z., He, X., Cao, B., and Xie, B.: Brief communication: Repeated supraglacial lake drainage from the Purepu Glacier system, central Himalaya, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2026-4065, 2026.
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Qiangqiang Xu
State Key Laboratory of Cryospheric Science and Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
Qilian Mountains Field Research Station for Interactions among Cryosphere and Multi-spheres, China Meteorological Administration. Lanzhou 730000, China
Shichang Kang
CORRESPONDING AUTHOR
Key Laboratory of Mountain Hazards and Engineering Resilience, Institute of Mountain Hazard and Environment, Chinese Academy of Sciences, Chengdu 610213, China
Wentao Du
CORRESPONDING AUTHOR
State Key Laboratory of Cryospheric Science and Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
Qilian Mountains Field Research Station for Interactions among Cryosphere and Multi-spheres, China Meteorological Administration. Lanzhou 730000, China
Wei Wu
Department of Disaster Assessment, National Disaster Reduction Centre of China, Ministry of Emergency Management, Beijing 100124, China
Zhaofu Hu
State Key Laboratory of Cryospheric Science and Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
Qilian Mountains Field Research Station for Interactions among Cryosphere and Multi-spheres, China Meteorological Administration. Lanzhou 730000, China
Xiaobo He
Tanggula Mountain Cryosphere and Environment Observation and Research Station of Tibet Autonomous Region, State Key Laboratory of Cryospheric Science and Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
Bo Cao
Key Laboratory of Western China’s Environmental Systems (MOE), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China
Gansu Shiyang River Basin Scientific Observing Station, Lanzhou 730000, China
Biwen Xie
Key Laboratory of Western China’s Environmental Systems (MOE), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China
Short summary
Using frequent high-resolution satellite images, we reconstructed repeated drainage from lakes on the surface of Purepu Glacier in 2023 and 2025. The lakes reached similar sizes before drainage, but the 2025 event released much more water and left substantial residual water into 2026. The results show that lake area alone cannot describe drainage hazard and support intensive monitoring during early to mid-July 2026.
Using frequent high-resolution satellite images, we reconstructed repeated drainage from lakes...
This manuscript documents two drainage events in 2023 and 2025 from the Purepu supraglacial lake system on a debris-covered glacier in the central Himalaya, upstream of the Rasuwagadhi Friendship Bridge and hydropower project. This channel is where the 2026 giant glacier collapse happened. Using primarily PlanetScope high-resolution optical imagery, supplemented by Sentinel-1/2, Landsat 8/9, and an 8 m HMA DEM, the authors reconstruct pre- and post-drainage lake situations, calculate an area-based drainage completeness metric, and derive first-order DEM-constrained drainage water volume. Both events were preceded by similar peak lake extents, yet the 2023 event drained nearly completely while the 2025 event left substantial residual water. The authors analyzed a possible evidence of englacial/subglacial water contribution beyond what is captured by surface lake area change in the drainage event. The paper argues for continued high-frequency, multi-sensor monitoring through the monsoon season given the risk to downstream infrastructure.
Major issues:
The study makes a useful empirical contribution by documenting rare repeated drainage behavior and highlighting monsoon-season monitoring gaps, but its quantitative conclusions about volume loss and hidden water sources would benefit substantially from uncertainty analysis and independent validation before being treated as firm evidence rather than a first-order approximation.
1. The authors used 8m HMA DEM to estimate the drained water volume. However the data does not correspond in time to either drainage event, and no field bathymetry, discharge, or channel-geometry data validate the derived volumes. The authors note their volume estimate for 2025 is roughly half of an independent bathymetric estimate (Zhang et al., 2026). It should be discussed more in detail how the difference of DEM data could influence the results.
2. Some key numbers in the manuscript lack uncertainty quantification. The 16 m shoreline buffer and water-level proxy method were applied uniformly without a sensitivity analysis, so the reported ΔV values lack error bounds. The authors should consider about the uncertainty.
3. The authors attributed the water-budget discrepancies of two events to englacial/subglacial reservoirs. This is reasonable. However, without additional constraints, this remains a plausible hypothesis rather than a demonstrated mechanism, and alternative explanations (e.g., differing DEM resolution or bathymetric assumptions) are not ruled out. It need more discussions in the manuscript.
4. Transboundary Himalayan flows routinely transform into hyperconcentrated or debris flows through channel-bed entrainment. This manuscript lacks of downstream hazard modeling. At least the authors can add discussion on this issue.