LiDAR-Constrained Multi-Temporal UAV Monitoring of Glacier Terminus Retreat and Secondary Landslide Evolution at Hailuogou Glacier, Mt. Gongga, China

Joint quantification of glacier terminus change and adjacent secondary landslide evolution can be challenging when multi-temporal UAV datasets lack a consistent absolute spatial reference, thereby limiting robust assessment of their stage-dependent covariation. This study investigated the Hailuogou glacier terminus and the Laoguanjingtai (LGJT) landslide using six UAV photogrammetric surveys acquired between 2018 and 2022 and synchronous airborne light detection and ranging (LiDAR) data from 2022. LiDAR reference constraints and elevation-residual assessment over relatively stable terrain supported multi-temporal digital elevation model (DEM) differencing. The glacier terminus area decreased from 2.63×105m2 to 1.43×105m2, representing a reduction of 45.5%. From July 2020 to August 2022, the glacier volume ablation rate reached 1.00×106m3a−1. Meanwhile, the LGJT landslide shifted from deposition-dominated adjustment from 2018 to 2019 to erosion-dominated material export after July 2020, when its erosion rate reached 3.73×105m3a−1 and its net volume change rate decreased to −3.39×105m3a−1. Annualized rates across five unequal intervals showed positive covariation between glacier ablation and landslide erosion and negative covariation with net landslide volume change. These exploratory associations, together with the spatial concentration of elevation change near the glacier–landslide margin, are consistent with a geomorphic linkage. The LiDAR-constrained UAV workflow provides a practical basis for integrated monitoring of glacier retreat and adjacent sediment redistribution.