GLOF in the South Lhonak Lake, India: photogrammetric analysis and estimation

ABSTRACT Understanding glaciers and glacial lake behaviors is crucial for assessing natural disasters; however, quantifying these changes remains challenging due to inaccessibility. Glacier melt and landslides can expand lakes, leading to catastrophic flooding. Accurate flood surge estimations and impact assessments depend on continuous monitoring and detailed analysis of terrain changes, typically using digital elevation models (DEMs) derived before and after glacial lake outburst flood (GLOF) events. Traditional empirical methods lack precision, especially in remote areas. During the recent GLOF at the South Lhonak Lake in India, triggered by landslide debris and water surge, significant downstream damage emphasized the need for precise analysis. This study developed an innovative photogrammetric methodology to create DEMs for pre- and post-GLOF events, offering a detailed understanding of terrain changes. Unlike conventional methods using stereo images from a same sensor, this approach utilized a novel single-image photogrammetry technique with stereo images from multiple satellite sensors. This method estimated that 11.50 million cubic meters (MCM) of debris entered the lake, reducing water volume by 43.21 MCM, with a total surge of 54.71 MCM. The study demonstrates the effectiveness of advanced photogrammetry in achieving accurate volumetric estimates, setting a new standard for assessing and mitigating GLOF impacts.