Event-scale evolution of an active glacier surge in East Karakoram, India, from dense optical satellite time series

Glacier surging represents one of the most complex and hazardous modes of glacier instability in high mountain regions, yet its short-term dynamical evolution remains poorly constrained due to limited observations during active phases. In the Eastern Karakoram, several glaciers exhibit surge behaviour that is largely decoupled from direct climatic forcing, complicating hazard assessment and interpretation of glacier change signals. Here, we investigate the event-scale evolution of a currently active surging glacier (RGI2000-v7.0-G-14-18432) in East Karakoram, India, using dense optical satellite time series. Our analysis integrates declassified CORONA imagery, historical toposheets, Landsat (1970s–present), Sentinel-2, and high-resolution PlanetScope data, enabling reconstruction of glacier behaviour across both historical and contemporary timescales. High-frequency optical imagery reveals distinct spatio-temporal patterns of surface deformation between 2015 and 2025, including the progressive development of dense transverse crevassing, longitudinal stretching, widening of flow corridors, and down-glacier advection of debris band.These diagnostic surface features enable robust identification of surge onset, propagation, and deceleration based solely on surface expression, without reliance on elevation-change measurements. Analysis of historical optical imagery reveals no clear geomorphic or kinematic signatures typically associated with surge activity, despite more advanced terminus positions observed during the 1970s. This indicates that the current event represents a previously undocumented surge phase within the observational record. The observed surge behaviour highlights the dominance of internally driven glacier dynamics, expressed through rapid and spatially organized surface reconfiguration, rather than a direct or immediate response to regional climatic variability.

To complement satellite-based observations and capture short-term surface changes during ongoing activity, a ground-based timelapse camera installation and UAV survey is planned at the first-of-its-kind benchmark surge glacier in the Indian Himalaya, providing near-continuous visual records of surge evolution. By focusing on event-scale dynamics resolved through dense optical observations, this study demonstrates the value of surface-based monitoring for capturing transient glacier instabilities that are commonly missed by decadal-scale analyses and underscores the importance of surge-type glaciers as a key component of high-mountain geohazard systems under ongoing climate change.