Seasonal ice velocity of Drang Drung Glacier, in the western Himalaya, using terrestrial time-lapse camera imaging

Seasonal variability in the ice velocities of slow-moving Himalayan glaciers (≤100 m yr⁻¹; >4000 m a.s.l.) is largely unknown, primarily due to the scarcity of high-resolution observations and the substantial uncertainties associated with satellite-based velocity products. In this study, we present high-frequency terrestrial time-lapse camera (TLC) observations of glacier ice motion from Drang Drung Glacier (33.76° N, 76.30° E), spanning October 2023 to April 2025. The glacier terminus is predominantly lake-terminating, with a smaller land-terminating component, enabling a comparative assessment of spatial variations in ice dynamics.

Our results show spatial heterogeneity in surface velocity. Annual mean velocities at the lake-terminating section (35.4 m yr⁻¹) are nearly twice those observed at the adjacent land-terminating segment (19.5 m yr⁻¹). A primary seasonal cycle is evident in both regions, characterised by summer speedup (June–September) followed by autumn slowdown (September–November). These variations correspond closely with increases in air temperature and solar radiation, and are consistent with the meltwater-driven evolution of the subglacial drainage system from inefficient to efficient, channelised configurations. TLC imagery further captures signatures of active subglacial hydrology and its temporal transitions.

A secondary, modest winter speedup (November–January), followed by persistent deceleration until February, suggests that viscous deformation and associated closure of subglacial channels lead to elevated basal water pressures from trapped meltwater. Vertical ice displacement exhibits substantial seasonal variability (−0.9 to −2.0 m month⁻¹) from June to October, with minimal changes outside this period. Sub-weekly analyses reveal coherent patterns of glacier acceleration, contemporaneous increases in lake turbidity, and uplift of the ice front, indicating rapid responses to fluctuations in basal water pressure. TLC-derived velocities show strong agreement with in-situ GNSS measurements but highlight a marked underestimation of glacier motion in ITS_LIVE satellite products for this site.