Glacier structure influence on Himalayan ice-front morphology

We investigate the role of glacier structures in controlling ice-front morphology and dynamics of four Himalayan lake-terminating glaciers over a 20-year period. At Imja, Trakarding, Lumdin and Dang Pu glaciers, lake area was mapped between 2000 and 2020 using Landsat 5/7/8 and Sentinel-2 imagery. Discrete glacier flow units were identified, with glacier structures (e.g., open crevasses, transverse structures, longitudinal structures) digitised using the finest resolution panchromatic bands in each year (30, 15, or 10 m). Mapping revealed a distinct pattern of transverse structures towards the terminus of each glacier that influence ice-front position and morphology and are then exploited via iceberg calving events. Our structural analysis also illustrates the role of subsurface conduits in calving events. During subsurface conduit collapse, glacier recession is enhanced, leading to calving along adjacent transverse structures. Furthermore, our analysis shows that ice-front morphology influences the pattern of glacier recession. Ice fronts with distinct ice aprons undergo slower periods of recession than ice fronts with ice cliffs. We conclude that glacier structures are important in determining ice-front morphologies at lake-terminating Himalayan glaciers, and therefore, structural analysis is vital when assessing future ice-front positions and behaviour, as well as rates of glacier recession.