Recent High-Arctic glacial sediment redistribution : a process perspective using airborne lidar
Progressive glacier thinning, retreat and mass loss in the High-Arctic is increasingly exposing forefield sediments to processes of mobilisation and redistribution. In this paper, we quantify forefield sediment redistribution at Midtre Lovénbreen, Svalbard, using repeat light detection and ranging (lidar) surveys conducted in 2003 and 2005 in combination with field-based observations. Average surface lowering of the forefield over the observation period identified from lidar surveys is −0.05 ma−1; and two primary areas of sediment reworking are identified: active fluvial incision of proglacial streams by ~ 2 m and lateral moraine downwasting of similar magnitude. Multivariate analysis of fluvial and climatological field data indicates that observed forefield sediment mobilisation is driven primarily by discharge forcing, but with contributions from thermoerosive processes and stochastic, autogenic sediment supply. During the period of observation, disparity between sediment loss in forefield fluvial systems as calculated from lidar data (3000–4000 × 103 kg) and monitoring of fluvial sediment load (1600–3500 × 103 kg) suggests the likely presence of significant quantities of buried ice beneath a thick debris mantle, as evidenced by field observations. Relatively uniform lowering of the moraine crest identified from our repeat lidar surveys indicates thermoerosion of an ice core. However, simple debris layer thickness modelling indicates an increase in variation of debris layer thickness at lower elevations, providing support for the assertion that moraine disintegration is driven by complex combinations of both thermal and mechanical processes. This study demonstrates the viability of using lidar in conjunction with field monitoring to better understand sedimentary deglaciation dynamics and processes, and also highlights the significance of forefield areas in controlling the sediment yield from deglaciating catchments.