Changes in geometry and subglacial drainage of midre Lovénbreen, Svalbard, determined from digital elevation models

Digital elevation models (DEMs) of the bed and surface of the polythermal Midre Lovénbreen, Svalbard, are used to identify changes in glacier geometry between 1977 and 1995. The calculated mean annual mass balance (-0.61 m water equivalent (w.e) a^-1) is more negative than that derived from field measurements (-0.35 m w.e. a^-1), although the error associated with this value (±0.7 m a^-1) suggests that the difference may be accounted for by errors. However, similar discrepancies between DEM-based and field-based measurements of mass balance been reported elsewhere in Svalbard. Although errors may be responsible, patterns of surface elevation change may also be explained in terms of patterns of ablation, accumulation, and dynamics. The theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure, in 1977 and 1995. These reconstructions are compared with the observed positions of proglacial outlet streams. Decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing, which generally leads to more dispersed drainage. Long-term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry, but short-term changes may also occur in response to early season water pressures, controlled by meteorological and hydrological conditions.