Remote sounding of Greenland supraglacial melt lakes: Implications for subglacial hydraulics

A supraglacial lake-depth retrieval function is developed, based on the correspondence between moderate-resolution imaging spectroradiometer (MODIS) reflectance and water depth measured during raft surveys. Individual lake depth, area and volume statistics, including short-term temporal changes for Greenland's southwestern ablation region, were compiled for 2000-05. The maximum area of an individual lake was found to be 8.9 km², the maximum volume 53.0 × 10⁶ m³ and the maximum depth 12.2 m, sampling over 0.0625 km² pixel areas. The total lake volume reaches >1 km³ in this region by July each year. The importance of melt lake reservoirs to Greenland ice-sheet flow may be a feedback between abrupt lake drainage events and ice dynamics. Lake-outburst volumes up to 31.5 × 10⁶ m³ d^-1 are capable of providing sufficient water via moulins to hydraulically pressurize the subglacial environment. Since the overburden pressure at the base of a flooded moulin is greater than that provided by ice, lake-outburst events seem capable of exerting sufficient upward force to lift the ice sheet locally, if water flow in the subglacial environment is constrained laterally. Considering a moulin with a 10 m² cross-sectional area, basal pressurization can be maintained over lake-outburst episodes lasting hours to days.