A satellite perspective on jokulhlaups in Greenland

Methods by remote sensing techniques were developed to locate potential jokulhlaup lakes and to assess the volume of water discharged. To locate potential jokulhlaup lakes, a time sequence of LandSat satellite imagery covering the area was investigated with spectral mapping techniques. The investigations showed how LandSat images can be used to map surface water, glacial ice, and surface temporal anomalies, and when combined with geographic information system (GIS) analysis, potential jokulhlaup lakes could be identified. For assessing the volume of the water discharged, the bottom topography for the jokulhlaup lakes were mapped from stereo images acquired by the ASTER satellite sensor and thereby defining the relations between the lake surface areas and the volumes of water stored in the lakes. Annual lake areas outlined from LandSat images were combined with the area-volume relations to describe the change over time in the volume of water in the lakes and thereby the volume released during jokulhlaups. The results of the volume assessments were validated against recordings from a hydrological station in the downstream lake. The validation underpinned the credibility of the method and as it relies on satellite data that are readily available, the method is applicable for use in many areas of the world.