Erosion and morphology of a debris flow caused by a glacial lake outburst flood, Western Norway

This article documents a 240,000-m(3) debris flow resulting from a glacial lake outburst flood in Fjaerland, Western Norway, May 8, 2004. The event started when a glacial lake breached a moraine ridge. The ensuing debris flow was able to erode material along its path, increasing in volume from about 25,000 to 240,000 m(3) before depositing about 3 km from its starting point. Field investigations, pre- and post-flow aerial photographs as well as airborne laser scanning (LIDAR) were used to describe and investigate the flow. The most striking and unusual feature of this case study is the very pronounced erosion and bulking. We have made a detailed study of this aspect. Erosion and entrainment is quantified and the final volume of the debris flow is determined. We also present geometrical and sedimentological features of the final deposit. Based on the Fjaerland data, we suggest that a self-sustaining mechanism might partly explain the extreme growth of debris flows traversing soft terrain.