The energetics of an ablating headscarp in permafrost

Abstract

In arctic regions mass movements in thawing permafrost are common. Although different types of landslides have been identified, one type referred to as a "bimodal flow" has caused a significant amount of interest on account of the unusually high rate of mass wasting associated with this type of flow slide. The flow is characterized by a steep headscarp and a low angle mud flow or tongue at the base of the slide.Although more than one activity contributes to the retreat of the headscarp, the most important process is that of ablation. An obvious anomaly exists between the amount of heat required to sustain the high rates of observed ablation and the amount of heat available from net radiation.The components of the energy balance were identified and a field study was undertaken to quantify these terms. Instrumentation included radiometers, wet and dry thermocouples, anemometers, and a lysimeter to measure the latent heat of condensation of evaporation.The results of this study indicate that all the major terms in the energy balance equation combined to form the source of heat responsible for the high rates of observed ablation. Moreover, they provide a rational basis for controlling bimodal flow slides using different insulation materials.