Controls on the formation and sudden drainage of glacier-impounded lakes: implications for jokulhlaup characteristics

Over the past few years there has been an increase in understanding of glacier-impounded or 'ice-dammed' lake behaviour. The spectacular jokulhlaup (catastrophic flood) from Grimsvotn, Iceland in November 1996 has both raised the profile of such events and emphasized the need for awareness of the processes involved. This review summarizes the extent of current knowledge of ice-dammed lakes, highlighting key developments and outlining areas of study still subject to difficulties. Controls on ice-dammed lake formation and persistence are identified, and cycles of jokulhlaup activity are related to glacier fluctuations. Ice-dammed lake drainage trigger mechanisms are reviewed and recent progress in the understanding of such mechanisms is emphasized. Controls on jokulhlaup routing and the development and character of jokulhlaup conduits are discussed and recent advances in jokulhlaup prediction, hydrograph modelling and peak discharge estimation are assessed. A process-based schematic model, drawing on published research, links ice-dammed lake occurrence and drainage to jokulhlaup characteristics. It is demonstrated that ice-dammed lake and ice-dam characteristics ultimately control seven key jokulhlaup attributes which determine the potential impact of jokulhlaups on both landscape and human activity in glaciated regions.