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 glac ier-impounded or 'ice-dammed' lake behaviour. The spectacular jokulhlaup (c atastrophic flood) from Grimsvotn, Iceland in November 1996 has both raised the profile of such events and emphasized the need for awareness of the pr ocesses involved. This review summarizes the extent of current knowledge of ice-dammed lakes, highlighting key developments and outlining areas of stu dy 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 re viewed and recent progress in the understanding of such mechanisms is empha sized. Controls on jokulhlaup routing and the development and character of jokulhlaup conduits are discussed and recent advances in jokulhlaup predict ion, hydrograph modelling and peak discharge estimation are assessed. A pro cess-based schematic model, drawing on published research, links ice-dammed lake occurrence and drainage to jokulhlaup characteristics. It is demonstr ated that ice-dammed lake and ice-dam characteristics ultimately control se ven key jokulhlaup attributes which determine the potential impact of jokul hlaups on both landscape and human activity in glaciated regions.