Glacier Outburst Floods: A Study of the Processes controlling the Drainage of Glacier-dammed Lakes

 

Glacier outburst floods (jökulhlaups) are caused by the sudden drainage of glacier-dammed lakes. During such an event, the discharge can increase by more than one order of magnitude within a short time period (hours to days). Jökulhlaups pose a significant hazard potential and have caused substantial damage in the past in the Alps and elsewhere. The assessment and prevention of hazards related to jökulhlaups require a reliable prediction of the timing, duration and magnitude of the outburst floods. Despite much progress, several aspects of recent observations were unexpected and highlight the need to improve existing theories. In particular, the rapid rise of discharge during some jökulhlaups indicate that during the start of the drainage different physical processes may be important. The proposed study will address some important open questions of the subglacial drainage process in a combined field and numerical modeling project. In particular, we propose to study the drainage of the Gornersee located at the confluence of Gorner- and Grenzgletscher (Valais).

Gornersee is particularly well suited for this study. Hydrographs from the proglacial river Gornera were recorded since 1967, giving information on the time of the onset, duration and peak flow of the floods occuring every summer. In the past, glacier floods from Gornersee caused damage in Zermatt and Täsch. Thus, a detailed study of this ice-dammed lake and its drainage is not only of interest in basic glaciology but also for practical reasons. In the past, theory and numerical models of water flow in ice-walled conduits advanced substantially. In addition, techniques to observe glacier dynamics and its short term variations became available. For these reasons, it became possible and timely to produce a comprehensive set of data on glacier floods and to interprete them realistically.