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GLACIORISK Résumé de rapport

Project ID: EVG1-CT-2000-00018
Financé au titre de: FP5-EESD
Pays: Switzerland

Advice for conducting scientific studies about the various glacial hazards and test of various investigation techniques in different contexts

Glacier outburst floods (jokulhlaups) 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 (from hours to days). Jokulhlaups pose a significant hazard potential and have caused substantial damage in the past in the Alpes and elsewhere. The assessment and prevention of hazards related to jokulhlaups require a reliable prediction of the timing, duration and magnitude of the outburst flood.

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 jokulhlaups indicate that during the start of the drainage different physical processes may be important. Studies should be conducted to address some important open questions of the subglacial drainage process in a combined ?eld and numerical modelling project. In particular, the drainage of different glacier dammed lakes should be analysed with existing and improved models.

The second category concerns avalanches. Observations show that ice masses become detached from unstable glaciers by progressive fracture at englacial interfaces. Such events occur all around the year. The main difference between so called hanging glaciers and steep glacier tongues are that for hanging glaciers a progressive motion increase of an instable ice mass always leads to a major break off. For steep glacier tongues this happens only in very rare situations. Results from combined field and modelling studies on hanging glaciers show that a forecast of a major breaking off event is possible in some situations. However, it is still very difficult to predict in advance the breaking off volume. In most cases, an instable ice mass breaks off in many smaller chunks of ice. But even a small volume of falling ice can trigger a huge combined ice/snow avalanche if a thick and unstable snow pack exists around a hanging glacier. Such events can be relevant in the winter season and should be seriously considered by people responsible for the security of roads and railways in regions where hanging glaciers exist.

To improve forecasting possibilities of breaking off of instable ice masses, it is necessary to monitor the regular formation and detachment of ice chunks on hanging glaciers by:
- Monitoring the breaking off activities at the front of hanging glaciers with regular high quality photographs.

- Monitoring the evolution of the motion of the unstable ice mass from the beginning of the instability to the time of breaking off.

For hanging glaciers located in regions where the basal ice temperature is close to the melting point, their stability can change in near future because of global warming. This is because the transition of a previously cold to a temperate glacier base, basal sliding can suddenly be induced, leading to a major destabilisation of the hanging glacier. Where such an evolution is expected to happen and if human activities are endangered, a monitoring program for this type of hanging glaciers is extremely important for hazard assessments.

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Martin FUNK
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