Dynamics of alpine glaciers large instabilities: results and open problems

The study of glacier instabilities can be very useful, particularly when the activation of large ice avalanches can be dangerous for several elements at risk down-valley. This critical condition characterizes a growing number of glaciers in the Alps, where the distance between infrastructures, tourist areas and glaciers are minimal. The tragedy that occurred in Marmolada in 2022 is an example of the impact that an ice avalanche can have on a highly frequented area. In several recent studies, glacier-related instabilities are based on approaches similar to the ones adopted for landslides; in particular, the use of high-rate monitoring systems is fundamental for a characterization of the surficial movement of the glacier and its activity. The presence of an acceleration phase is often a precursor of the fall of the unstable ice chunk, and that is why the use of high-rate monitoring systems can be adopted for early warning purposes. The availability of similar data also allows a deeper knowledge of the processes that characterize the evolution of glaciers. Up to the present, the limited presence of permanent survey systems has prevented a more detailed study of the dynamics that control the evolution of glaciers. Recent monitoring solutions adopted to manage the ice-avalanche-related risk in the Alps represent an excellent opportunity to reduce this gap. The Grand Jorasses (Italian side of the Mont Blanc massif) open-field laboratory for the development of monitoring systems is an interesting example of this recent opportunity. The presence of cold (Whymper serac) and temperate (Planpincieux glacier) monitored glaciers is also important for better evaluating the impact of water at the bedrock-ice interface on the stability of hanging glaciers. The results obtained in the Grand Jorasses open-field laboratory pointed out the high complexity of temperate glaciers due to the variety of triggers that can activate large ice falls. The restricted access to the site for safety reasons limited the direct measurement of important parameters and led to the adoption of proximal remote sensing solutions. Thanks to the acquired data, a conceptual model of the glaciers' dynamics have been developed and adopted for better risk assessment.