摘要
The Miage Lake is an ice-contact lake located on a side of the Miage glacier (Monte Bianco Massif, Alps), the third Italy’s largest glacier, and is characterized by rapid drawdown episodes that have occurred with varying frequency in the lake’s history. The emptying episode of September 2004 gave the possibility of performing many activities, up to the filling phases which occurred during spring and summer 2005. In situ tests and measurements and laboratory tests lead to a reliable reconstruction of the path of water recharge and draining and to the development of a numerical model of unsaturated-saturated groundwater flow to evaluate natural losses through the lake bed sediments. Results show that material at the bed of the lake has a low permeability and can be responsible for water losses of a few litres per second, very far from the discharge calculated during the rapid drawdown episodes. These results gave the experimental and numerical evidences to support the hypothesis that identifies sudden and temporary failure in the ice floor as the only possible cause of the rapid draining events historically occurred in Miage Lake. In the monitoring period the hydrological balance has also been assessed to evaluate the factors affecting the main recharge phase of the year. Calving was found to be the most important factor contributing to recharge, followed by direct melting and precipitation while water losses occurring through the lake bed sediments and evapotranspiration are much smaller even if not negligible.