The glacier caves of Gornergletscher (Switzerland): preliminary notes on their morphology and hydrology

Abstract

In the last 15 years, several investigations in englacial and subglacial caves have been performed in the Alps. The most interesting results have been obtained from Gornergletscher, in the south-west of Switzerland, one of the widest glaciers in the Alps. It descends towards WNW from the Monte Rosa group, receiving important tributaries from the left. In the ablation zone, between 2,600 and 2,400 m of altitude, the glacier exhibits a karst-like topography. In this area the surface is relatively planar and only a few fractured; this morphological condition allows the surface drainage of meltwater. Some streams feed supraglacial lakes, most of which have no surface outflow. Meltwater from supraglacial basins often plunges down into vertical holes (moulins) which feed directly into the englacial drainage network. Presently, the surveys have allowed us to recognise two different types of moulins: the former is characterised by a vertical pattern, with a first shaft commonly deeper than 40–50 metres; the latter has a gently dipping development with a small shaft at the entrance. Some of the first type glacier shafts have been explored to the water-table (varying from –30 to –140 m). On the ground of our observations, the initial geometry of moulins depends on local structural factors, whereas the annual evolution mainly depends on the hydrodynamic behaviour and on the seasonal water-level fluctuations. Geometry and hydrology of englacial caves are very similar to those of karst rock; this morphologic convergence and the hydrodynamic behaviour of moulins suggest the existence of a complex englacial “phreatic” network.