Abstract:
The karst of Moucherotte/Pic Saint-Michel (Vercors, Isère, France) - The massif of Moucherotte-Pic Saint Michel is located in the northeastern corner of the Vercors, in the area of Lans-en-Vercors and Saint-Nizier-du-Moucherotte. As anywhere in Vercors, this area is strongly marked by a dense karst relief. It harbours underground systems. Recent dye tracings (respectively from Sierre shaft, Choucas shaft, and Ira's Hole) allowed to determinate precisely the boundary of the catchment of the source called Bruyant. This basin spreads out from the Moucherotte to the Pic Saint-Michel, thus including a surface of 12km2. This is confirmed through the water balance. Of the 1600mm of yearly rainfall, 70% is infiltrated toward the source of the Bruyant. The water is conveyed through a main drain, probably mostly vadose, at the base of the recumbent fold. The landscape is due to the Quaternary processes. The two great landslides of "col de l'Arc" and of "Peuil" date back to this time. The glaciers have sculptured huge "combes" where many caves open, ancient places where sub-glacial waters were swallowing. These sub-vertical caves (which can measure up to 300m deep) with shafts and meanders, flow through large horizontal galleries older than the Quaternary (Combe Oursière shaft, Vallier cave…). These galleries, hidden away in this huge limestone mass, are the witnesses of an earlier and very elaborate subterranean drainage. This system is entirely different from our present drainage system.