Hydrogeology and palaeohydrography of the Saint-Flour planeze, French Massif central

The first aim of this contribution was to find new water resources to provi de correctly the developping town of Saint-Flour and the villages on the Pl aneze, northward. The application of a geophysical method, magneto-telluric s, complemented the first geological studies and after three drillings the initially estimated production of 200 m(3)/h was reached. In a second time the authors completed their data especially on volcanic vents and in their immediate surroundings. The more documented maps obtained this way, in part icular isoheights, isohypses and isopachs maps lead to the discussion of th e evolution of the drainage pattern in relation with volcano-tectonics and glacial events. In conclusion the hypothesis of Ph. Glangeaud [1922] by the terms of which the Truyere river flew into the Alagnon and the Allier (Loi re basin) before its capture by the Lot (Garonne basin), was confirmed. The y have also contributed in finding an old bed of the Alagnon under the Plan eze.