French Alps and Alpine Forelands
The French Alps are the western part of the 1,200-km-long Alpine range extending eastward to the Vienna basin. They have the highest summits of the range, in the Mont-Blanc massif (4,807 m a.s.l.). In France, the chain has an arcuate form, convex to the north and west. It lies between Lake Geneva (46° 25′ N) and the Mediterranean coast (approximately 43° 35′ N). The Rhône valley forms a clear geological and morphological western limit. To the north (towards the Jura range) and the south-west (towards the ridges of Provence) the boundary is not so well defined. The French Alps and Alpine forelands have been thoroughly studied for over a century by many researchers from the Universities of Grenoble, Lyons, Aix-en-Provence, Nice, and Chambéry. First, it is necessary to outline the great diversity of landforms in relationship to the complex geological history, tectonics, and lithology. The importance of the Alpine karst landforms and caves must be emphasized; studies of these forms have been extended substantially in the last twenty years and they give many new insights into the Plio-Pleistocene tectonics and climates of this region. The past and present role of glaciers is another important topic in this chapter. From recent studies, we now have a much better knowledge of the transition from the last glacial period to the Holocene. It was impossible to write a chapter on the Alps and ignore the fact that the inhabitants of the Alps have to cope with many permanent natural hazards. The chapter ends with a short synthesis of the main morphogenic systems, which characterize the French Alps and forelands. In the north, the climate is oceanic and precipitation is evenly distributed throughout the year. A high relief, with landforms oriented transverse to the general western atmospheric circulation, results in a great variety of regional climates: from west to east, the continental effect is marked by a decreasing precipitation at the same altitude. Exposure and altitude combine to create contrasting local climates. Temperature inversion is frequent, especially when cold air is trapped in deep valleys.