Aiguille Verte, Massif du Mont Blanc (photo Mark Trengove)
The French portion of the range includes the highest summit in Western Europe, and most prominent summit in Western Europe – Mont Blanc (4808m), with 4695 metres of prominence.
The French Alps were pushed up against the Massif Central block to the west during the Alpine Orogeny. They are folded and overthrust mountains, sharpened by frost and eroded by glaciation and running water. There are two main types of rock structure. The central core of the High Alps is composed of Palaeozoic crystalline rocks, with violently folded metamorphic rocks around the edges of the core area.
The French Alps can be divided into four geological sections, all running in parallel on a mainly north-south orientation:
· The High Alps. This section is about 100km in width, and mainly follows the Franco-Italian border. The High Alps are structurally very complex, especially in the south-east, with folding, overthrusting and nappe formations. Crystalline massifs form the highest ranges. These ranges are composed of a great variety of rocks, including granite, gneiss and schist. The highest summits are found here, particularly in the Mont Blanc and Écrins Massifs.
· The Longitudinal Trench. This is composed of the vale of Chamonix and the valley of the River Isère between Albertville and Grenoble. It is only about 5km wide and is several thousand metres lower than the mountain ranges which flank it. The trench is formed of soft shale, rapidly eroded by the fast-flowing rivers that drain the mountains around it.
· The Pre-Alps. These ranges stretch from Lake Geneva to the River Durance. They are mainly composed of limestone and are generally half the altitude of the High Alps. They are bisected by four main cluses (deep valleys with steep sides) which once held rivers but now contain large lakes such as Lake Annecy.
· The Alpine Foreland (The Dauphiné). This area lies between the Rivers Isère and Rhone at the western foot of the Pre-Alps. It is mainly covered in deposits of pebbles and clay washed down from the Ice Age glaciers. There are moraines, rock basins and outwash material which have been terraced by the action of rivers.
The French Alps have been, and are still being, moulded by glacial action. The High Alps were much affected by the Écrins ice cap in the last Ice Age. The ice flowed south and then west down the valley of the Durance. After the ice ages, vast amounts of meltwater flowed west and south off the melting ice caps for hundred of kilometres to the Mediterranean Sea. As the weight of ice lifted off the mountains, they rose in altitude. They are still rising to this day, although the rate has slowed to the extent that they are being eroded as fast as they rise. Glaciers still exist today, but they are receding rapidly as global warming takes place. The glaciers today are valley glaciers like the Mer du Glace below Mont Blanc, or cirque or niche glaciers.
The highest, and most prominent mountains in the French Alps are Mont Blanc itself and Barre des Écrins (4102m) , with a prominence 2045 metres.
See below for lists for the French Alps published so far. More will be added in due course.