The Alps were born 770 million years ago. An upheaval of the earth's crust raised a mass of schist, gneiss and limestone to form underlying layers of the Alps range. Towards the end of this upheaval, around 300 million years ago, intrusions of granite in the western sector of these ancient mountains brought with them metamorphic rocks which together formed the base of what we know now as the Mont Blanc and Aiguilles Rouges massifs.
Following extensive erosion and inundation by the sea when sedimentary rocks were laid down, this part of the Alps underwent a new phase of elevation as violent movements in the continental plates produced great mountain building creases in the earth's crust.
The formation of Mont Blanc
The formation of the Mont Blanc Massif was completed towards the end of the Tertiary era, some 15 million years ago.
Four succesive glaciations formed in the Quartenary era (an ice age) and helped to sculpt the present profile of the Mont Blanc range, excavating the Chamonix valley. At one time Chamonix was buried under a large expanse of ice, 1000m deep, which stretched as far as Lyon.
Finally the climate became milder, and the glaciers retreated to higher altitudes. This is the period we are living in now. Although retreating, the glaciers still play a major role in erosion.
Other erosion factors are:
- The freeze/thaw cycles of moisture in the form of ice frost and snow, which can split and flake rock
Meltwater and rain scouring channels down mountainsides and carrying with it boulders, stone and sediment.
- Wind, which displaces already loose material.
- Avalanche and Landslip flattening and changing land drainage patterns.
- Man, whose feet, wheels, activities, pollution and constructions still play their part in modifying the environment.