The geological roots of the Mont Blac massif

At dusk Lac de Cheserys, above Chamonix in the French Alps, is reflecting the Mont Blanc massif. The moon is rising above the jagged peaks of Les Grandes Jorasses and first stars are already visible in the quickly fading light.
During nightfall, approximately 45 minutes after sunset, the twilight sky shows a distinctive deep blue color caused by the ozone layer aloft. The last sunrays travel parallel through the atmosphere at 16 miles (25 km) height. The ozone absorbs all colors of the spectrum except for the blue short wavelengths. The rising moon lights up the mountains while the first stars become visible in the deep silence.
The rocks that build up the panorama of the Mt. Blanc massif (15780 ft, 4810 m) in the French Alps have a geologic history that dates back to the Carboniferous to Permian age 300 million years ago. At this time all landmasses were united into the super-continent Pangäa. The Variscan mountain chain formed along Pangäas continental collision zones between Africa, Eurasia, North- and South America. During the eons of time this mountain range was completely eroded. The only remaining rocks are the crystalline basement of the subsurface consisting of Granite. During the Mesozoic age of the dinosaurs, this granite basement was covered by ocean sediments up to a thickness of several miles. About 40 million years ago, the mountain uplift of the Alpine orogeny began with intense uplift phases 22 and 12 to 5 million years ago. The granite basement of the former Variscan orogeny was uplifted into a dome structure while the overlaying soft sediments eroded completely. This caused a relaxation leading to further uplift of the granite body.
Finally, the glaciers of the last ice age cycles formed today’s relief of the impressive Mt. Blanc massif.