chamonix, the aiguilles des drus and the aiguille verte, in the montblanc massif during summer

abrupt alpine alps altitude avalanche blanc bonatti cause chamonix climb climbing decline dramatic drus during environement exploration extreme frost glace glacier global haute history ice iconic icy landmark landscape limits mer mont monte mount mountain mountains nant natural nature overlook panorama panoramic peaks performance pioneer pollution rhone rockslide rocky savoie scenery site sky snow summer summit sunset threatens tourism travel valley verte walter warming