Glacier Noir     The Glaciers Noir and Blanc are the largest in the area. They are approximately 6 km long and are very contrasting. In colder periods they used to be joined up. The glaciers have been surveyed since 1815. At first only the position of the glacier snout was recorded, but since 1921 two cross profiles have been surveyed to measure annual changes in ice thickness. A thick layer of deposits protects the snout of the Glacier Noir from melting. There are 25-35 cm of deposits over much of the lower part of the Glacier Noir and in some places the sediments are at least 6m thick. At an altitude the Glacier Noir has 2-3m of melt a year, while the Glacier Blanc has 5-6m of melt. The Glacier Noir is thus protected from the suns rays by these sediments. The upper section of the Glacier Noir Studies suggest that the glacial regimes of the Glaciers Noir and Blanc are explained by:- The amount of winter precipitation (5%). There is little variation in this and so this only accounts for 5% of the changes in ice budget. The amount of summer precipitation (16%). July/August temperatures (56%), the most important factor. The rest (22%) is unexplained. The total correlation explains 77% of the variation of the glacier.