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Mer de Glace
From Wikipedia, the free encyclopedia
The Mer de Glace (Sea of Ice) is a glacier located on the northern slopes of the Mont Blanc massif, in the Alps. At 5.6 km long and 200 m deep, with an area of about 40 sq km, it is the second-longest glacier in the Alps, after the Aletsch Glacier.
It originates at an elevation of 3,900 m, and descends to 1,400 m. It was once easily visible from Chamonix, but has been shrinking and is now barely visible from below.
It is in the Chamonix valley, it was the first place in the valley to have a custom-made tourist attraction.
The Mer de Glace, like all glaciers, is constantly renewed under the effect of two phenomena: accumulation, notably due to snowfall and ablation, essentially due to melting. The Mer de Glace flows permanently under the effect of its own weight, crusting crevasses, seracs or pockets of water to form, depending on the type of ground.
The glacier's speed, although not perceptible to the naked eye, is considerable. From more than 120 meters a year in its upper part, the Mer de Glace moves about 90 meters per year in the region of Montenvers, which is about one centimeter per hour.
As soon as the tensions intensify, the glacier is deformed and crevasses appear. These are notably transversal. When there is intense crevasse activity, the breaking-up of the glacier by the crevasses forms blocks of seracs.
The unidentified objects, of variable depth, depending on their positioning, may reach fifty metres. They always form in the same place because of the shape of the glacial valley in which the glacier flows. Disappearing downstream, they are renewed upstream.
Four other glaciers are sometimes, perhaps erroneously, included as part of the Mer de Glace; they are the Glacier de Telèfre, the Glacier de Leschaux, the Glacier du Tacul, and the Glacier du Géant.
Subglacial waters from the Mer de Glace are used seasonally by Électricité de France for the generation of hydroelectricity. Tunnels bored under the glacier collect water from the base of the glacier and channel it down to a hydropower plant in the valley. This water is then discharged into the Arveyron further downstream.
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