The Mer de Glace ("Sea of Ice") is a valley glacier located on the northern slopes of the Mont Blanc massif, in the French Alps. It is 7.5 km long and 200 metres (660 ft) deep but, when all its tributary glaciers are taken into account, it can be regarded as the longest and largest glacier in France, and the second longest in the Alps after the Aletsch Glacier.

I can no otherwise convey to you an image of this body of ice, broken into irregular ridges and deep chasms than by comparing it to waves instantaneously frozen in the midst of a violent storm.