The Aletsch Glacier is the largest glacier in the Alps, located in southern Switzerland in the canton of Valais. It is surrounded to the north by the Jungfrau massif, to the south by the Rhone Valley with which the glacier communicates via the Massa Gorge, to the east by Lake Märjelen and to the west by the Aletschhorn.
Its length is 23.6 kilometres (as of December 2001) with a surface area of 117.6 km2 (or 128 km2 according to the Unesco evaluation commission) and a mass of 27 billion tonnes of ice. Its middle part is advancing at a rate of 180 to 200 metres per year. Nine peaks surrounding it are over 4000 metres high with an average height of 4108 metres.
In 2001, UNESCO inscribed the "Swiss Alps Jungfrau-Aletsch" as a World Heritage Site, a site which partly covers the Aletsch Glacier.
It can be reached from Bettmeralp, a winter sports resort which in summer is the starting point for numerous hikes and which can be reached exclusively on foot or by cable car from Betten Talstation, or from Mörel or from Fiesch (Upper Valais).