It is the Titan among the alpine glaciers, a tremendous chunk of ice: The Great Aletsch glacier is the heart of the UNESCO World Heritage site Swiss Alps Jungfrau-Aletsch. John Tyndall wrote in 1860: "The Aletsch glacier is the most magnificent glacier in the Alps: we stood above him, while the surrounding mountains fed abundantly the mighty stream". With an area of 81,7 km2 and a length of 22,6 km, it is the largest and longest glacier in the Alps. Imposing four-thousand meters high peaks as the Jungfrau, the Mönch and the Grosse Fiescherhorn surround it and limit its accumulation zone to the north; the firn fields of the Grosser Aletschfirn, Jungfraufirn, Ewigschneefäld and Grüneggfirn (from west to east) flow together at the Konkordiaplatz. At the seams they form the starting point of the powerful, elegantly curved medial moraine that characterizes the image of the great ice stream.