Aletsch (äˈlĕch) [key], glacier, 66 sq mi (171 sq km), 16 mi (26 km) long and 1.2 mi (1.9 km) wide, S central Switzerland, largest in the Alps. It lies between the Jungfrau and the Aletschhorn, one of the highest (13,721 ft/4,182 m) peaks in the Bernese Alps.
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