mountain range on South Island, New Zealand. It is the highest range in Australasia. Making up the loftiest portion of the mountains that extend the length of the island, the Alps extend from Haast Pass, at the head of Wanaka Lake, northeastward to Arthur's Pass. They vary in elevation from 3,000 feet (900 metres) to 16 peaks above 10,000 feet (3,050 metres) and culminate in Mount Cook (Cook, Mount) (12,316 feet 【3,754 metres】). Glaciers descend from the permanently snow-clad top of the range, and major rivers, including the Rakaia (Rakaia River), Rangitata (Rangitata River), and Waitaki (Waitaki River), drain eastward across the Canterbury Plains. The Alps divide the island climatically, the forested western slopes and narrow coastal plain of Westland being much wetter than the eastern slopes and the wide Canterbury Plains. The Southern Alps have great hydroelectric potential, and, since the 1930s, power stations have been built on the Waitaki River and its tributaries and at Lake Coleridge. The Alps are crossed by a rail line passing through the Otira Tunnel (5.3 miles 【8.6 km】 long) at Arthur's Pass. Sighted by the Dutch navigator Abel Tasman (Tasman, Abel Janszoon) in 1642, the Alps' first European traversal (1857) was accomplished by Leonard Harper, first president of the New Zealand Alpine Club.