The Southern Alps is a mountain range which runs along the western side of the South Island of New Zealand. It forms a natural dividing range along the entire length of the South Island. The term "Southern Alps" generally refers to the entire range, although separate names are given to many of the smaller ranges that form part of it.
The range is often known in New Zealand as the Main Divide, as it effectively separates the more heavily populated eastern side of the island from the west coast. Politically, the peaks of the Southern Alps form the boundary of the Canterbury and West Coast Regions.
Location and description
The Southern Alps run 450 km north to south. The tallest peak is Aoraki/Mount Cook, the highest point in New Zealand at 3,754 metres (12,316 ft) and there are 16 other points in the range that exceed 3,000 metres in height. The mountains are cut through with glacial valleys and lakes. According to an inventory conducted in the late 1970s, the Southern Alps contained over 3000 glaciers larger than a hectare, the longest of which – the Tasman Glacier – is 29 kilometres in length down towards Lake Pukaki. A chain of glacial lakes are found on the eastern side of the ridge from Lake Coleridge in the north to Lake Wakatipu in Otago in the south.
Settlements include Maruia Springs a spa near Lewis Pass, the town of Arthur's Pass and some lakeside resorts.
The Southern Alps were named by Captain Cook on March 23, 1770, who described their "prodigious height". They had previously been noted by Abel Tasman in 1642, whose description of the South Island's west coast is often translated as "a land uplifted high".
The Southern Alps lie along a geological plate boundary, part of the Pacific Ring of Fire, with the Pacific Plate to the southeast pushing westward and colliding with the northward-moving Indo-Australian Plate to the northwest. Over the last 45 million years, the collision has pushed up a 20 km thickness of rocks on the Pacific Plate to form the Alps, although much of this has been eroded away. Uplift has been fastest during the last 5 million years, and the mountains continue to be raised today by tectonic pressure, causing earthquakes on the Alpine Fault. Despite the substantial uplift, most of the relative motion along the Alpine Fault is sideways, not vertical.
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