Aoraki / Mount Cook - Geology

Geology

The Southern Alps on the South Island were formed by tectonic uplifting and pressure as the Pacific and Indo-Australian Plates collided along the island's western coast. The uplifting continues, raising Aoraki / Mount Cook an average of 7 millimetres (0.28 in) each year. However, erosive forces are also powerful shapers of the mountains. The severe weather is due to the mountain's jutting into powerful westerly winds of the Roaring Forties which run around approximately 45°S latitude, south of both Africa and Australia. The Southern Alps are the first obstacle the winds encounter after South Africa and Australia, having moved east across the Southern Ocean.

The height of Aoraki / Mount Cook was established in 1881 by G. J. Roberts (from the west side) and in 1889 by T. N. Brodrick (from the Canterbury side). Their measurements agreed closely at 12,349 feet (3,764 m). The height was reduced by 10 metres (33 ft) when approximately 12-14 million cubic metres of rock and ice fell off the northern peak on 14 December 1991. Mt Cook lies in the centre of the distinctive alpine fault, a 650 km long active fault in the Southern Alps. It is responsible for the uplift of Mt Cook and is considered to move every 100–300 years . It last moved in 1717.