Haast Pass (1,842 ft) is the first low pass in the Main Divide of the Southern Alps south of Mt. Cook, over 50 miles to the north. Although the pass had long been known to the Maoris and was the route used by the war party of Te Puoho, it was not until 1861 that it was reached by a European, J. H. Baker, a surveyor. The first European to traverse the pass was Charles Cameron, a prospector, who crossed it in January 1863, a few weeks before Haast made his transalpine journey to the West Coast. For some years Cameron's claim was doubted; the point, however, was settled in 1881 when T. N. Brodrick discovered Cameron's powder flask at the summit of Mt. Cameron, to the west of the pass.
The low altitude of the pass is due to glacial diffluence during the late Pleistocene ice-age. The high precipitation of snow on the western side of the Main Divide must have built up the level of the glacier in the Upper Haast Valley until part of the ice flowed south across the divide into the Upper Makarora Glacier. Evidence of such origin is supported by the typical glaciated U-shape of the Haast Pass.
The rocks of the Haast Pass are mica schists similar to those in neighbouring parts of Westland and Otago. The belt of schists crossing the pass is generally finer-grained and softer than the general average and this may have been a determining factor in establishing the pre-glacial drainage and the location of the pass. The sequence of schists and gneisses now traversed by the Haast Pass Road is one of the most complete and interesting exposed anywhere in Otago or the Alps and has received detailed attention from geologists both before and after completion of the new highway. These examinations have led to the development of new theories on rock metamorphism that have been widely applied to other parts of New Zealand and also to similar schist terraces overseas.
by George William Grindley, M.SC., New Zealand Geological Survey, Lower Hutt.