In the North Island there are seven small glaciers on the slopes of Mount Ruapehu, an active volcano (9,175 ft). Their size varies, but they are usually less than a mile in length and descend to about 7,000 ft above sea level. During the winter ski-ing period the Whakapapa Glaciers, near the Chateau Tongariro, are visited by several thousand people each week.
In the Southern Alps more than 360 glaciers have been named; they occur between 43° and 45 South latitude, and have a total area of 330 sq. miles. The major ones are located in the area around Mount Cook, the highest mountain in New Zealand (12,349 ft). Draining to the eastern side of the Divide, into the Waitaki River system, are the following glaciers: Godley (6.5 miles long), Hooker (6.5 miles long), Mueller (8 miles long), Murchison (9 miles long), and Tasman (17.5 miles long), their total area being 91 sq. miles. The two largest glaciers draining to the western side of the Southern Alps are the Franz Josef (7 miles long), and the Fox (8.5 miles long); their total area is 16.5 sq. miles.
Other glaciers lie north of the Mount Cook region, in the Rakaia-Rangitata River systems, the largest being the Ramsay and Lyell in the Rakaia catchment area. A further group is centred around Mount Aspiring (9,957 ft), 100 miles south-west of Mount Cook. The largest, the Bonar, Volta, and Therma, rise on the slopes of Mount Aspiring itself, and many smaller glaciers are clustered around the headwaters of the Arawata, Matukituki, Dart, and Hollyford Rivers. The eastern glaciers have a fairly gentle gradient and descend to between 2,500 and 3,500 ft above sea level; the western glaciers are much steeper and their terminals are as low as 1,000 ft above sea level, well down into the thick rain forests.
Glacier-movement measurements were first made in the Mount Cook region in 1889 by T. N. Brodrick . Rough estimates made by A. P. Harper of surface speeds of the Franz Josef Glacier in 1894 indicate very high rates of flow of 100 to 200 in. a day up to 2 miles from the terminus. Rates on the Tasman Glacier vary, being only about 20 in. a day from a point 7 miles up stream from the terminal. The glaciers are fed by snow brought to the Southern Alps by the prevailing winds off the Tasman Sea; total yearly snowfalls at the higher elevations (6,000–8,000 ft) vary from 10 to 20ft. The steeper West Coast glaciers have little moraine carried on their surface and have shown a marked terminal retreat in the last 10 years. The Franz Josef Glacier terminal, for example, has retreated three-quarters of a mile. The large glaciers on the eastern side of the Southern Alps are mantled with moraines, and lower parts of the glaciers have been reduced in thickness by up to 200 ft, with some terminal retreat.