How climate warming is affecting New Zealand mountains
In 1882 the Austrian Robert von Lendenfeld visited the Mount Cook area. On his way to climb Hochstetter Dome he sketched the vast expanse of the Taman Glacier.
The artist is viewing the Tasman Glacier from the moraine on the eastern side of the glacier where the Murchison Valley meets the Tasman Valley. The Ball Spur is right opposite. The glacier ice reaches almost to the top of the moraine.
Lower Tasman Glacier as seen from the Ball Spur. There was no terminal lake in 1976. First small pools appeared in 1978. As soon as a lake appears that is in touch with the ice it spells the demise of the glacier. Melt back accelerates dramatically until there is no more ice in contact with the water.
Water is most dense at 4.2 °C and sinks to the bottom where it gets in contact with the ice. Ice melts, cools down the water, the colder water rises to the surface and gets heated up again by the sun. The lake acts as a giant solar collector, the sun's energy has unhindered access to melt the glacier ice below. Where there was solid ice in 1976 there is a 5 km long lake now.
It is estimated that the lake will be 10 km long in another 10 years time.
A retreating snow line exposes the ice underneath. Melt channels and crevasses form, accelerating the downwasting of the ice on the Tasman Glacier (left).
A downwasting Tasman Glacier exposes increasingly high moraine walls. Access to the side valleys, the Beetham and Reay Valleys of the Malte Brun Range, are being cut off (right).
Loss of glacier ice leads to a loss of pressure on the lateral moraine, which in turn collapses. In 1976 it was still possible to drive a vehicle along the road to Ball Hut. Now te road has all but disappeared down the hill (left).
After moraine walls become exposed the side streams cut deep into the hill side. This can make traditional routes impassable, such as the Copland Track and access to Hooker Hut (right, circle).
The loss of lateral pressure on the bottom of the mountain leads to increasing instability further up the mountain. Slips and landslides become more likely. In 1991 a large landslide took out 13 million cubic metres of rock on the east face of Aoraki Mount Cook, lowering its summit by some 10 m (left).
Higher temperatures lead to a loss of perma-frost at increasing heights. This leads to more frequent rock fall on previously stable mountain faces. In March 2007 an almost continuous rock avalanche came off the Anzac Peaks near Aoraki Mount Cook for the duration of three weeks, undermining the top of the peaks. Given the geologically very young rock and its upfolding one can expect a larger event in the not too distant future (right).
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