Saturday, March 22, 2008

The Tasman Glacier

The Tasman glacier is close to New Zealand's biggest mountain Mt. Cook. The glacier looks more like a giant quarry than New Zealands biggest glacier. The rock rumble strewn across this hummocky landscape, called the 'surface moraine', is usually only a metre or two thick. Beneath it there is still a great dept of glacial ice - about 200 metres of it at the head of the lake rising to as much as 600 metres thick as you look into the distance some 9km away.

Like all glaciers in temperate parts of the world the Tasman glacier has been shrinking rapidly over the last century losing about 0.5% of its total volume each year. The accumulation of surface moraine is one consequence of this ice recession; so too is the down-wasting of the surface of the glacier and the formation of the rapidly enlarging terminal lake. Twenty yeears ago this new 'Lake Tasman' was little more than a scattering of sink holes. And 100 years ago you would have had to have been above where this photo was taken from to get onto the glacier surface.

All of the large natural lakes in the McKensie Basin were all created in much the same way when huge ice glaciers issuing from the Mt Cook region began retreating some 14000 years ago. Prior to that the Tasman Glacier had advanced to a maximum length of 85km with an ice surface 700 metres above the point where this photo was taken.

Tasman Glacier: Length 29km; Area 101km square; Maximum speed about 200metres a year (recorded near the head of the glacier).

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