The Franz Josef and Fox Glaciers of New Zealand’s Westland National Park are remembered by visitors for the extraordinary sights of glacier ice within the forest zone. From freezing conditions near the mountain crests the glaciers slowly grind their way down-valley into warmer temperatures far below the upper limit of forest. It may seem a contradiction that such glaciers occur in a temperate climate, and that ice and forest are juxtaposed, but there are simple reasons.
What is a Glacier?
Why are there Glaciers on a South Pacific Island?
Why is there ice in a temperate Rain Forest?
The movement of a Glacier
With the continual addition of snow to the neve, snow and ice move downward into the glacier, everything on the surface becoming buried deep within the ice. Further down the glacier at the trunk (just below the neve) the flow of ice attains its maximum speed. In the icefalls of the Franz Josef and Fox glaciers rates of up to 4m per day have been recorded, which are very rapid by world standards. For example, in 1943 an aircraft crashed on the Franz Josef Glacier about 4km up from the terminus. Six years later parts of the wreckage appeared at the glacier front.
Lower down the trunk the rate of flow slows as more and more ice melts in the warmer conditions. Here ice flows becomes directed towards the surface to replace ice melted from above. This flow brings rock debris from within the glacier to the surface, where it accumulates as moraine. General movement is in the direction of the banding within the ice. Near the Termius nearly all the ice has been lost, and most of debris from inside the ice now lies on the surface. Though the glacier front may be stationary, the ice near the Main Divide carrying greywacke rock from this area into the schist terrain at the glacier terminus.