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How are the Glaciers formed?
South Westland lies in the path of a band of wind known as the ‘Roaring Forties.’ The weather that flows on to the West Coast is forced to rise over the Southern Alps, thereby cooling and dropping most of its moisture as rain and snow. This process causes large quantities of snow to fall on the névé, or catchment area of the glacier every year.
Gravity squeezes the snow from the névé down the glacier valleys. The once fluffy snowflakes decompose and are compressed into the hard blue ice, hundreds of metres deep, that you can see in the lower icefalls. Forces generated by the moving mass of ice cause it to grind away at everything in its path to reach the terminal face at the front of the glacier. This is no lightning-speed process. It takes between 15 and 25 years for the snow to be transported from the névé to the terminal face.
Ever moving ice rivers
A glacier likes to find equilibrium and keep the amount of ice produced in the névé equal to the amount of ice lost to melting in its tongue. This results in the dramatic advances and retreats of the terminal face of the Fox and Franz Josef glaciers. The high snowfall continues to push ice down the valleys at very high rates.
This movement is aided by lubrication from the ice that melts under pressure between the glacier and the steep valley floor. This ice slides down hill to the more level river valley below, where it is still 300 metres thick. The glaciers flow over large bedrock steps on the valley floors. This causes the ice to extend and break up, forming steep icefalls that are mazes of crevasses and pinnacles of ice. Shelving in the valley floor deep beneath the glacier causes cracking, upheaval and deep ravines in the glacier surface, creating a dramatic and potentially dangerous frozen landscape. Surface melting occurs throughout the lower altitudes, feeding the frigid rivers that flow out the rocky ravines and on through temperate rainforests to the Tasman Sea. Both of these factors cause the Franz Josef and Fox Glaciers to have flow rates that are up to 10 times faster than most valley glaciers.
Spectacular views of this dramatic landscape are gained from short valley walks to the Franz Josef and Fox Glacier terminal faces, or by taking a guided walk on to the ice.