Mount Rolleston (2271 m) is the highest peak within Arthur's Pass and is home to the South Island's northernmost glacier (Crow Glacier). The park's largest glacier, Marmaduke Dixon, is found near Mount Wakeman and covers an area of nearly 22,500 ha.
A glacier has several zones. Highest in altitude is its accumulation zone where fresh snow (nevé) accumulates and compresses underlying layers over time. This process creates forces that move the icy masses downwards into the next zone, the ablation zone. Here, the glacier moves along a less inclined slope, which causes more debris to be carved out along the way. Due to the debris and the change in altitude, parts of the ice start to melt. Once the third zone (terminal zone) is reached, partly melted ice may break off and/or forms glacial lakes and rivers. Experts say that it may take up to 300 years for ice to reach the terminal zone from the accumulation zone.
The life of a glacier is a constant process of retreating and advancement. Arthur's Pass glaciers reached their minimum around 6000 to 7000 years ago when the climate was warmer than today. It advanced again during the earth's little ice age within the past 500 years. Nevertheless, glaciers are generally known to shrink in size. Scientists believe that the reduction is a direct consequence of global warming that may cause New Zealand's temperatures to increase by at least 1°C by the end of the century.