Fed by four alpine glaciers, Fox Glacier falls 2,600 m (8,500 ft) on its 13 km journey from the Southern Alps down to the coast, with it having the distinction of being one of the few glaciers to end among lush rainforest only 300 metres (980 ft) above sea level. Although retreating throughout most of the last 100 years, it has been advancing since 1985. In 2006 the average rate of advance was about a metre a week. In January 2009, the terminal face of the glacier was still advancing and had vertical or overhanging faces which were continually collapsing.
The outflow of the glacier forms the Fox River. During the last ice age, its ice reached beyond the present coastline, and the glacier left behind many moraines during its retreat. Lake Matheson formed as a kettle lake within one of these
