Mangatoetoenui Valley, north of the Rangipo Desert. Photo NC.

This large valley drains the north eastern slopes of Ruapehu and is also a known lahar path.
The Rangipo Desert is in no way associated with lack of rain. On the contrary the annual rainfall, ranging between 1500 and 2500 mm (59 and 98 in.), is plentiful. The major causes that have shaped this environment are thought to include:

• fragile soils of volcanic ash and gravel that are quickly eroded as soon as the vegetation cover is destabilised. Once erosion sets in it is very difficult for plants to get a new hold.
• Vegetation destruction by repeated fires of volcanic origin, as well as those caused by humans. Also grazing by introduced mammals: sheep, cattle, rabbits and hares.
• Harsh climatic conditions due to altitude, especially a high number of days with frost, resulting in a weak vegetation cover. Further adding to this are the strong winds that blow through the saddle between Ruapehu and Ngaruhoe, in the rainshadow of the volcanoes, and their strong dessicating effect on the ground.