While volcanic activities are a mountain’s building process, denudation processes are trying to level them down. Denudation includes processes which removes rock debris and carrying them to a new location. These processes happen through gravity, wind, ice and water. In the Tongariro Volcanic Centre, winds are an effective denudation agent because the mountain top gales are frequent and severe. Winds can transport and deposit debris. They carry with them fine silts and sand particles and depositing them downwind.
Material that is not protected by matted roots of plants, like tussock, is eroded by the wind leaving the plant isolated. Winds also distribute ash during eruptions. Since winds are usually westerly, ash deposits are the greatest east of the mountains. This also results in the area being prone to lahars and lava flows. On the east side of the mountain, lower rainfall and lack of vegetation makes the soils drier and easier for the wind to erode. The Chateau experiences 142 days of ground frost a year.
The fall of temperature as altitude increases causes the summit of Mt. Ruapehu to be below freezing point at any time. These conditions result in ice being an important agent of denudation, mass movement and erosion. Rocks that freeze at night may heat up and expand during the day. The sudden change in temperature may cause the rock to break. Conditions on the mountain also create ice needles. These push through the soil during winter nights, taking small soil particles and stones with them.
When the needles melt and collapse during the day, the removed particles will roll downhill, resulting in mass movement on a small scale. There are 18 glaciers in Mt. Ruapehu. E. g. Wangahu and Summit Plateau. Glaciers, which are huge bodies of ice, move downhill under the influence of gravity. As they move through the mountain, they tear away blocks of rock off of the floor and the walls of valleys, and wear away rocks beneath them. This is another form of erosion. Glaciers cause U-shaped valleys and over deepened valley floors to form.