Bogs, bluffs and waterfalls: the western side of Ruapehu. Photo NC.

The whole western side of the mountain is dominated by water, in sharp contrast with the eastern side where water and vegetation are nearly entirely absent.
Above the treeline little tarns and ponds such as this one are common. Their water is usually rich in iron compounds leached by the soil acids, and the plants growing in the pools are often coated in iron oxides.
The high bluff visible here with the waterfall in the background is Te Kohatu.