New Zealand is in the temperate latitudes between 35 and 50 degrees south. It is part of a weather cycle in which warm, low pressure air from the equator meets cold, high-pressure air from the South Pole. This is known as the Roaring Forties. It starts when Antarctic winds travel north away from the pole towards the warmer ocean, gathering speed and becoming katabatic winds. As they travel north they meet the warmth of air that has travelled south from the equatorial regions. This forms a low-pressure system that results in westerly winds which have constant and high speed. Consequently the lands in the path of the Roaring Forties experience heavy rainfall on the western side (South Chile, Australia, New Zealand). New Zealand has enough rain on the western side to sustain a rain forest.

Ventifacts

Like many rocks and stones, ventifacts are formed by erosion. Instead of becoming smoother and more rounded over time, ventifacts become ridged and develop defined sides (facets) over time, due to an unusual form of erosion. The wind picks up small particles of sand (and, in the case of Antarctic examples, ice), and blows them against the rock, slowly shearing off small pieces of the rock and resulting in the formation of a facet. More than one facet occurs when there is more than one common prevailing wind direction or if the ventifact gets turned around at some point in its formation.