Mountain Erosion

Mountain erosion storm. Image: Julian Thomson.

Image: Julian Thomson.

The tectonic forces that lead to mountain building are continuously countered by erosion due to intensified precipitation, wind and temperature extremes. These elements, aided by the force of gravity, are particularly powerful along the mountain ranges which form a barrier to the prevailing westerly winds that buffet New Zealand.

Imagine all the elements at work in an intense storm in the mountains. Gale force winds, lightning strikes, temperature extremes and a deluge of snow, hail or rain. These combined forces break up the rocks and erode the peaks into their stark, sculpted forms.

Falling ice, rocks and gushing water wear away at the mountain slopes. The ice and rock debris accumulates in the valleys and flows downwards as slow moving glaciers. When these melt, piles of rock debris called moraines are left behind.

  • Aprons of rock debris make up the scree slopes alongside the Mueller Valley near Mount Cook. Image: Julian Thomson.

    Aprons of rock debris make up the scree slopes alongside the Mueller Valley near Mount Cook. Image: Julian Thomson.

    Strong winds pick up dust and abrade exposed rock surfaces.
  • Lightning instantly vaporizes water and ice in rock fissures and literally blows rocks apart.
  • Temperature changes thaw out and refreeze the ice in rock fissures, wedging them apart, whilst thermal expansion and contraction disintegrates exposed rock surfaces.
  • Rock falls and ice avalanches scour mountain sides, further eroding the slopes.

The powerful earthquakes that are responsible for the uplift of New Zealand’s mountains also destabilise them, causing many rock falls and avalanches that help to wear them down.

VIDEO: Big Avalanche on Mt Sefton - Watch the destructive power of falling ice!