Landslides

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What is a landslide?

A landslide is a mass movement of rock, soil and other earth material down a slope. They can be very large (such as a landform at Te Kauri on the West Coast believed to be a large ancient landslide), or small, affecting a limited area. Landslides also include debris flows.

Landslides occur when unstable rock and soil on steep slopes are disturbed by earthquakes, heavy rain or activities such as mining or road construction. The diverse nature of the Waikato region’s landscapes produces different types of landslides in different areas.

Climate change is projected to increase the frequency and intensity of heavy rainfall events. This is likely to lead to more erosion and landslides, as much of the soil in the region is volcanic and prone to erosion.

Landslides in the Waikato region

Landslides are more likely to occur on areas of land steeper than 45 degrees. In our region these areas include:

  • the West Coast south of Port Waikato
  • the King Country
  • the Coromandel Peninsula
  • numerous other hill country districts.

These areas have an increased chance of slope failure if other factors such as high rainfall, accelerated soil erosion, unstable basement rock structure or earthquakes increase the risk.

In the past, landslides caused by the geothermal alteration of the soils in the Hipaua Cliffs near Little Waihi have covered the area, while larger cliff failures have caused soil and rock flows that created over eight hectares of new land at the southern edge of Lake Taupo.

Landslide types

Landslides can be divided into groups according to their type of movement and material. Types of movement include falls, slides and flows, and types of material include rock, debris and earth.  For more information on landslide types you can visit the USGS website.

Landslide mitigation

Landslide mitigation is difficult and often expensive as it requires identifying the reasons behind the movement and reducing risks to human life through engineered options or changes in land use.

Landslide mitigation options include:

  • Discouraging building and other development in ‘at risk’ areas.
  • Warning signs where the landslide risk cannot be reduced.
  • Appropriate tree planting
  • Slope drainage to reduce pressure from ground water.
  • Removing material to reduce the angle of slope, making it less likely to slide, or removing unstable material
  • Other engineered options such as rock-bolting, retaining walls and rockfall fences.