Landslides

Key Messages About Landslides

• Landslides occur when sloping ground becomes unstable and rock, soil or vegetation fall down a slope.
• Landslides are commonly classified by the material involved (e.g., rock, debris, soil or mud) and the way they move (e.g., fall, topple, slide, spread, or flow)
• Landslides cause more deaths than any other geological hazard in Aotearoa New Zealand. They can cause significant damage to buildings, roads and other infrastructure. They can also dam rivers and if the dam fails, this can result in flooding downstream.
• The impacts of landslides can be reduced by land use planning, avoiding building on or near unstable land, strengthening the site through engineering solutions and carefully monitoring land for signs of movement.
• Although landslides may be triggered by a number of factors, they are most often triggered by earthquakes and heavy rain.
• If a landslide occurs – or you see any signs that the ground is unstable – evacuate immediately. If lives are in danger dial 111. Otherwise, seek advice from your local council once you are in a safe location.
• Reduce your personal risks – after heavy rainfall, don’t drive unless absolutely necessary and stay away from areas where landslides have occurred previously.
• Seek expert advice from a chartered professional geotechnical engineer if you are planning on excavating or building on steep slopes or believe the site may be affected by landslides.
• Make and practise your emergency plan, have a grab bag and emergency supplies.
• If you learn or suspect that a landslide is occurring or is about to occur in your area: Evacuate immediately, away from the potential slide area if it is safe to do so. Getting out of the path of a landslide or debris flow path is your best protection.
  • If you are in a property that could be or is being impacted by landslide debris move to the side of the house furthest from the landslide. This is likely to be the safest location within the property.
  • Take your pets with you, and move livestock to safe paddocks, if you can do so without endangering yourself.
  • Alert your neighbours. They may not be aware of the potential hazard. Advising them of a threat may save their lives. Help neighbours who need assistance to evacuate if you can do so without putting yourself in danger.
• During a severe storm:
  • Stay up-to-date with the latest weather information from MetService, Te Ratonga Tirorangi, New Zealand’s National Weather Service. Pay attention to heavy rain warnings. Short bursts of heavy rain may be particularly dangerous, especially after longer periods of wet weather.
  • Be especially alert when driving. Embankments along roadsides are particularly susceptible to landslides. Watch the road for collapsed areas, mud, fallen rocks, and other indications of a possible debris flow.
• Following a landslide, stay away from the landslide area. Further landslides may occur.

Types of Landslides and Their Processes

A landslide is the movement of rock, soil and/or vegetation, down a slope. There are many different types, and they can range in size from a single boulder in a rock fall, to a very large avalanche of debris with huge quantities of rock and soil that spreads across many kilometres. They are common in both rural and urban settings.

Landslides are commonly classified by the material involved (e.g., rock, debris, soil or mud) and the way they move (e.g., fall, topple, slide, spread, or flow). All these types of landslides may occur in New Zealand. Listed below are some classical examples of different landslide types.