Landslides

Printer-friendly version
Listen: 

Landslides are a natural process that removes material from hills, mountains and coastlines. Landslides are common in New Zealand and can range from small events to damaging large scale events.

Unstable land

Compared to many other countries, New Zealand has a high number of landslides because:

  • land is still being uplifted
  • rocks are often weakened by geological folding and faulting
  • there are frequent earthquakes
  • much of the land is hill country, formed by rivers cutting into soft clay rocks
  • slopes can be unstable, weak layers of volcanic ash or loess
  • rainfall can be high.

Some landslides move whole mountain sides, taking millions of cubic metres of material, at up to 200 kilometres per hour. Others are shallow or slow, moving only a few centimetres a year.

Causes

On unstable slopes, three things are important in producing large landslides:

  1. land conditions, such as weak rock and steep slopes
  2. processes which further weaken the slope, such as deforestation or undercutting by streams
  3. triggering factors such as intense rainstorms (100 millimetres or more in 24 hours) and large earthquakes (magnitude 7 or greater)

Human impact

Deforestation has had the largest impact on the stability of hillsides. Clearing land for farming has increased landslide activity by about seven times its natural rate. Road construction and subdivision earthworks can also destabilise slopes and increase landslide rates. 

Cost

Each year local councils, roading authorities, private landowners and railway operators spend millions of dollars clearing slips from roads and railway lines. It is a never-ending task – there are always more floods or earthquakes to come, and there is plenty of rock and soil waiting to tumble down.

In general, landslides are more common in New Zealand than many other countries because of the terrain and less stable conditions. However, landslides cause few deaths in New Zealand because there are few settlements in mountainous areas and the population density is relatively low.

Before

  • Find out if there have been landslides in your area before and where they might happen again.
  • Check for signs that the ground may be moving. 
  • Watch the roadside for collapsed pavements, mud and fallen rocks.

During

  • Act quickly - getting out of the path of a landslide is your best protection.
  • Evacuate straight away. Take getaway items with you and your pets if you can safely do so.
  • Warn neighbours who might be affected and help those you are able to.
  • Contact emergency services and your local council to tell them of the hazard.

After

  • Do not return to the area until you are told it is safe.
  • Avoid dangling and broken power lines.

 

 

 

 

 

 

 

 

 

Ready for a quiz?

Audio Maori keywords: 


  • Samoan keywords

  • Tongan keywords

  • Cook Islands Māori keywords

  • Niuean keywords


You could find out if and where there has been a landslide in your local area and what caused it.

Previous
Floods

Next
Storms

Easy

A massive rock avalanche changed the height of New Zealand's highest mountain, Aoraki Mount Cook, in December 1991. Can you find out about other large rock avalanches in New Zealand? Image: Loyd Homer, GNS Science.

Landslides are common in New Zealand. This landslide is in Whakatāne. Can you find out what large landslides there have been in New Zealand recently. Image: LEARNZ.

One of New Zealand's most well known landslides was the 1979 Abbotsford landslide in Dunedin which left 69 houses uninhabitable. What type of landslide was this and was anyone hurt? Image: GNS Science.

Landslides are common in areas that have been cleared of trees for farmland, especially after heavy rain. Image: LEARNZ.

There are different types of landslides. Sometimes landslides can be a combination of different types. I wonder what are the most common landslides in New Zealand? Image: United States Geological Survey. Art work by Margot Johnson.