Land shape (geomorphology) and composition (geology) are the main factors that contribute to land instability. In Auckland, landslides and soil erosion occur in soft, weak soils that have been weathered over many thousands of years.
Land instability examples
Common examples of land instability in Auckland include:
- landsliding (mass movement downslope of material under the influence of gravity), including: rotational slides, translational slides, slumps, flows, falls
- subsidence (can occur on flat land as well as sloping, usually the result of draining or overloading weak soils)
- tunnel gully erosion (tunnels form below the slope surface and eventually collapse)
- stream and river bank erosion
- coastal erosion
- topsoil erosion.
Impacts of land instability
Some potential impacts on property and people in Auckland include:
- danger to life in the case of sudden landslides
- damage or destruction of buildings and impacts on lifeline infrastructure
- loss of land, particularly in coastal cliff environments
- destabilisation of neighbouring slopesand properties
- environmental impacts of sedimentation in waterways
- secondary hazards such as leaking gas or water from broken pipes.
Monitoring land instability hazards
GNS Science, through the GeoNet Project, manages the New Zealand Landslide database, which includes the date, location, size and damage of significant landslides, as well as a list of all known landslides. It has a collection of landslide-related data resources and tools.
Visit the New Zealand Landslide database on the GeoNet website.