A landslide is the movement of a mass of rock, debris, or earth down a slope. Sometimes this can be a slow process taking months or years and primarily pose a risk to property and the environment. However, landslides pose a significant risk to the safety of people, especially if they happen quickly.
Landslides can occur by natural processes but can also be caused or exacerbated by human activity. This makes them difficult to predict and a complex problem to deal with.
Some of the common natural factors which contribute to landslides include:
- Geology (including the thickness and type of soil overlying bedrock)
- The slope (steepness) of the land
- Aspect (direction the slope faces)
- Depth of the water table or perched water tables
- Poor drainage of soils
- Soil erosion lost through rain/wind
- Weather events such as intense storms/floods or bushfires and climatic conditions such as drought and rising sea levels.
Some of the common human induced factors that contribute to landslides include:
- Buildings and earthworks (including excavation or filling of land and inappropriate design or response to the site conditions)
- Vegetation removal
- Poor drainage of soils or concentration of water as a result of works
- Soil erosion lost through repeated movement of people, animals and vehicles
Some factors which can trigger a landslide include:
- Heavy or prolonged rainfall (including from major storms)
- Flooding, and
- Earthquakes
Landslides are generally more likely to occur where soils are thicker, slope angles are steeper, or the amount of water in the ground is higher. Therefore, the more we can preserve the natural landform, vegetation and drainage, the less susceptible slopes will be to landslide.