What is a landslide?
A landslide is a movement of rock, debris or earth down a slope. Landslides result from the failure in the structure of the materials which make up the hill slope and are driven by the force of gravity. Landslides can also occur underwater. These underwater landslides, or onshore landslides that slump into the ocean, can potentially cause tsunami.
Onshore landslides in Australia have caused fatalities, environmental degradation and millions of dollars of damage to buildings, roads, railways, pipelines, communication networks and agricultural land.
How do landslides move?
The movement of landslide material can vary from abrupt collapses to slow gradual slides and at rates which range from almost undetectable to extremely rapid. Sudden and rapid events are the most dangerous because of a lack of warning and the speed at which material can travel down the slope as well as the force of its resulting impact. Extremely slow landslides might move only millimetres or centimetres a year and can be active over many years. Although this type of landslide is not a threat to people they can cause considerable damage to property.
Landslides range in size from a single boulder in a rock fall or topple, to tens of millions of cubic metres of material in a debris flow. They can also vary in their extent, with some occurring very locally and impacting a very small area or hill slope while others affect much larger regional areas. The distance travelled by landslide material can also differ significantly with slides travelling from a few centimetres to many kilometres depending on the volume of material, water content and gradient of the slope.
What causes landslides?
Landslides can be triggered by natural causes or by human activity. In general, the factors which influence whether a landslide will occur typically include slope angle, climate, weathering, water content, vegetation, geology, slope stability and the amount of loading on the slope (overloading).
How these factors interrelate is important in understanding what causes landslides along with an understanding of the impact humans have on these factors by altering natural processes.
Typically, a number of elements will contribute to a landslide, but often there is one which triggers the movement of material.
Natural causes include:
- elevation of pore water pressure by saturation of slope material from either intense or prolonged rainfall and seepage
- vibrations caused by earthquakes
- undercutting of cliffs and banks by waves or river erosion
- volcanic eruptions.
Human causes include:
- removal of vegetation
- interference with, or changes to, natural drainage
- leaking pipes such as water and sewer reticulation
- modification of slopes by construction of roads, railways, buildings, etc.
- overloading of slopes by construction of buildings or earthworks etc.
- vibrations from heavy traffic, blasting, etc.
- excavation or displacement of material, including mining and quarrying activities.
It is important for engineers and geologists to evaluate slope stability and any landslide threat during development assessments so that effective and timely preventative and/or remedial measures can be implemented.
Where do landslides occur in Australia?
Landslides occur in every Australian state and territory. They can occur in many different types of landscapes, but are mostly likely in areas with high rainfall, cliffs and steep slopes and/or unstable rock types.
Landslide prone regions in Australia include:
- Great Dividing Range, or the Eastern Highlands
- Great Escarpment running east of the Great Dividing Range along most of the east coast
- Strzelecki and Otway Ranges in southern Victoria
- Mt Lofty Ranges near Adelaide in South Australia
- Blue Mountains in New South Wales
- Mt Wellington, Tamar Valley and north-west coast of Tasmania.
Some of the most common types of landslide in Australia are earth slides, rock falls and debris flows.
Report a landslide
If you would like to report a landslide please email firstname.lastname@example.org. Please include as much detail about the landslide as you can, such as:
- where it occurred
- when it occurred
- the movement type and rate
- the cause and impact.
Photos and references are also welcome. Please include your contact details, so that we can get in touch with you if we need more information.
- Since 1842, there have been around 1600 recorded landslide events which have resulted in damage to roughly 2500 buildings and the destruction of approximately 400, as well as the death of around 200 people and injury to approximately 400 (National Landslide Database, 2016).