Some landslides move slowly and cause damage gradually, others move so rapidly that they can destroy property and take lives suddenly and unexpectedly. Gravity is the force driving landslide movement. Factors that allow the force of gravity to overcome the resistance of earth material to landslide movement include saturation by water, steepening of slopes by erosion or construction and earthquake shaking.
Landslides are typically associated with periods of heavy rainfall and tend to worsen the effects of flooding that often accompany these events. In areas burned by bushfire a lower threshold of rainfall may initiate landslides.
Debris flows, sometimes referred to as mudslides, are common types of fast moving landslides. These flows generally occur during periods of intense rainfall. They usually start on steep hillsides as shallow landslides that liquefy and accelerate to speeds that are typically about 16kph, but can exceed 50kph. The consistency of debris flows ranges from watery mud to thick, rocky mud that can carry large items such as bounders, trees and cars. Debris flows from many different sources can combine in channels, and their destructive power may be greatly increased. They continue flowing down hills and through channels, growing in volume with the addition of water, sand, mud, boulders, trees and other materials. When the flows reach flatter ground, the debris spreads over a broad area, sometimes accumulating in thick deposits that can wreak havoc in developed areas.
- Learn about the landslide risk in your area.
- Develop an evacuation plan that details which route you will use to escape a landslide and an alternative if your main route is blocked.
- Discuss landslides and debris flow with your family.
- If your property is in a landslide risk area, contact a company specialising in geotechnical engineering, civil engineering or structural engineering for advice on corrective and protective measures you can take.
- Become familiar with the land any structures around you so that you will notice any changes.
- Watch the patterns of storm water drainage on slopes near your home, and especially the places where runoff water converges, increasing flow over soil covered slopes.
- Plant ground cover and build retaining walls to limit the chances of a landslide occurring.
Landslide Warning Signs
- Doors or windows stick or jam for the first time.
- New cracks appear in plaster, tiles, bricks or foundations.
- Outside walls, walks or stairs begin pulling away from the building.
- Slowly developing, widening cracks appear on the ground or on paved areas such as streets or driveways.
- Underground utility lines break.
- Bulging ground appears at the base of a slope.
- Water breaks through the ground surface in new locations.
- Fences, retaining walls, utility poles or trees tilt or move.
- You hear a faint rumbling sound that increases in volume as the landslide nears. The ground slopes downward in one specific direction and may begin shifting in that direction under your feet.
If you Suspect an Imminent Landslide Danger
- If you believe there is a real potential for a landslide to occur within a short period of time call the emergency services immediately on 000. If you are unsure or there are no indicators of an immediate threat contact Council immediately.
- Inform affected neighbours. Your neighbours may not be aware of potential hazards. Advising them of a potential threat may help save lives. Help neighbours who may need assistance to evacuate.
- Evacuate. Getting out of the path of a landslide or debris flow is your best protection.
What to do During a Landslide
- Quickly move out of the path of the landslide or debris flow. Moving away from the path of the flow to a stable area will reduce your risk.
- If escape is not possible, curl into a tight ball and protect your head. A tight ball will provide the best protection for your body.
What to do After the Landslide
- Stay away from the slide area. There may be a danger of additional slides.
- Check for injured and trapped persons near the slide, without entering the direct slide area. Direct rescuers to their location.
- Help neighbours who may require special assistance. Elderly people and people with disabilities may require additional assistance. People who care for them or who have large families may need additional assistance in emergency situations.
- Listen to local radio or television stations for the latest emergency information.
- Watch for flooding, which may occur after a landslide or debris flow. Floods sometimes follow landslides and debris flows because they may both be started by the same event.
- Look for and report broken utility lines to appropriate authorities. Reporting potential hazards will get the utilities turned off as quickly as possible, preventing further hazard and injury.
- Check the building foundations and surrounding land for damage. Damage to foundations and the surrounding land may help you to assess the safety of the area.
- Replant damaged ground as soon as possible since erosion caused by loss of ground cover can lead to flash flooding.
- Seek the advice of a geotechnical expert for evaluating landslide hazards or designing corrective techniques to reduce landslide risk. A professional will be able to advise you of the best ways to prevent or reduce landslide risk, without creating further hazards.