Landslides can be caused by many factors including earthquakes, storms and human modification of land. The most deadly landslides are the ones that occur quickly, like debris flows, often with little notice. Whether you are at home or out for a drive, the best way to prepare is to stay informed, and understand when a dangerous landslide is likely to occur.
In a landslide, masses of rock, earth or debris move down a slope. Debris and mud flows are rivers of rock, earth, and other debris saturated with water.
Although some landslides require lengthy rain and saturated slopes, a debris flow can start on a dry slope after only a few minutes of intense rain. “Intense” rain means a burst of rain at a fast rate, about half an inch in an hour. With debris flows, the rate matters more than total rainfall.
Before a Landslide
The following are things you can do to protect yourself, your family and your property from the effects of a landslide or debris flow:
- Prepare for landslides by following proper land-use procedures - avoid building near steep slopes, close to hill edges, near drainage ways or along natural erosion valleys.
- Become familiar with the land around you. Learn whether landslides have occurred in your area. However, don’t assume that what happened last time will happen next time. Debris flows can start in places they’ve never been and return to slopes where they’ve already been.
- Get an assessment of your property by a qualified professional.
- Consult a professional for advice on appropriate preventative measures for your home or business, such as flexible pipe fittings, which can better resist breakage.
- In mud and debris flow areas, consider building channels or deflection walls to try to direct the flow around buildings. Be aware, however, that when a flow is big enough, it goes where it pleases.
Recognize Warning Signs
Watch for debris flows and other fast moving landslides that pose threats to life:
- Listen and watch for rushing water, mud, unusual sounds.
- Unusual sounds, such as trees cracking or boulders knocking together, might indicate moving debris.
- A faint rumbling sound that increases in volume is noticeable as the landslide nears.
- Fences, retaining walls, utility poles, k-rails, boulders, or trees move.
- Huge boulders in the landscape can be signs of past debris flows.
Watch for slow-moving landslides that pose threats to property:
- Changes occur in your landscape such as patterns of storm-water drainage on slopes (especially the places where runoff water converges) land movement, small slides, flows, or progressively leaning trees.
- Doors or windows stick or jam for the first time.
- New cracks appear in plaster, tile, brick, 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.
- The ground slopes downward in one direction and may begin shifting in that direction under your feet.
During a Landslide
- During a storm that could cause a landslide, stay alert and awake. Many deaths from landslides occur while people are sleeping.
- Be aware that by the time you are sure a debris flow is coming, that will be too late to get away safely. Never cross a road with water or mud flowing. Never cross a bridge if you see a flow approaching. It can grow faster and larger too quickly for you to escape.
- If you do get stuck in the path of a landslide move uphill as quickly as possible.
After a Landslide
- Stay away from the slide area. There may be danger of additional slides.
- Listen to local radio or television stations for the latest emergency information.
- Watch for flooding. Floods sometimes follow landslides and debris flows because they may both be started by the same conditions.
- Check for injured and trapped persons near the slide, without entering the direct slide area.