A Closer Look at Landslide Prevention
By Jane Marsh
Few natural events invoke as much fear as the earth giving out underneath you. A landslide occurs when a large section of rock, snow, mud or soil slides down a slope. Unlike tornadoes, droughts or thunderstorms, however, this type of natural disaster is often easily preventable. Here’s how being landslide-smart saves lives.
Understanding What Causes Landslides
Most landslides occur in hilly regions. They’re frequently triggered by flash floods or earthquakes that destabilize the ground. When a landslide occurs, the material on a slope moves or breaks apart, causing it to collapse as gravity pulls it downward.
Although landslides do occur naturally, climate change is causing them to become more frequent. At the same time that many areas are getting less rainfall, storms have become more intense, leading to worse erosion. The movement of soil makes the ground less stable.
Human development is also a contributing factor to landslides. Altering natural drainage systems, mining, building roads without adequate grading and cutting down trees — whose roots hold down the soil and absorb floodwater — can all lead to more severe landslides. What can we do to prevent these disasters?
Date: 23 October 2011
Credit: Mti
Building in the Right Place
Some areas are more prone to landslides than others. As the global population increases, many people have begun constructing homes near mountain edges, slopes, erosion valleys or drainage ways because they can’t find a better spot. Some people even build in areas where landslides have already occurred.
However, these areas are geologically unstable. Avoiding building in these zones is a good first step toward preventing landslide damage. The safest areas to build are flat land far from slopes, at or along the tops of ridges, and on hard, solid bedrock that has never moved before.
Additionally, properties that experience low rainfall intensity and shorter periods of rain are less susceptible to landslides. Good drainage systems can also protect homes from sliding downward during a storm.
Assessing Risk
Before constructing a new home, it’s important to conduct an official site analysis of the property.
Engineering firms and geologists can offer important insights about a property’s landslide risk. They look for hints of previous landslide damage, such as tilted trees or cracked pavement. They may examine the ground for evidence of erosion or unstable soil. If they discover these signs, they usually advise people to build their home elsewhere.
Has the area experienced landslides before? If so, that’s a sign another landslide will likely occur in the future.
Engineering to Prevent Landslides
Sometimes, building in a landslide-prone area is unavoidable. In that case, engineers and city planners use several techniques to stabilize the ground, including:
Erosion — soil blowing away — is a major cause of landslides. Mulch material, including compost, wood, gravel and straw, can be added on top of loose soil to help pack it down. As a bonus, mulch often encourages plants to grow, allowing their roots to hold down the soil even further.
Have you ever noticed a roadside slope covered in netting or with a large retaining wall in front of it? These techniques prevent rocks, dirt and other debris from sliding down into the road. Other slope stabilization methods include driving soil nails or rock bolts into the ground, building crib walls and planting deep-rooted vegetation along the slope.
If water builds up along a slope, it can wash the soil away or push it down under its weight. Engineers install pipes and dig drainage ditches to alleviate pressure and direct water where it needs to go.
Cutting or building up a slope to the desired angle — a process known as grading — also helps water flow off and prevents erosion. Reducing the steepness of the slope decreases the gravitational forces acting on it, making it less susceptible to landslides.
Terracing means building flat areas along steep slopes. This technique reduces a slope’s angle, redistributing mass along the slope. Terrace farming, for example, involves planting crops in level areas along a hillside, helping conserve water and prevent erosion.
Educating the Public
Governments should ensure people are aware of landslide risks so they don’t try to build in unsuitable areas. Educational campaigns can also teach people what a landslide looks like, helping them quickly report it to authorities.
In Malaysia, for example, a public awareness campaign called “Learn, Maintain, Monitor and Report” taught the public about the types of landslides, what triggers them and how engineering can prevent them. Officials also encouraged people to recognize and report the signs of an impending landslide.
As a result, community members became more aware of landslide behavior. Local authorities even requested further training to learn more about slope management and landslide prevention.
Landslide Warning Signs
How do you know when a landslide is occurring or will likely happen soon? Look for these common signs:
- The ground bulging near the base of a slope
- Stairs or walls pulling away from a building
- Underground gas and electric lines breaking
- Tree trunks snapping or boulders knocking together
- Pavement cracking
- Streams or puddles springing up in new locations
- Windows or doors becoming jammed unexpectedly
- Landscape changes such as leaning trees or ground movement
What to Do During a Landslide
If you think a landslide is about to happen, evacuate if it’s safe to do so. Remember not to cross flooding streams. If you’re driving, look for signs of debris flows such as mud, fallen rocks or collapsed pavement and stay away from these areas.
Call your local police or fire department to inform them of what’s happening. It’s a good idea to call your neighbors, too, because the landslide could affect their homes.
If you can’t leave your house, go upstairs if possible — the first floor may become flooded with debris. Curl up into a ball and protect your head.
After a landslide, report any damaged roads or utility lines to the authorities. Keep your distance from the landslide area and stay alert, since floods often follow landslides.
Landslide Prevention: Staying One Step Ahead
Human activity and climate change are worsening the effects of natural disasters. However, thanks to advances in engineering and a better understanding of geology, landslides are more preventable than ever. By knowing where to build, how to control erosion and what to do if an emergency occurs, we can protect people and property against landslides, leaving the world a more stable place.