Lesson 3 | Geologic Processes and Hazards

Today, we'll be learning about landslides and what may cause them!

Landslide is an occurrence in which soil, rocks and vegetal debris are transported suddenly or slowly down a slope due to insufficient stability. It may happen when there is continuous rainfall, earthquakes and/or volcanic eruption accompanied by a very loud noise.

It can be a result of the failure of materials to make up the hill slope, and get driven by the force of gravity. Landslide is also known as landslips, slumps or slope failure.

Here is an example of a landslide, which was caused by human activities:

Courtesy of National Parks Service, United States of America

Causes of Landslide

Meanwhile, here are some human activities that may help speed up or trigger a landslide:

Courtesy of geoengineer.org

1.) Overloading Slopes

• When people build heavy buildings, houses, or dump soil on steep areas.
• Too much weight weakens the slope and causes collapse.
  Example: Houses built on mountainsides without proper support.

*Courtesy of: Mining for Zambia

2.) Mining Using Explosives

• Explosions underground shake and break rocks.
• This loosens soil and weakens the ground.
  Example: Blasting rocks for minerals, cement, or coal.

3.) Excavation or Displacment of Rocks

• Digging for roads, buildings, tunnels, or subdivisions.
• Removing supporting rocks makes slopes unstable.
  Example: Road widening on mountains.

4.) Changing Land Use (Construction on Slopes)

• Building roads, railways, buildings, and farms on hills.
• The natural shape of the slope is destroyed.
  Example: Cutting a mountain to make a flat road.

5.) Quarrying

• Digging, cutting, and blasting mountains to get gravel, sand, stones, and other materials.
• This removes large amounts of rock and soil.
  Example: Open-pit quarrying in hills.

6.) Land Pollution & Improper Land Use

• Mining and poor farming methods destroy soil.
• Polluted or loose soil cannot hold together.
  Example: Soil erosion from dirty mining.

7.) Excavation for Archaeology

• Digging out ancient objects or historical sites can weaken ground layers.
  Example: Exposed soil and rocks at excavation sites.

8.) Cutting Trees (Deforestation)

• Tree roots hold soil together.
• When trees are removed, the soil becomes loose and easily slides.
  Example: Illegal logging on mountains.

Landslides can cause property damage, injury and death and adversely affect a variety of resources. Water supplies, fisheries, sewage disposal systems, forests, dams and roadways can be affected for years after a slide event.

It can also affect daily life, as businesses can be stalled, and can also lead to injuries, or even death.

Are we prepared in case of landslides? These are some precautionary measures to observe and follow in preparing for landslides:

• Stay alert and awake. Many debris-flow fatalities occur when people are sleeping.
• If you are in areas susceptible to landslides and debris flows, consider leaving if it is safe to do so.
• Listen for any unusual sounds that might indicate moving debris, such as trees cracking or boulders knocking together.
• If you are near a stream or channel, be alert for any sudden increase or decrease in water flow and for a change from clear to muddy water.
  -Be especially alert when driving. Bridges may be washed out, and culverts overtop.
• Be aware that strong shaking from earthquakes can induce or intensify the effects of landslides.