What Causes a Landslide?


If you’re getting started on a building project, risk mitigation should be a top priority. One hazard that may be of primary concern is a landslide. Landslides can be incredibly devastating and are concerning due to their ability to take place almost anywhere. But, what is a landslide? According to the USGS, “a landslide is defined as the movement of a mass of rock, debris, or earth down a slope.”

Landslide is actually a somewhat broad term that encompasses five “mass wasting” modes, including falls, topples, slides, spreads, and flows. These movements are even further categorized based on geological material (bedrock, debris, or earth).

So, what causes a landslide? While gravity acting on an overly-steep slope is the primary culprit behind many landslides, there are other causes to be aware of:

  • Water-saturated slope materials through heavy rains or snowmelt
  • Erosion by rivers, glaciers, or ocean waves can lead to steep slopes
  • Earthquakes, especially of magnitude 4.0 or greater
  • Volcanic eruptions
  • Excess weight from snow and rain accumulation, stockpiling of materials, waste piles, or man-made structures

Now that you have some understanding of the causes of landslides, you may have other concerns like, “where do landslides occur?” You may also be interested in learning how to prevent landslides on the site of your next build. Our team has vast experience building commercial, residential, and public structures around the world, and can offer insight on how to mitigate risk involving landslides. Learn more about landslide risks and solutions below.

Where Do Landslides Occur?

As you gain an understanding of the risks and associated damage caused by landslides, it’s natural to wonder if your project is in a safe location. So, where do landslides occur? Unfortunately, the USGS reports that landslides can occur anywhere in the U.S. However, certain areas have a higher risk, including mountainous regions and large parts of Alaska and Hawaii. Essentially, any build site that has weak or fractured subsurface conditions is susceptible to a landslide.  You’ll want a respected geotechnical engineering group to help determine this—and how to design for these site conditions.

The good news is that most hazards can be mitigated in various project stages. From sound site investigation during the exploration phase, to implementing risk-reducing elements during the design process, and solid observation of recommendations during construction, you can minimize the risk that a landslide can have on your structure.

How to Prevent Landslides

Although they can occur anywhere, landslides don’t necessarily mean disaster for your project. After a thorough site investigation, you can develop a risk-management plan based on the findings. You can work with the unique conditions of your site to minimize hazards and damage caused by potential landslides. This is crucial, since landslides can be enormously costly and even deadly. After an investigation, your geotechnical engineer can help by providing recommendations on how to prevent landslides on your site with some of the following techniques:

  • Improving subsurface conditions: Soil compaction and the diversion of water from the site can help to minimize the risk of landslides. However, water must be diverted carefully so as to not create landslides in adjacent zones, and water should never be allowed to pond on a steep slope. “Off and away” is the adage geotechs use for this.
  • Constructing piles and retaining walls: Metal beams known as piles can be inserted deep into the bedrock to slow landslides. If there is a concern that landslides will maneuver through the piles, a retaining wall can be put in place. Retaining walls can be built with any number of materials and can be strengthened with tiebacks and buttresses.
  • Removal and replacement: Weak soil can be removed and replaced with materials more suitable to withstand landslides. Landslide prone materials should not just be simply pushed around the slope, as the risk will likely still remain.
  • Preserving vegetation: Vegetation can sometimes serve the role of metal piles, but in a natural way.  However, studies show that vegetative mitigation meant to help projects ends up hurting the stability instead.  This should be done very carefully.
  • Rock fall protection: Rock falls are designed to slow rogue boulders by building ditches, fences, and walls. Loose blocks that present a future fall risk can also be bolted into place to prevent a breakaway.

Once a landslide has occurred, there are also ways to minimize the damage. Excavating the rocks and soil at the head of a landslide can mitigate damage. Also, buttressing the toe of the landslide can prevent further sliding if the buttress is placed properly.

Slide risk is a very complicated subject that should only be addressed with a good geotechnical engineering group at your side.  Each site is unique, and if the risk is determined to be high, each site may require site-specific investigation requirements, as well as mitigation measures designed by a geotech and structural engineer.

Work With Central Geotechnical Services On Your Project

If landslide damage is a concern at your job site, consult with Central Geotech. We have encountered a tremendous variety of risks in projects undertaken in diverse regions, and we can help you craft a mitigation plan. Feel free to get in touch with our team to discuss the issues present at your project, or to talk shop on any upcoming jobs. We look forward to collaborating with you on a successful build soon!