Landslide Threats in Southern California

Southern California has many areas that are susceptible to landslides in many forms. The past couple of weeks have demonstrated that these slides can have dramatic affects on the regions infrastructure. While most slides aren’t that preventable, the damage they can create can be mitigated.

Understanding the signs of a pending landslide are fairly easy and should not be ignored. If you live in an area where landslides are possible, look for these signs:

  • Ground cracks, particularly ones that appear to pull apart
  • Sinking areas or changes in ground level
  • Unexplained leaks in pipes
  • Tilting poles
  • New cracks appearing in a structure
  • New springs or areas where water seems to drain without appearing on the surface

These signs are important to look out for. The first one, ground cracks, are the most obvious. They tend to arcuate and numerous. The largest ones may mark the head of the slide, though that is not a precise indicator of how large a slide may become. Ground cover itself doesn’t prevent deep seated landslides but it can help with smaller surficial slope failures. If you see any of these signs, please contact an engineering geologist or other local official to help assess the likelihood of a failure. Doing so can help prevent injury, loss of life, and property damage.

Mudslides, such as those that recently blocked Interstate 5 in Grapevine Canyon and State Route 58 in Cache Creek Canyon, are more common on steeper slopes with loose material. These tend to happen more commonly in areas which have burned recently, leaving little plant material and a soil that is less porous than it was previously. Those conditions, combined with a heavy rainfall, can turn that material into a thick mud which can easily move larger objects, such as boulders and trucks. As such, these slides can be very dangerous and fast moving.

The California Geological Survey has put together a series of maps to help determine the likelihood of a slope failure. These maps cover most of the metropolitan regions of California and are a great resource. They should, however, only be used as a guideline for potential slope failures. A more exact analysis should be determined through a geological report on your specific location.

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