Mudslides are a fast-moving landslides caused by disturbances in the natural stability of a slope. They can happen after heavy rains, droughts and earthquakes.
With the most powerful storm of the season thrashing the Los Angeles area over the next few days, people are fearing dangerous conditions, property damage and for their safety.
Following a five year drought, Californians are now facing challenges with severe storms plaguing the state. It will take years for the state’s overburdened groundwater reserves to recharge but the surface is another issue. California’s blessing and curse right now is the torrential recurring downpours. Atmospheric rivers are picking up moisture over the Pacific Ocean and carrying it north, dumping copious amounts along the way. Usually, in a good year, there’s one atmospheric river. This year, they are coming back to back to back. Though the recent rains have caused serious problems throughout Northern California, the threat grows for Southern California as well.
Mudslides generally develop when water rapidly accumulates in the ground resulting in a surge of water-saturated rock, earth, and debris. Mudflows occur most in mountainous places where a long dry season is followed by heavy rains.
On steep hillsides, debris flows begin as shallow landslides that liquefy and accelerate. A typical landslide travels at 10 miler per hour, but can exceed 35 miles per hour. Slides can occur in all 50 states, but regions like the Appalachian Mountains, the Rocky Mountains and the Pacific Coastal Ranges have “severe landslide problems,” according to the USGS. The agency lists California, Oregon, Washington, Alaska and Hawaii as especially prone.
What areas are at risk?
- Areas where wildfires or construction have destroyed vegetation.
- Areas where landslides have occurred before.
- Steep slopes and areas at the bottom of slopes or canyons.
- Slopes that have been altered for construction of buildings and roads.
- Channels along a stream or river.
- Areas where surface runoff is directed.
How to prepare:
- Develop emergency and evacuation plans for your family and business.
- If you live in an area vulnerable to landslides, consider evacuation. Contact local authorities about emergency and evacuation plans.
- Have a fully stocked first aid kit, alternative lighting (avoid flammable lighting such as candles or lanterns), a portable radio with extra batteries, and a strong food and water supply if you intend to stay in a dangerous area.
- Be sure family, friends and co-workers are aware of your intent to stay and your exact location in advance of threatening weather (in the event you are in danger and unable to contact anyone later).
- Listen to the radio or watch TV for warnings about intense rainfall or for information and instructions from local officials.
What to do during intense storms:
- Continue to following reports on the radio or TV for updates or for information and instructions from local officials.
- Be aware of any sudden increase or decrease in water level on a stream or creek that might indicate debris flow upstream. A trickle of flowing mud may precede a larger flow.
- Look for tilted trees, telephone poles, fences or walls, and for new holes or bare spots on hillsides.
- Listen for rumbling sounds that might indicate an approaching landslide or mudslide.
- Be alert when driving. Roads may become blocked or closed due to collapsed pavement or debris.
- If you see a landslide or mudslide starting, quickly move away from the path of the slide. Getting out of the path of a mudslide is your best protection. Move to the nearest high ground in a direction away from the path. If rocks and debris are approaching, run for the nearest shelter and take cover under a desk, table or other piece of sturdy furniture. (We recommend the same actions as if you were in an earthquake as described in our Earthquake Safety Blog.)
What should you do following a landslide:
- Stay away from the site. (Flooding or additional slides may occur after a landslide or mudslide.)
- Continue to listen to the radio or TV for emergency information.
- Report broken utility lines to the appropriate authorities.
- Consult a geotechnical expert for advice on reducing additional landslide problems and risks. Local authorities should be able to tell you how to contact a geotechnical expert.
- Again, we recommend you use the same precautions following a landslide that you would after an earthquake.
IF YOUR HOME OR BUSINESS WAS IN OR NEAR A LANDSLIDE
- Please remember that even if the structure may appear safe but shifted, it is NOT safe.
- Have a professional contractor or engineer inspect the structure for; electrical system damage, damage to gas lines or leaking gas and damage to water or sewer lines.
- Remember, even if your structure is not visibly damaged but their was a landslide in the immediate area, there are still concerns such as contaminated water or a weakened foundation.
With the threat of mudslides growing during these unusually heavy and repetitious downpours, we hope that you can stay safe. Please also remember, when driving in severe rain storms to practice safe driving procedures for inclement weather.