Southern California can’t catch a break. Enjoy a sunny climate, get wildfires. Wish for rain, get mudslides.
After record-setting wildfires that lasted all the way to late December, the first rain in Southern California in months caused a major mudslide that killed more than 15 people, injured others, and destroyed several dozen homes. Rescue teams are still searching for survivors in the wreckage.
I probably should write more about landslide events. We live part-time in Gatlinburg, Tennessee, with a mountain home overlooking town and the Great Smoky Mountains National Park. As such, we live on a slope. How much of a slope? Let’s just say you wouldn’t want to take a dive off our deck.
A mudslide, sometimes called a “debris flow”, is a landslide with a high water content. Mudslides act like a river that, if the mud is thick, has the consistency of wet concrete. Mud, rocks, trees, and other large objects are carried along and can cause homes to collapse and a huge amount of traumatic injury to residents.
Another type of landslide is a “mud flow“, which is characterized by a very rapid flow of water and debris. A mud flow is more “liquefied” due, at least partially, to a lot of rain in a short period of time. A third of the rainfall in Southern California when the rains finally came occurred in five (yes, five) minutes.
In the U.S., 25-50 deaths occur on average as a result of landslides.
Mudslides occur for a number of reasons: Periods of heavy rainfall or snow melt saturate the ground and cause instability in sloping areas. Areas prone to earthquakes, hurricanes, wildfires, and other natural disasters are especially susceptible. In the case of the California mudslide, soil which had been charred by recent fires made the it less absorptive; as such, water that couldn’t get through hard earth quickly formed a flash flood that cascaded down slopes, picking up soil and debris to become a mudslide.
CAN YOU PREVENT A MUDSLIDE?
Humans contribute to the risk of mudslides by planning poorly: Roads cut into hills and mountains and scenic mountain homes make mudslides more likely. River retreats at the base of a hill or mountain (in the “holler”, as we say in Tennessee) are also vulnerable.
Once you’ve built that home on a hillside, there’s a limited amount of preventative measures that can be undertaken. It’s a different story, however, when planning out that dream home:
-Beware of steep slopes, natural or man-made runoff conduits, or eroded areas.
-Have the county Geological Survey specialist assess your property for possible mudslide risk.
-Consider flexible pipe fittings (installed by pros) less prone to gas or water leaks.
-Consider building a retaining wall in likely mudslide channels.
-Avoid areas that have experienced mudslides in the past.
-Plan out an evacuation route.
-Have a battery-powered NOAA weather radio.
-Have a medical kit with items to deal with both traumatic injury and water sterilization.
WARNING SIGNS OF A HOME AT RISK
Sometimes, pressure from unstable earth may give you a hint that trouble is on the way and give you time to evacuate. Mudslide prone areas will begin to show signs of strain:
-Cracks develop in walls, flooring, paving, driveways, or foundations.
-Outside structures (for example, stairs) begin to separate from buildings
-Doors and windows start becoming jammed.
-Utility lines start breaking.
-Fences, trees, and utility poles start tilting.
-Water starts accumulating in strange places
-Roads and embankments along slopes start breaking off at the edges.
-The Terrain starts to “bulge” or starts slanting at the base of the slope.
DURING THE EVENT
-Turn on the NOAA radio and listen to warnings as they are reported.
-Warn your neighbors!
-If a mudslide is imminent, get out of Dodge if at all possible, with the understanding that roads may be washed out. Stay away from mudslide areas; new mudslides may still occur.
In some mudslides, as in Southern California, things happen very quickly and you don’t have time to evacuate:
-If you stay home, get to the second story if you have one.
-Watch for and avoid downed power lines.
-As the slide passes through, get under a table and curl into a ball, protecting your head.
-If you’re trapped in the mud, survival rates go up if you can form an air pocket around you.
-it’s a good idea to carry a cell phone with you at all times in case you are trapped in the house.
Mudslides, like wildfires, leave scars on the land but are part and parcel of living with Mother Nature. Plan before you build, know the danger signs, and hit the road if at all possible in the face of an imminent threat.
Joe Alton MD
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