5 things you should know about landslides
WASHINGTON (Sinclair Broadcast Group) – In California, rain and flash flooding caused devastating mudslides that killed at least 17 people. Five people remain missing.
More than 300 homes were damaged and more than 60 homes were destroyed.
When residents in the Montecito area were placed under mandatory and voluntary evacuation orders Jan. 9, many chose to stay in their homes. A decision that later turned fatal.
Here are five things you should know about landslides and how they occur.
What causes a landslide?
Landslides are when part of the ground breaks off due to erosion. The United States Geological Survey defines a landslide as “a wide range of ground movements, such as rock falls, deep failure of slopes, and shallow debris flows.”
That erosion can be caused by several factors such as heavy rain, wildfires, earthquakes, volcanic eruptions and weight from the accumulated from snow or rain. The flow of debris can be strong enough to move cars and homes, destroy property and obstruct modes of transportation.
All parts of the United States can become susceptible to landslides but areas on hill or slopes can experience them more frequently.
“Any area composed of very weak or fractured materials resting on a steep slope can and will likely experience landslides,” the USGS states.
Are landslides monitored?
Yes. Scientists with the USGS Landslide Hazards program partnered with other agencies to monitor landslides and learn more about their behavior. Understanding weather systems and their possible strength are important for predicting areas that could experience landslides.
Government agencies including USGS, National Oceanic and Atmospheric Administration (NOAA), National Weather Service Office of Hydrologic Development, Earth Systems Research Laboratory, and the National Severe Storms Laboratory, “developed a prototype debris flow warning system using weather forecasts and precipitation measurements along with regional USGS rainfall rate thresholds to determine the probability of debris flows,” according to NOAA.
These scientists place instruments into the ground and take periodic measurements. The instruments will then create data. These measurements are provided via “rain gauges, topographic data, soil moisture sensors, surface runoff sensors, and video cameras,” that information is then sent in real time to the forecasting offices at the National Weather Service.
After reviewing the information and data the NWS then decides on issuing a debris-flow warning.
The earlier scientists can detect the probability of a landslide, the faster people can be warned and evacuated. Currently, measurements are taken from USGS rain gauges,
“Plans for the warning system include new or improved ways to define how much rain various soil conditions can absorb before becoming unstable, estimates of when debris-flow may occur, and linking real-time monitoring of precipitation and hill slope conditions with advanced models” NOAA said on their website. “While the current system is designed to work in areas that have lost a lot of ground and tree cover to fire, the system could be expanded to include areas untouched by fire nationwide.”
How can wildfires lead to landslides?
In Dec. 2017, wildfires devastated southern California in many of the areas we are seeing landslides take place.
Wildfires damage not only trees but also the plants and soil on the ground. The soil after a wildfire does not absorb water as quickly. When heavy rains take place, water runoff can occur and lead to erosion. Areas like Santa Barbara and Ventura, where much of the hillsides were burned from fires, the risk of erosion and landslides dramatically increase.
The United States Geological Survey warns that the earth is more prone to landslides for two years after a wildfire event.
“In southern California, as little as 7 millimeters (0.3 inches) of rainfall in 30 minutes has triggered debris flows, and any storm that has intensities greater than about 10 millimeters/hour (0.4 inches/hour) is at risk of producing debris flows,” the USGS stated.
What safety steps can I take before a landslide?
If you can, sign up for mobile alerts on your cellphone and other mobile devices if you live in an area prone to landslides.
Landslides are likely to happen in areas where they have previously occurred. Watching where water runoff occurs on your property and avoid those areas during extreme weather and heavy rainfall. The USGS recommends having assessments of your property done for vulnerabilities and to research an area before you build or buy.
The Center for Disease Control and Prevention advise contacting your local authorities for evacuation routes and procedures.
What should you do during a landslide?
If a debris flow warning has been issued for your area, it is recommended that you stay on alert and awake. The USGS says that fatalities often occur when people are sleeping.
Listen for sounds that sounds like trees cracking and anything else that might suggest rushing water or moving debris. If you’re near a stream pay attention to changes in the water level, a decrease in water flow and color (murky or muddy) could indicate an oncoming landslide.
Watch for trees tilting or that may lean more severely.
If you’re trying to evacuate the area, do not cross flooding streams and avoid collapsed parts of the pavement. If you are able, get out of the direct path of the debris flow and protect your head from any falling debris.
Editor’s Note: Information about landslides was provided by the National Geological Survey, The National Oceanic & Atmospheric Administration Earth System Reacher Laboratory, Center for Disease Control and Prevention.