Landslides that forced authorities to cut off electricity and gas to hundreds of homes Palos Verdes Ranch over the past two months highlight the risk of living on land that could shift and erode without notice.
Deep landslides can occur weeks or months after heavy rains, when water has time to seep into weak rock areas, creating a landslide plane under the weight of the rock and of the overlying soil, according to the report. California Geological Survey.
These types of landslides generally occur on moderately steep slopes.
If you’re in the market for a home, experts say there are several ways to determine if you’re buying a property with a high risk of landslides.
What causes landslides
Landslides are part of the natural process that erodes mountains and moves sediment to the ocean through river systems. “It’s important to the basic process of erosion,” said Jonathan Godt, landslide hazard program coordinator for the United States Geological Survey.
“Over the course of human life, we are just a blink of an eye in geologic time, so (landslide) issues or these processes don’t enter our consciousness until something like the unfortunate situation of Palos Verdes Ranch it happens,” he said.
In 2011, the The California Geological Survey created a map this shows that a majority of the state’s coastline is at risk of landslides.
Homes built decades ago on old landslides that were once inactive are “OK for a while, (but) sometimes there are changes,” Godt said.
Several factors can change the active state of a landslide, such as rainfall and earthquakes, but the warning signs are difficult to see because they are “well beneath our feet and sort of hidden,” he said. he declared.
When properties located in these areas are for sale, it is up to buyers to assess the risk of land movement of the property they are interested in.
If the seller or his agent knows that the property is located in a seismic risk zone subject to strong ground shaking, soil liquefaction or landslide, information must be disclosedaccording to the state Department of Real Estate.
But buyers are also responsible for conducting their own research.
Researching a Property’s Landslide Risk Online
At least two websites, Realtor.com And Redfin.com, provide information on the natural disaster risk of the property. At the bottom of the listing, you’ll find a section that details the property’s flood, fire, heat, wind and air hazards. Unfortunately, landslides and ground movements are not disclosed factors.
Instead, potential buyers should do a Google search of the neighborhood next to the words “landslide” or “natural disaster.” If there have been landslides in the past, news reports about these issues will likely surface, said Timothy D. Starkprofessor of civil and environmental engineering at the University of Illinois.
For more scientific data, buyers can turn to three landslide maps created by the California Geological Survey. THE Database of reported landslides has reports of landslides from local governments, the National Weather Service and citizen scientists. THE Landslide index allows users to request reports and other documents on landslides in a specific area. THE California Deep Landslide Susceptibility and Landslide Inventory includes a map of the state that marks landslide risk areas in dark red.
The California Department of Conservation also released a California Landslide Response Report 2023 which included a page showing where deep landslides could occur after 2023 storms.
Stark also suggested using Google Earth Pro to examine aerial images over time to detect ground movement.
When you search for an address or neighborhood on Google Earth Pro, it will automatically show you the current image. To view past frames, click the View tab, then Historical Frames or click a small clock icon above the 3D viewer. You can then zoom in or out to change the start and end dates.
When looking at the surface of the area you’re looking for, Stark said to look for features in the ground surface such as drops in nearby hillsides or reddish areas (that have exposed or no vegetation) that indicate steep slopes – all potential signs of a previous slope. movement.
Looking for signs of past or potential landslide activity
Other signs of landslide risk can be spotted with the naked eye when viewing a property you wish to purchase.
When you visit the neighborhood, take a look at the surrounding properties.
If the house is located near or around hills, examine the hill or slope itself. A sign of land movement is if the ridge at the top of the hill is flat and then has a steep curve, slope or cracks, suggesting a previous landslide.
Check the base of the hill; if the ground is lifted, it is a sign of movement.
Consider how close the hill or slope is to the property you are interested in. If there is a sudden ground movement or landslide, the higher the nearby hillside, the farther a landslide can travel, Stark said.
Other signs of past land movements in the region could include:
- Misaligned fence, sidewalk, guardrail, utility poles, trees or walls.
- Cracks visible on the ground.
- Above ground water and sewer pipes.
- Cracked or deformed pavement.
- Shift the yellow or white lines on the roadway.
- Neighborhood houses supported by wooden planks or railway ties.
- Cracked or leaning houses.
You can also check if the ground is moving by taking a photograph of the shifted lines on the ground or a crack in the pavement and returning to the same site a week or two later to see if there is a visible difference, a Stark said.
If you decide to make an offer on a home and begin escrow, a home inspector can help you determine if any past land movement has affected the property.
Stark said home inspectors will conduct an assessment of the home and examine the walls, drywall and foundation for any type of cracks that suggest ground movement. Inspectors will also check if the walls are straight and if the floor inside the house is level.
Inspectors can also suggest whether a geotechnical engineer is needed to take soil samples of the home. These tests make it possible to detect the behavior of the soil under various conditions.
Insurance against landslides?
Natural disasters such as earthquakes, floods and landslides are generally not covered by a general home insurance policy.
However, homeowners can purchase a non-standard insurance policy, called a difference in condition policy, which is often used to cover damage caused by earthquakes.
Jerry Becerra, president of Heffernan Barbary Insurance Services, said it is possible to find a DIC policy covering earthquakes where the definition of earth movement is broad enough to include landslides. But he added that such a policy could prove costly.
“Assuming you can find a DIC seismic insurance policy to cover a building located in an area prone to earth movement, the price would reflect the exposure,” Becerra said.
Underwriters rely on maps showing ground conditions, proximity to earthquake faults and other factors to determine rates, he said.
If the area is known to experience a lot of earth movement, he said, there may not be any companies willing to provide coverage.
“I wouldn’t guess the actual price, but I would expect it to be more than 1 percent of the coverage value and be subject to high deductibles,” Becerra said.