landslides California bay area coast

1/11/17

The rain may have slowed, but now that the soil is drenched, the threat of landslide remains high. Please be safe out there, folks!


Landslides are a yearly threat to residents of the Bay Area. The region's sudden, strong autumnal rainstorms and steep slopes can combine to make the perfect landslide conditions. Learn what you can do to prepare for them and how to reduce your risk. 

On this page:
The Causes of Landslides
How to Protect Your Property from a Landslide
How to Ensure the Integrity of Your Home’s Foundation
Understanding Bay Area Landslide Risk
Safety Infographic
Further Reading on Landslides

            

Photo: Engineered Soil Repairs, Inc., 2016 

CAUSES
The Causes of Landslides

By Christopher Wilhite, chief engineer and co-owner of Engineered Soil Repairs, Inc.

landslide engineering walls
Engineered Soil Repairs works to repair the damage caused by a landslide in Lafayette. Photo: Engineered Soil Repairs, Inc., 2016

What causes landslides?
Ninety-nine percent of the time, landslides are caused by water affecting the stability of a slope. There are two basic forces that determine slope stability:
1. Driving Force. This force wants to push the soil mass downhill. It’s a function of the weight of the soil and the steepness of the slope.
2. Resisting Force. This force tries to keep the soil from moving downhill. It’s the internal friction between the soil mass that wants to slide and the mass of soil below, which is stable. When the driving force is greater than the resisting force, you have a landslide.

Why does water cause landslides?
When water is introduced to the soil (i.e. from rain or a water pipe break), it fills the tiny void spaces between soil particles and adds weight to the soil. This weight increases the driving force. At the same time, water reduces the resisting force by reducing friction. Essentially, the soil gets slick at the point of contact between the soil mass that wants to slide and the soil mass that’s stable. When certain types of soil become saturated, they lose all strength and behave like a liquid, flowing down the slope. This is what’s known as a mudslide... Read more 

PROPERTY
How to Protect Your Property from a Landslide

car drives in landslide area
Hire a professional to evaluate the drainage on your property. Photo: Doug Morton, U.S. Geological Survey.

If you think your property is at risk:

 1. Learn about the history of your property. Areas that have experienced landslides in the past are likely to experience them again. Your city may keep records of past landslides, and you can also try this landslide inventory-mapping tool (in beta) from the California Department of Conservation...
Read More

FOUNDATIONS
How to Ensure the Integrity of Your Home’s Foundation

landslide foundation home drainage
Adequate drainage is essential for maintaining a strong and stable home foundation. Photo: Dimension Construction Inc, 2016

While a concrete foundation may be the proverbial rock upon which a house is built, even this seemingly indestructible component can be vulnerable to damage and failure. When it comes to upgrading your home’s foundation, there are two main factors to consider: retrofitting and drainage... Read more

 

Find a Diamond Certified Company to Help You Prepare for Landslides
UNDERSTANDING RISK
Understanding Bay Area Landslide Risk

landslide Bay Bridge retaining wall
The same geophysical forces that created the Bay Area’s dramatic scenery are also responsible for its landslide risk. Photo: Engineered Soil Repairs, Inc., 2016

Dr. Ross Stein is scientist emeritus at the United States Geological Survey, an adjunct professor of geophysics at Stanford University and the cofounder of Temblor.net, a startup that enables users to freely access data about their natural catastrophe risk.

With the rainy season fast approaching, we sat down with geophysicist Dr. Ross Stein to discuss how Bay Area homeowners can better understand and mediate their risk for landslides. Of course, the Bay Area is known for its beautiful scenery and temperate weather, but it’s also known for frequent seismic activity and landslides. Dr. Stein has been studying the Bay Area for more than four decades, and he says both the region’s beauty and susceptibility to disasters come courtesy of the same force: the San Andreas Fault. Just as the San Andreas Fault is to blame for the Bay Area’s notorious earthquakes, it has also created conditions that make the Bay Area especially vulnerable to landslides.

Dr. Stein says two central factors precipitate landslides: steep slopes and loosely packed soil, both of which typify the Bay Area’s geology. He also points to a third factor that increases landslide risk: rain. As we move into the cooler, wetter months, the region becomes more vulnerable. Dr. Stein identifies the Santa Cruz Mountains region—with its steep terrain, loosely packed soil, and greater exposure to rain and fog—as an area that’s especially at risk for landslides. “But even areas that are relatively flat are susceptible,” he adds. “Measurements in downtown Berkeley have identified shifting soil, which indicates the area is at risk.” 
Read more 

STAY SAFE
How to Stay Safe During a Landslide

LANDSLIDE SAFETY INFOGRAPHIC 

 

LEARN MORE
Further Reading on Landslides