LANDSLIDES

Is attributed to its capacity to regulate rainwater infiltration, mitigate soil saturation, enhance soil strength increases slope stability.

For the second consecutive year, California has experienced abnormal amounts of rainfall due to “atmospheric river” storms that have pounded the state. The phenomenons have triggered hundreds of landslides in California's mountainous terrain, particularly in Northern and Southern California.

Vegetation:

Land formation

WATER AND FRICTION

GRAVITY

Southern California News Group

Top layer

Sublayer

The addition of water to material on a slope can make landslides more common. This is because water adds significant weight to the slope as it seeps into the ground, adding to the mass that is pulled by gravity. A buildup of groundwater lowers the strength of the material, which can make it less able to withstand the force of gravity. Water also reduces friction, making it easier to move material downhill. These processes help to explain why landslides are much more common during the rainy season, and especially common during or right after large storms.

Landslides nearly always move down a slope. This is because the force of gravity — which acts to move material downhill — is usually counteracted by two things: The internal strength of the material,.

The friction of the material on the slope. A landslide occurs when the driving forces (mass of earth and water pulled by gravity) in the slope exceed the resisting forces (friction, internal strength of rock or soil).

Landslides encompass five types of slope movement: falls, topples, slides, spreads and flows. These are further subdivided by the type of geologic material: bedrock, debris or earth.

Slope movement occurs when forces acting downslope — mainly due to gravity — exceed the strength of the earth materials that compose the slope. Landslides can be initiated by rainfall, snowmelt, changes in water level, stream erosion, changes in groundwater, earthquakes, volcanic activity, disturbance by human activities or any combination of these factors. Earthquake shaking and other factors can also induce landslides underwater.

Ground saturation

Landslides may not occur until weeks or months after a heavy rain. Heavy top layer can slip at the surface of sublayer

An average of 25 to 50 people are killed by landslides each year in the United States. The worldwide death toll per year due to landslides is in the thousands. Most landslide fatalities are from rock falls, debris flows, or volcanic debris flows (called lahars).