495 Upper Park Road
Santa Cruz, CA 95065
Phone: (831) 458-7150
Fax: (831) 458-7139

Office Hours:
M-F 8:00 a.m to 12:00 Noon
1:00 p.m. to 5:00 p.m.

Landslide and Mudflow Dangers

A landslide or slope failure is defined as a downward and outward movement of soil and rock. Such a movement occurs when steep slopes are destabilized by excess water accumulation in the soil, the addition of excess weight to the top of a slope, the removal of support from the bottom of a slope, or a combination of the above. 
Landslides area a common occurrence in the Santa Cruz Mountains. Our intense winter storms, high rainfall amounts, and steep terrain area all conductive to land sliding. Earthquake activity adds to the problem.  The big earthquake of 1906 set off dozens of large landslides in the Santa Cruz Mountains, some of which claimed human lives. The potential for loss of life and property is much greater today. 

Although nature caused landslides are beyond control, most recent landslides in the Santa Cruz Mountains have been caused by a combination of human activity and natural factors. Human activities which act to further destabilizing slopes are logging, woodland conversion, road building, housing construction, and any activity which alters normal drainage patterns. Whether or not any of these activities will trigger land sliding depends on the existing natural conditions. Some soil and rock types are more prone to land sliding than others, and landowners should determine the inherent geologic stability of their property before beginning construction activities. 

Landslides, mud flows and debris avalanches frequently accompany other natural disasters such as floods and earthquakes. It is important to learn to recognize the warnings signs of possible landslides in your immediate area.

Signs and Warnings

Recognition and avoidance of existing landslide deposits and potential slide areas is the best means of prevention. Unstable areas may sometimes be identified by trees or telephone poles tilted at odd angles, or by curved tree trunks. Other signs to look for are unnatural benches or bowl shaped depressions on otherwise uniformly sloping hillsides, indicators of surface water accumulation such as springs or water loving plants, and cracks in the ground.

Homeowners with hillside homes can recognize the beginnings of slope failure through the following indicators:
 

• doors or windows that start to stick or jam 

• new cracks in walls, foundations, driveways, etc.

• outside walls, walks, or stairs that have pulled away from the building

• widening of previously patched cracks in driveways or yards

• creaking and groaning sounds

• breakage of underground utility lines

• leakage from swimming pools

Potential slide areas are usually on steep slopes or improperly prepared fill slopes, although some soil types such as Bay wood loamy sand (the Aromas Red Sands) are so unstable that even relatively gentle slopes may fail.

Several tools have been developed to help land users identify unstable slopes. Slope maps, geology maps, and landslide deposit maps are available for public inspection at the Santa Cruz County Planning Department. Although these maps are valuable for the general location of unstable areas, they can not be substituted for a careful on site investigation.  Such an investigation can be performed by a registered Geologist. A list of consulting geologist who have done similar work for the County is available from the County Geologist in the Planning Department.

Preparedness

• Avoid building on a steep slope, close to its edge, or immediately in front of it, unless geological conditions are determined by experts to be safe.

• Do not build in or near the course of swales or drainage ways on slopes that could carry mud flows in heavy storms

• Avoid unnecessary watering of slopes, especially those with a thick soil cover

• Remove rocks from slopes, if they might roll downhill during a heavy rainfall or earthquake

• Check adjacent slopes during heavy or prolonged rains for early signs of slippage or formation of mud flows

In addition, 

• Prepare to evacuate if you are instructed to do so.

• Stock your car with nonperishable foods, a plastic container of water, blankets, first aid kit, warm clothing, flashlight, portable radio, copies of important papers and any special medication needed by members of your family.

• keep the gas tank at least half full at all times

• Do not return until you have been notified by proper authorities that is safe to do so.

• Make family evacuation plans. Have several alternate routes to ensure rapid evacuation.


If there is time before evacuation, turn off all utilities at the main switch.

Mud flows

Mud flows which are often referred to as "debris  flows" or "mudslides" are caused by sustained and intense rain fall that is accompanied by rocks, vegetation and other debris. These are fast moving down slope flows and can cause severe damage.   The rapid movement and sudden arrival of debris flows pose a hazard to life and property during and immediately following the triggering rain fall. 
In order to trigger "debris flows" a storm must have a critical combination of rainfall intensity and duration leading to saturation of the hill slope soils, generation of positive pore fluid pressures within the soil and ultimately, slope failure.

After the Danger has Passed

La Officia de Servicios de Emergencia del condado de Santa Cruz tiene personal que habla Español.

This information has been prepared by the Santa Cruz County Resource Conservation District in cooperation with the United States Department of Agriculture Soil Conservation Service and the Santa Cruz County Planning Department. For further local assistance in landslide and erosion prevention, please call :

      Santa Cruz County Planning Department
      att: County Geologist
      701 Ocean Street 4th Floor
      Santa Cruz, CA 95060
      (831) 454-2580

For more information contact the National Landslide Information Center (NLIC) at 1-800-654-4966, the United States Geological Survey Office in your area  USGS Information , California Floods 98 .

The County of Santa Cruz makes no representations or warrants as to the suitability of this information for your particular purpose, and that to the extent you use or implement this information in your own setting you do so at your own risk.  The information provided herewith is solely for your own use and cannot be sold.  In no event will the County of Santa Cruz be liable for any damages whatsoever,  whether direct,  consequential,  incidental,  special or on claim for attorney fees arising out of the use of or inability to use the information provided herewith.

You can email us at Office of Emergency Services