Upper Park Road
Santa Cruz, CA 95065
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
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
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.
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
Remove rocks from slopes, if they might roll downhill during a heavy rainfall
Check adjacent slopes during heavy or prolonged rains for early signs of
slippage or formation of mud flows
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
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
If there is time before evacuation, turn off all utilities at the main
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.
Danger has Passed
Thoroughly check the foundation, chimney and surrounding land to be sure
no damage has occurred.
Check for damaged gas, electrical or water lines.
Report damage to the appropriate utility companies.
Replanting damaged land will help tremendously in both
short and long term
Check buildings for cracks and damage, including roof, chimney and
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
701 Ocean Street
Santa Cruz, CA 95060
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
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
will the County of Santa Cruz be liable for any damages whatsoever,
direct, consequential, incidental, special or on claim for attorney fees
arising out of the use of or inability to use the information provided
You can email us at Office
of Emergency Services