Landslide and Mudflow Dangers
Landslides, mudflows and debris avalanches frequently accompany other natural hazards
such as floods and earthquakes. The October 17, 1989 earthquake resulted in many areas
of unstable land throughout the County which will be further impacted by winter storm
Signs and Warnings
Major landslides are usually accompanied by a faint rumbling sound that increases in
volume as the landslide approaches. Also, the ground will pitch in one direction only
and may begin shifting in that direction under your feet.
Mudflows and/or debris avalanches may follow rain.
If your home is on a hill, you can detect possible slop failure if you watch for these
Doors or windows stick or jam for the first time.
New Cracks appear on plaster, tile, brick or foundations.
Outside walls, walks or stairs begin pulling away from the building.
Slowly developing, widening cracks appear on the ground or on paved areas such
as streets or driveways.
Underground utility lines break.
Fences, retaining walls, utility poles or trees tilt or move.
Water or bulging ground appears at the base of a slope.
Reinforce the foundation and walls of your home. Identify vulnerable areas of your
home and add temporary shoring, bracing or shear wall supports where necessary.
Install flexible rather than stiff pipe fitting to avoid gas or water leaks in the event of a
landslide or mudflow.
Mudflow is covered by flood insurance policies from the National Flood Insurance
Program (NFIP). You can buy flood insurance even if you do not live in the flood
plain. Keep your insurance coverage up to date.
Stockpile emergency building supplies such as ropes, buckets, large plastic bags,
plywood, sandbags, plastic sheeting and lumber.
Maintain emergency supplies such as water, foods that require little cooking, a first
aid kit, portable radio and flashlights.
In high risk areas, construct channels to direct the mudflows around your home or
If you are inside during a landslide and the building is not in peril of sliding down a
hill, stay inside and get under a desk, table or other sturdy furniture.
If you are outside and cannot get into a sturdy building while rocks and debris
tumble toward you, curl into a tight ball and protect your head.
Usually, you can survive a mudflow or debris avalanche only by avoiding it. If
you are in a valley, get out as soon as possible once you hear rumbling from
upstream or feel the ground tremble. These are signs that a mudflow may be
coming your way.
If caught in a mudflow, try grabbing onto a large rock, tree or anything being
Prepare to Evacuate
If you are warned of an impending landslide or mudflow, evacuate at once.
Stock your car with nonperishable foods (like canned goods), a plastic container of
water, blankets, first aid kit, warm clothing, a 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 the proper authorities that it is
safe to do so.
Make family evacuation plans. Have several alternate routes to insure rapid evacuation.
If there is time before evacuation, turn off all utilities at the main switch.
After the Danger is Past
If a landslide or mudflow has occurred near your home, 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
Stabilization of new land should take place as quickly as possible to reinforce against
Replanting damaged land will help tremendously in both short- and long-term