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1 Protect Your Home and Property Washington Geological Survey and Oregon Department of Geology and Mineral Industries for Washington and Oregon A Homeowner’s Guide to Landslides LANDSLIDES ARE ONE OF THE MOST COMMON AND DEVASTATING NATURAL HAZARDS IN THE PACIFIC NORTHWEST. THE DAMAGE THEY CAUSE IS ALMOST NEVER COVERED BY INSURANCE. ---PAGE BREAK--- 2 www.dnr.wa.gov/geology sewer line water line Quick Facts About Landslides WHAT IS A LANDSLIDE? A landslide is the downward slope movement of rock, soil, or debris. Debris flow, earth flow, rock fall, mudflow, mudslide, slide, and slump are also terms for landslide. READ ON TO LEARN SEVERAL THINGS YOU CAN DO TO REDUCE YOUR RISK LANDSLIDES CAN TAKE HUMAN LIFE. HOWEVER, EVEN A FEW INCHES OF SLOPE MOVEMENT CAN DISRUPT SEPTIC, SEWER, AND WATER LINES AND CRACK FOUNDATIONS, SEVERELY DAMAGING OR DESTROYING YOUR HOME WHY SHOULD I CARE? ---PAGE BREAK--- 3 www.oregongeology.org COMMON TYPES OF LANDSLIDES Rotational slides occur when rock or earth is transported downslope along a curved surface. This type of landslide can be large and damaging. and debris flows are usually rapid, downward movements of mixtures of water, soil, rock and (or) debris. Flows often occur in either water-saturated slopes or where vegetation has been removed by fire or humans. Common Landslide Types ---PAGE BREAK--- 4 www.dnr.wa.gov/geology Triggers LANDSLIDES HAPPEN IN AREAS WITH STEEP SLOPES, AND ARE TYPICALLY TRIGGERED BY EVENTS LIKE THESE WAV E OR STREAM E ROSI ON BEL OW BLUFFS EA RT H QU AKE S ---PAGE BREAK--- 5 www.oregongeology.org excavating the base of slopes overwatering runoff Triggers saturated soil INTENSE OR PROLONGED RAINFALL AND (OR) RAPID SNOWMELT HUMAN ACTIVITIES ---PAGE BREAK--- 6 www.dnr.wa.gov/geology Landslides in the Landscape hummocky topography SLID E PL AN E tilted and pistol-butted trees new spring or seep sunken or broken road SIGNS OF LANDSLIDE ACTIVITY: ● ●Cracks in soil ● ●Tilted or bent trees ● ●Increased spring activity or newly wet ground ● ●Hummocky or uneven terrain ● ●Sagging or taut utility lines ● ●Sunken or broken road beds ● ●Movement of soil away from foundations ● ●Leaking or broken water pipes IF YOU SUSPECT ACTIVE LANDSLIDE MOVEMENT: EVACUATE AND CONTACT YOUR LOCAL FIRE, POLICE, EMERGENCY MANAGER, OR PUBLIC WORKS DEPARTMENT ---PAGE BREAK--- 7 www.oregongeology.org Landslides in the Landscape ‘sag’ pond newly forming headscarp sagging or taut utility lines mid-slope benches leaking or broken water pipes cracks in soil wet slopes or springs gaps in soil at foundation GROUND CRACKING THE PRESENCE OF A PREVIOUS LANDSLIDE IS ONE OF THE BIGGEST AND MOST OBVIOUS RISK FACTORS ---PAGE BREAK--- 8 www.dnr.wa.gov/geology WHY IS WATER IMPORTANT? One cubic foot (7.5 gallons) of water weighs 62.3 lbs! When water is added to a slope the weight increases the downward force, putting surrounding homes at risk 62.3 lbs The Role of Water n a ti v e Dry soil grains touch, increasing soil strength Wet soil grains pushed apart reducing soil strength REDUCE WATER ON SLOPES: ● ●Maintain healthy vegetation ● ●Use drought-resistant plantings ● ●Fix leaking plumbing immediately ● ●Direct downspout runoff well away from slopes ● ●Plant trees and shrubs, which uptake water more efficiently than lawns ---PAGE BREAK--- 9 www.oregongeology.org buffer zone DEEP ROOT SYSTEMS GIVE STRENGTH TO SLOPES e t re e s a nd pl an ts Trees and Plants MAINTAIN A BUFFER OF NATIVE PLANTS BETWEEN YOUR HOUSE AND THE EDGES OF STEEP SLOPES Live tree roots strengthen slopes. After a tree is cut down, it takes between 5 and 8 years for the roots below to lose their strength. PLANT ROOTS ARE VITAL ---PAGE BREAK--- 10 www.dnr.wa.gov/geology Reduce Your Risk THERE ARE ACTIONS YOU CAN TAKE AS A HOMEOWNER TO REDUCE THE CHANCES OF A LANDSLIDE AFFECTING YOUR PROPERTY: DO DO NOT ● ●Drain water from surface runoff, downspouts, and driveways well away from slopes ● ●Plant native ground cover on slopes ● ●Consult with a professional before significantly altering existing slopes uphill or downslope of your home ● ●If you suspect you are on a landslide, contact a licensed engineering geologist or a geotechnical engineer for an evaluation ● ●Check online maps, such as SLIDO (Oregon) or the Washington Geologic Information Portal to see if you might live in a landslide area ● ●Do not add water to steep slopes ● ●Avoid placing fill soil on or near steep slopes ● ●Avoid placing yard waste or debris on steep slopes ● ●Avoid excavating on or at the base of steep slopes YOU AND YOUR NEIGHBORS SHARE MORE THAN FENCES. YOU ALL SHARE THE RESPONSIBILITY OF KEEPING YOUR SLOPES SAFE. ---PAGE BREAK--- 11 www.oregongeology.org Property Checklist If you live on or near a steep slope, evaluate your property for signs of landslide movement. Many (but not all) signs of landslide activity are listed below. A high score may indicate the presence of a landslide. INSIDE YOUR HOME: ͌ ͌ Cracks in walls ͌ ͌ Nails popping out of walls ͌ ͌ Bulging walls ͌ ͌ Separation of chimney from walls ͌ ͌ Creaking/popping noises ͌ ͌ Light switches coming out of walls ͌ ͌ Doors/windows hard to shut ͌ ͌ Twisted beams ͌ ͌ Cracks in floors ͌ ͌ Water seeping into basement OUTSIDE YOUR HOME: ͌ ͌ Changes in surface drainage ͌ ͌ Bulges in retaining walls or tilting of walls ͌ ͌ Cracks developing in the soil ͌ ͌ Pistol-butted or bent trees ͌ ͌ Broken water, utility, or sewer lines ͌ ͌ Cracks in sidewalks or foundation ͌ ͌ Stretched or leaning utility lines CONSULT A PROFESSIONAL BEFORE PURCHASING PROPERTY IN SLOPING AREAS pistol - b u t t e v e r gree n tr e e s LOOK FOR WARNING SIGNS ON YOUR PROPERTY ---PAGE BREAK--- For More Information IF YOU ARE IMPACTED BY OR SUSPECT AN ACTIVE LANDSLIDE: ● ●Evacuate ● ●Contact your local fire, police, emergency manager, or public works department ● ●Contact a licensed professional U.S. GEOLOGICAL SURVEY Landslide Hazards Program landslides.usgs.gov WASHINGTON STATE DEPARTMENT OF ECOLOGY Slope Stabilization and Erosion Control Using Vegetation www.ecy.wa.gov/programs/sea/ pubs/93-30 http://www.dnr.wa.gov/ programs-and-services/ geology/geologic-hazards/ landslides Oregon Department of Geology and Mineral Industries THIS PAMPHLET WAS MADE IN COOPERATION WITH WASHINGTON GEOLOGICAL SURVEY Washington Geologic Information Portal www.dnr.wa.gov/geologyportal OREGON DEPARTMENT OF GEOLOGY AND MINERAL INDUSTRIES SLIDO Landslide Information Database www.oregongeology.org/sub/slido LANDSLIDE RESOURCES This pamphlet offers some general guidance a homeower should consider regarding their home and property. Landslide conditions vary from site to site—if you are concerned about your property, it is always best to consult a professional.