WHAT IS A LANDSLIDE?

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2 WHAT IS A LANDSLIDE?

3 WHAT IS A LANDSLIDE?

4 WHAT IS A LANDSLIDE?

5 WHAT IS A LANDSLIDE? Landslides occur when masses of rock, earth, or debris move down a slope. Landslides may be very small or very large, and can move at slow to very high speeds. Many landslides have been occurring over the same terrain since prehistoric times. They are activated by storms and fires and by human modification of the land. New landslides occur as a result of rainstorms. earthquakes, volcanic eruptions, and various human activities.

6 What do we mean by the word "landslide"? Landslide is a general term used to describe the down-slope movement of soil, rock and organic materials under the influence of gravity. It also describes the landform that results. As our cities, towns, roads and highways steadily encroach onto steeper slopes and mountainsides, landslide hazards become an increasingly serious threat to life and property. However, by understanding the answers to the following questions, we may be able to lessen the effects of landslides.

7 WHAT IS A LANDSLIDE? Landslides are a serious geologic hazard common to almost every state in the United States. It is estimated that nationally they cause up to $2 billion in damages and from 25 to 50 deaths annually. Globally, landslides cause billions of dollars in damage and thousands of deaths and injuries each year. Individuals can take steps to reduce their personal risk. Know about the hazard potential where you live, take steps to reduce your risk, and practice preparedness plans. Some landslides move slowly and cause damage gradually, whereas others move so rapidly that they can destroy property and take lives suddenly and unexpectedly. Gravity is the force driving landslide movement. Factors that allow the force of gravity to overcome the resistance of earth material to landslide movement include: saturation by water, steepening of slopes by erosion or construction, alternate freezing or thawing, earthquake shaking, and volcanic eruptions. Landslides are typically associated with periods of heavy rainfall or rapid snow melt and tend to worsen the effects of flooding that often accompanies these events. In areas burned by forest and brush fires, a lower threshold of precipitation may initiate landslides..

8 WHAT IS A LANDSLIDE? Debris flows, sometimes referred to as mudslides, mudflows, lahars, or debris avalanches, are common types of fast-moving landslides. These flows generally occur during periods of intense rainfall or rapid snow melt. They usually start on steep hillsides as shallow landslides that liquefy and accelerate to speeds that are typically about 10 miles per hour, but can exceed 35 miles per hour. The consistency of debris flows ranges from watery mud to thick, rocky mud that can carry large items such as boulders, trees, and cars. Debris flows from many different sources can combine in channels, and their destructive power may be greatly increased. They continue flowing down hills and through channels, growing in volume with the addition of water, sand, mud, boulders, trees, and other materials. When the flows reach flatter ground, the debris spreads over a broad area, sometimes accumulating in thick deposits that can wreak havoc in developed areas.

9 WHAT IS A MUDFLOW? Mudflows (or debris flows) are rivers of rock, earth, and other debris saturated with water. They develop when water rapidly accumulates in the ground, such as during heavy rainfall or rapid snowmelt, changing the earth into a flowing river of mud or "slurry." A slurry can flow rapidly down slopes or through channels, and can strike with little or no warning at avalanche speeds. A slurry can travel several miles from its source, growing in size as it picks up trees, cars, and other materials along the way.

10 Landslide and mudflows Landslide and mudflows usually strike without warning. The force of rocks, soil, or other debris moving down a slope can devastate anything in its path. Take the following steps to be ready.

11 What causes landslides?

12 Landslide Types Landslides or slope movements can be classified in many ways. There are many attributes used as criteria for identification and classification including: Rate of movement: This ranges from very slow creep (millimetres/year) to extremely rapid (metres/second). Type of material: Landslides are composed of bedrock, unconsolidated sediment and/or organic debris. Nature of movement: The moving debris can slide, slump, flow or fall.

13 Landslide Types Common landslide types are: Slide: movement parallel to planes of weakness and occasionally parallel to slope. Creep: gradual movement of slope materials

14 Common landslide types are: Slump: complex movement of materials on a slope; includes rotational slump. Topple: the end-over-end motion of rock down a slope

15 Common landslide types are: Fall: material free falls. Flow: viscous to fluid-like motion of debris Flow: viscous to fluidlike motion of debris

16 Common landslide types are: Torrent::a sporadic and sudden channelized discharge of water and debris.

17 The Vaiont Landslide in the Dolomites (The Dolomites are a mountain range in Northern Italy)

18 The Vaiont Landslide in the Dolomites (The Dolomites are a mountain range in Northern Italy) This map shows the scale of the landslide, which slopped the contents of the reservoir over the dam and killed more than 2000 people in Longarone and the adjoining communities

19 What should you do before the landslide? How to Protect Your Property? Get a ground assessment of your property. Your county geologist or county planning department may have specific information on areas vulnerable to landsliding. Consult a professional geotechnical expert for opinions and advice on landslide problems and on corrective measures you can take. Minimize home hazards. Plant ground cover on slopes and build retaining walls. In mudflow areas, build channels or deflection walls to direct the flow around buildings. Remember: If you build walls to divert debris flow and the flow lands on a neighbor's property, you may be liable for damages.

20 What should you do before the landslide? Learn to recognize the landslide warning signs. Doors or windows stick or jam for the first time. New cracks appear in 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. Bulging ground appears at the base of a slope. Water breaks through the ground surface in new locations. Fences, retaining walls, utility poles, or trees tilt or move. You hear a faint rumbling sound that increases in volume as the landslide nears.the ground slopes downward in one specific direction and may begin shifting in that direction under your feet.

21 What should you do before the landslide? Make evacuation plans. Plan at least two evacuation routes since roads may become blocked or closed. Develop an emergency communication plan. In case family members are separated from one another during a landslide or mudflow this is (a real possibility during the day when adults are at work and children are at school), have a plan for getting back together. Ask an out-of-state relative or friend to serve as the "family contact". After a disaster, it's often easier to call long distance. Make sure everyone knows the name, address, and phone number of the contact person. Insurance Mudflow is covered by flood insurance policies from the National Flood Insurance Program. Flood insurance can be purchased through a local insurance agency.

22 What should you do during the landslide? If inside a building: Stay inside. Take cover under a desk, table, or other piece of sturdy furniture. If outdoors: Try and get out of the path of the landslide or mudflow. Run to the nearest high ground in a direction away from the path. If rocks and other debris are approaching, run for the nearest shelter such as a group of trees or a building. If escape is not possible, curl into a tight ball and protect your head. Sinkholes A sinkhole occurs when groundwater dissolves a vulnerable land surface such as limestone, causing the land surface to collapse from a lack of support. In June 1993, a 100-foot wide, 25-foot deep sinkhole formed under a hotel parking lot in Atlanta, killing two people and engulfing numerous cars.

23 What should you do during the landslide? Stay alert and awake. Many debris-flow fatalities occur when people are sleeping. Listen to a NOAA Weather Radio or portable, battery-powered radio or television for warnings of intense rainfall. Be aware that intense, short bursts of rain may be particularly dangerous, especially after longer periods of heavy rainfall and damp weather. If you are in areas susceptible to landslides and debris flows, consider leaving if it is safe to do so. Remember that driving during an intense storm can be hazardous. If you remain at home, move to a second story if possible. Staying out of the path of a landslide or debris flow saves lives. Listen for any unusual sounds that might indicate moving debris, such as trees cracking or boulders knocking together. A trickle of flowing or falling mud or debris may precede larger landslides. Moving debris can flow quickly and sometimes without warning. If you are near a stream or channel, be alert for any sudden increase or decrease in water flow and for a change from clear to muddy water. Such changes may indicate landslide activity upstream, so be prepared to move quickly. Don't delay! Save yourself, not your belongings. Be especially alert when driving. Embankments along roadsides are particularly susceptible to landslides. Watch the road for collapsed pavement, mud, fallen rocks, and other indications of possible debris flows.

24 What should you do after the landslide? Stay away from the slide area. There may be danger of additional slides. Check for injured and trapped persons near the slide, without entering the direct slide area. Direct rescuers to their locations. Help a neighbor who may require special assistance - infants, elderly people, and people with disabilities. Elderly people and people with disabilities may require additional assistance. People who care for them or who have large families may need additional assistance in emergency situations. Listen to local radio or television stations for the latest emergency information. Watch for flooding, which may occur after a landslide or debris flow. Floods sometimes follow landslides and debris flows because they may both be started by the same event.

25 What should you do after the landslide? Look for and report broken utility lines to appropriate authorities. Reporting potential hazards will get the utilities turned off as quickly as possible, preventing further hazard and injury. Check the building foundation, chimney, and surrounding land for damage. Damage to foundations, chimneys, or surrounding land may help you assess the safety of the area. Replant damaged ground as soon as possible since erosion caused by loss of ground cover can lead to flash flooding. Seek the advice of a geotechnical expert for evaluating landslide hazards or designing corrective techniques to reduce landslide risk. A professional will be able to advise you of the best ways to prevent or reduce landslide risk, without creating further hazard.

26 What should you do after the landslide?

27 Landslide and mudflows Mitigation Mitigation includes any activities that prevent an emergency, reduce the chance of an emergency happening, or lessen the damaging effects of unavoidable emergencies. Investing in preventive mitigation steps now such as planting ground cover (low growing plants) on slopes, or installing flexible pipe fitting to avoid gas or water leaks, will help reduce the impact of landslides and mudflows in the future. For more information on mitigation, contact your local emergency management office.

28 How can we minimize the effects of landslides? The Role of the Geoscientist and Engineer: Landslide risk can be reduced with engineering and geoscience investigations that lead to improved community bylaws and zoning. The British Columbia Municipal Act contains legal requirements that deal with landslides and other hazards. By geological mapping, detecting slope hazards and determining the likelihood of landslide occurrence, geoscientists can assist engineers, developers, planners and building inspectors in avoiding high-risk areas. Through this process, structures such as homes, schools, hospitals, power-lines, fire stations and roads can be safely located away from potential landslide risk areas.

29 How can we minimize the effects of landslides? Your Role: Learn more about your local geology and the potential geologic hazards in your area. Consult an engineer or geoscientist with relevant experience in landslide work for advice or information on specific hazards and potentially hazardous locations. Avoid activities that result in the undercutting of steep banks, and avoid the construction of buildings near the top or base of steep slopes. Do not place fill on steep slopes. Request information and assistance from your municipal or district planner or building inspector prior to land purchase, prior to subdividing, and prior to construction applications.

30 How can we minimize the effects of landslides? Property damage in the Qualicum Beach area after a landslide (photo courtesy of the Ministry of Environment, Lands and Parks).

31 How do landslides affect us? Landslides cause property damage, injury and death and adversely affect a variety of resources. For example, water supplies, fisheries, sewage disposal systems, forests, dams and roadways can be affected for years after a slide event. The negative economic effects of landslides include the cost to repair structures, loss of property value, disruption of transportation routes, medical costs in the event of injury, and indirect costs such as lost timber and lost fish stocks. Water availability, quantity and quality can be affected by landslides. Geotechnical studies and engineering projects to assess and stabilize potentially dangerous sites can be costly.

32 How do landslides affect us? In 1991, a rock slide near Loggers Creek closed the Sea-to-Sky Highway for 12 days and cost $7 million for repairs and preventative structures (photo courtesy of the Ministry of Transportation and Highways). A debris torrent at Britannia Creek in August of 1991 caused extensive damage to property (photo courtesy of K. Fletcher).

33 Landslide losses The Vancouver to Squamish highway has been affected by 14 major debris torrents since Twelve lives have been lost and 11 bridges, 4 homes and numerous structures have been damaged or destroyed. Not one of these 14 slide events was larger than cubic metres (photo courtesy of the Ministry of Transportation and Highways).

34 HELP YOUR COMMUNITY GET READY The media can raise awareness about landslide and mudflows by providing important information to the community. Here are some suggestions: In an area prone to landslides, publish a special section with emergency information on landslides and mudflows. Localize the information by including the phone numbers of local emergency services offices, the American Red Cross, and hospitals. Report on what city and county governments are doing to reduce the possibility of landslides. Interview local officials about local land-use zoning regulations. Interview local officials and major insurers regarding the National Flood Insurance Program. Remind your community that mudflow is covered by flood insurance policies from the National Flood Insurance Program. Work with local emergency services and American Red Cross officials to prepare special reports for people with mobility impairments on what to do if an evacuation is ordered.

35 DID YOU KNOW... The most expensive landslide in U.S. history occurred in Thistle, Utah, in spring, It reached 1/2 miles from top to bottom and ranged in width from 1,000 feet to about 1 mile. Total costs attributable to the landslide exceeded $500 million. Landsliding in the United States is estimated to cause an annual loss of about $1.5 billion and at least 25 fatalities. The Loma Prieta earthquake in October 1989 triggered thousands of landslides throughout an area of 5,400 square miles. In addition to causing at least tens of millions of dollars of damage to houses, other structures, and utilities, landslides blocked many transportation routes, greatly hampering rescue and relief efforts. Mudflows tend to flow in channels, but will often spread out over a floodplain. They generally occur in places where they have occurred before.

36 EMERGENCY INFORMATION Acres of property may be damaged and buildings and homes destroyed by landslides. Landslides can provoke associated dangers such as broken electrical, water, gas, and sewage lines, and disrupt roadways and railways. Landslide warning signs include cracks opening on hillslopes, evidence of slow, downhill movement of rock and soil; tilting of trees, poles, or walls; or visible changes such as the formation of sags and bumps in the slope. Landslide, mudflow, and debris-flow problems are often caused by land mismanagement. Improper land-use practices on ground of questionable stability, particularly in mountain, canyon, and coastal regions, can create and accelerate serious landslide problems. Land-use zoning in partnership with professional inspections and proper design can alleviate many problems associated with landslides, mudflows, and debris flows.

37 FEATURES THAT MAY INDICATE CATASTROPHIC LANDSLIDE MOVEMENT What to do and look for during and immediately after heavy rains? What to Do Before Intense Storms

38 What to Do Before Intense Storms? Become familiar with the land around you. Learn whether landslides and debris flows have occurred in your area by contacting local officials, state geological surveys or departments of natural resources, and university departments of geology. Knowing the land can help you assess your risk for danger. Watch the patterns of storm-water drainage on slopes near your home, and especially the places where runoff water converges, increasing flow over soil-covered slopes. Watch the hillsides around your home for any signs of land movement, such as small landslides or debris flows, or progressively tilting trees. Watching small changes could alert you to the potential of a greater landslide threat.

39 Areas that are generally prone to landslide hazards On existing old landslides. On or at the base of slopes. In or at the base of minor drainage hollows. At the base or top of an old fill slope. At the base or top of a steep cut slope. Developed hillsides where leach field septic systems are used

40 Areas that are typically considered safe from landslides On hard, non-jointed bedrock that has not moved in the past. On relatively flat-lying areas away from sudden changes in slope angle. At the top or along the nose of ridges, set back from the tops of slopes.

41 Features that might be noticed prior to major landsliding Springs, seeps, or saturated ground in areas that have not typically been wet before. New cracks or unusual bulges in the ground, street pavements or sidewalks. Soil moving away from foundations. Ancillary structures such as decks and patios tilting and/or moving relative to the main house. Tilting or cracking of concrete floors and foundations. Broken water lines and other underground utilities. Leaning telephone poles, trees, retaining walls or fences Offset fence lines. Sunken or down-dropped road beds. Rapid increase in creek water levels, possibly accompanied by increased turbidity (soil content). Sudden decrease in creek water levels though rain is still falling or just recently stopped. Sticking doors and windows, and visible open spaces indicating jambs and frames out of plumb.

42 What to do if you suspect imminent landslide danger? Contact your local fire, police, or public works department. Local officials are the best persons able to assess potential danger. Inform affected neighbors. Your neighbors may not be aware of potential hazards. Advising them of a potential threat may help save lives. Help neighbors who may need assistance to evacuate. Evacuate. Getting out of the path of a landslide or debris flow is your best protection.

43 For further information on landslides in your area Contact your County Geologist--Some cities also staff geologists. Contact your State Geologist or Engineer If a very detailed site analysis is desired, contract with a private consulting company specializing in earth movement Such companies would likely be those specializing in geotechnical engineering, structural engineering, or civil engineering. Your, Local, state, or county geologist could possibly advise you as to the best kind of professional to contact.

44 How The Public Can Help After A Disaster? When disaster strikes, people everywhere want to help those in need. To ensure that this compassion and generosity are put to good use, the media can highlight these facts: Financial aid is an immediate need of disaster victims. Financial contributions should be made through a recognized voluntary organization to help ensure that contributions are put to their intended use. Before donating food or clothing, wait for instructions from local officials. Immediately after a disaster, relief workers usually don't have time or facilities to setup distribution channels, and too often these items go to waste. Volunteers should go through a recognized voluntary agency such as the American Red Cross or Salvation Army. They know what is needed and are prepared to deal with the need. Local emergency services officials also coordinate volunteer efforts for helping in disasters. Organizations and community groups wishing to donate items should first contact local officials, the American Red Cross, or Salvation Army to find out what is needed and where to send it. Be prepared to deliver the items to one place, tell officials when you'll be there, and provide for transportation, driver, and unloading.

45 LANDSLIDE AVOIDANCE

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47 Landslide Deflection Rockfalls (above) and rockslides (below - this is a slide of rock debris) are an ever present danger in areas of high relief. It such terrain, it is impossible to regrade slopes to stable angles. The scale of landsliding may be too great to do anything about its causes - we can only try to reduce its effects. In the diagram above we have the major elements of a rockfall. There is a source area, in this case a layer of jointed rock. The joints open - why? Several mechanisms suggest themselves. Firstly, water - or ice - in the joints can cause pressures. Secondly, if the rock warms in the sun, the mass expands and joints open. Any dirt or gravel which falls into the joints stops them closing when the rock next cools. Thirdly, the stratum could be undermined. This could be because of erosion. It could be that the underlying rock softens or weathers. The mass then collapses. We call the accumulation of rockfall debris a scree or talus. Screes form at F=1, and are thus incredibly easy to destabilise - but that is a different problem.

48 Landslide Deflection One approach to the problem from rockfalls or debris slides is to construct a concrete structure to deflect rockslide or rockfall debris. They are widely employed in mountainous areas to protect both roads and railways. I would like to see an example protecting a canal! The debris is deflected over the route to be protected. The roof is thick reinforced concrete, and it is made with a slope to throw off the debris. Sometimes a layer of crushed rock or gravel is left on the roof. This protects it against impact from large blocks. An alternative, where impact on the roof is a problem, is to use old tyres to absorb the impact... NB. The photos are higher resolution image than I have displayed them. If you right-click on them, you get the chance to view (or save) at higher resolution. The examples are all from Taiwan

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51 In the town of Lamosano, threatened by the Tessina landslide, a concrete flume has been built to carry the landslide through the village! Water can be injected into the base of the landslide to keep it moving. This is the flume.