Why does water cause landslides

However, dry flows of granular material are also possible. Mudflow: A mudflow is an earthflow consisting of material that is wet enough to flow rapidly and that contains at least 50 percent sand-, silt-, and clay-sized particles. Creep: Creep is the imperceptibly slow, steady, downward movement of slope-forming soil or rock. Movement is caused by shear stress sufficient to produce permanent deformation, but too small to produce shear failure.

There are generally three types of creep: 1 seasonal, where movement is within the depth of soil affected by seasonal changes in soil moisture and soil temperature; 2 continuous, where shear stress continuously exceeds the strength of the material; and 3 progressive, where slopes are reaching the point of failure as other types of mass movements. Creep is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small soil ripples or ridges.

Lateral Spreads: Lateral spreads are distinctive because they usually occur on very gentle slopes or flat terrain. The dominant mode of movement is lateral extension accompanied by shear or tensile fractures. The failure is caused by liquefaction, the process whereby saturated, loose, cohesionless sediments usually sands and silts are transformed from a solid into a liquefied state.

Failure is usually triggered by rapid ground motion, such as that experienced during an earthquake, but can also be artificially induced. When coherent material, either bedrock or soil, rests on materials that liquefy, the upper units may undergo fracturing and extension and may then subside, translate, rotate, disintegrate, or liquefy and flow.

Lateral spreading in fine-grained materials on shallow slopes is usually progressive. The failure starts suddenly in a small area and spreads rapidly. Often the initial failure is a slump, but in some materials movement occurs for no apparent reason. Combination of two or more of the above types is known as a complex landslide. The two major types of slides are rotational slides and translational slides. Although there are multiple types of causes of landslides, the three that cause most of the damaging landslides around the world are these:.

Landslide Mitigation — How to Reduce the Effects of Landslides: Vulnerability to landslide hazards is a function of location, type of human activity, use, and frequency of landslide events. The effects of landslides on people and structures can be lessened by total avoidance of landslide hazard areas or by restricting, prohibiting, or imposing conditions on hazard-zone activity. Local governments can reduce landslide effects through land-use policies and regulations.

Individuals can reduce their exposure to hazards by educating themselves on the past hazard history of a site and by making inquiries to planning and engineering departments of local governments. They can also obtain the professional services of an engineering geologist, a geotechnical engineer, or a civil engineer, who can properly evaluate the hazard potential of a site, built or unbuilt. The hazard from landslides can be reduced by avoiding construction on steep slopes and existing landslides, or by stabilizing the slopes.

Stability increases when groundwater is prevented from rising in the landslide mass by 1 covering the landslide with an impermeable membrane, 2 directing surface water away from the landslide, 3 draining groundwater away from the landslide, and 4 minimizing surface irrigation. An advisory may include general statements about rainfall conditions that can lead to debris-flow activity, and list precautions to be taken in the event of heavy rainfall.

People in, or planning to travel through, a watch area should check preparedness and stay informed about developing weather patterns. Flash Flood Watches can be put into effect for as long as 12 hours, while heavy rains move into and across the area. A warning can also be issued as a result of torrential rains, a dam failure or snow thaw. GRAVITY — The natural force of attraction exerted by a celestial body, such as Earth, upon objects at or near its surface, tending to draw them toward the center of the body.

Click Here to see if there are any active warnings in your area. Get a ground assessment of your property. Landslides occur where they have before, and in identifiable hazard locations. Ask for information on landslides in your area, specific information on areas vulnerable to landslides, and request a professional referral for a very detailed site analysis of your property, and corrective measures you can take, if necessary. Watch the patterns of storm-water drainage near your home, and note the places where runoff water converges, increasing flow in channels.

These are areas to avoid during a storm. Make evacuation plans. Plan at least two evacuation routes since roads may become blocked or closed. Develop your own emergency plan for your family or business. Plant ground cover on slopes and build retaining walls. In mudflow areas, build channels or deflection walls to direct the flow around buildings. Design and construction of walls and channels strong enough to resist or divert landslides is highly specialized work, best done by qualified professionals.

Many debris-flow fatalities occur when people are sleeping. A landslide can involve rock, soil, vegetation, water, or some combination of all these. A landslide caused by a volcano can also contain hot volcanic ash and lava from the eruption. A landslide high in the mountains may have snow and snowmelt.

Volcanic landslides, also called lahar s, are among the most devastating type of landslides. The largest landslide in recorded history took place after the eruption of Mount St. Helens in the U. The resulting flow of ash, rock, soil, vegetation and water, with a volume of about 2. Another factor that might be important for describing landslides is the speed of the movement. Some landslides move at many meters per second, while others creep along at an centimeter or two a year.

The amount of water, ice, or air in the earth should also be considered. Some landslides include toxic gases from deep in the Earth expel led by volcanoes. Some landslides, called mudslide s, contain a high amount of water and move very quickly. Complex landslides consist of a combination of different material or movement types. A landslide can topple trees, rocks, even buildings. Photograph by Danielle Stevens, My Shot. Also called a mudflow. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.

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Interactives Any interactives on this page can only be played while you are visiting our website. Related Resources. The Rock Cycle. View Collection. Environmental Hazards. View Article. Pyroclastic Flow. But the fence posts continued to tip over, little by little, without anyone noticing the low part of the fence.

Until one day, about a month ago, a donkey got away by jumping over the low part of the fence. They helped their fathers fix the fence and straighten the fence posts so the donkey couldn't get away. Potential answers: There are many answers possible that don't relate to landslide hazards.

The fence could be old and the wood falling apart. The donkey could be pushing on the fence to eat some tasty grass that grows outside of that part of the fence. But the ground could also be moving very slowly beneath the farm, causing the fence posts to point uphill over the years. The fact that the spring stopped giving water may support this idea even further, especially if the path of the water to the surface was broken because the ground had shifted very slightly.

Gozen lives down in the city in a house. Sometimes all of the friends gather there to have dinner and listen to the radio or watch television. From where her family eats dinner, they can see the river. Her father helps to build and fix pipes that move water for farmers in the valley, and he also helps to build and fix houses. A wealthy man has just built a house above a very steep hill that has a beautiful view of the valley, and he even paid just to have electricity from the city strung on wires up the hill to the house.

But the rooms already have cracks in the walls on the side of the house near the steep hill. Some of the windows and doors have also become very difficult to open and close. Gozen's father has been working there the past few days and he jokes about how the wealthy man complains that his house was not built very well by workers from a nearby city. Potential answers: Again, the wealthy man may be right and the walls were indeed poorly built.

Oftentimes, houses also settle naturally as they age and cracks form as the house comes to rest on the ground. However, the cracks are forming on the walls on the sides nearest the steep hill, which may indicate that the part of the house that rests on ground above the steep hill may be on unstable ground that is slowly creeping down the hill.

Doors and windows can become difficult to open and close because the house is changing shape as the ground moves beneath it, causing the frames to become misshapen.

Also, if the ground was naturally unstable prior to building the house, the added load of the new house may be speeding the rate of movement of the creeping slope.

Unstable ground or ground that is creeping is much more likely to release during a triggering event such as an earthquake or heavy rainfall. There are many ways to tell what the real cause of the cracks may be.

Other indications, such as the bending of pipes, fences, footpaths, or roads, can be found to see if the ground is moving. If the ground is shifting, then electrical wires attached to polls in the ground near the edge of the hill will become very tight as the polls move with the ground.

One day, the three friends decide to go play in the forest together. They travel farther up the hill than they had ever gone before. They find a very interesting bunch of very tall trees whose trunks grow out of the ground at an angle before the trees turn straight and point up into the air like a normal tree figure 2. Some of the trees have such a sharp angle that the girls can sit in the angle of the trees like a comfortable chair with their feet dangling down the slope of the hill!

Most of the trees are curved in the same direction in the middle. The three friends name it the Sideways Forest. Figure 2: A common tree shape formed due to ground creep Potential answers: Trees always grow up toward sunlight, so presumably the trees initially grew at a different angle when they were young.

The fact that the trees were all curved in the same direction, and that they were all located next to each other, might indicate that the ground beneath the Sideways Forest is all shifting in one direction. The trees are all much older than the girls, implying that the ground has been moving for a very long time. This might mean that the ground above the farm is unstable and could be dislodged in the event of heavy rain, an earthquake, or human activities like road construction.

Figure 2 shows the shape of a tree that may indicate a history of ground creep, when exhibited by groups of trees located together. One day, while the friends are walking back home from school, there is an earthquake. It is strong enough to shake many of the buildings around them, and the earthquake is over after about a minute.

They are just as far away from Gozen's home as from Sara's and Amira's farms. Potential answers: There are many reasons to go to Gozen's house first. Gozen has a radio and television, so they can hear about the damage caused by the earthquake and whether emergency services are being delivered. The radio or television, if they are functioning immediately after the earthquake, may also have information on any developing weather system that may be coming in that could make the situation created by the earthquake even worse, such as heavy rain or snowfall.

In addition, the combination of observations the girls have noticed around Amira's and Sara's farms indicate that the ground might be unstable and prone to landslide if another earthquake occurs. Knowing that the farmland is unstable, it is natural for the girls to want to make sure that their families and homes are safe.

At that moment it is very dangerous to go there because the possibility for aftershocks is high. Since the girls are safe, they should first make contact with a parent or family friend to let their parents know they are safe and find out what has happened in order that they can make an informed decision about what to do next, while conserving water, food, and medical supplies.

The families are all fine, and they meet at Gozen's house to talk about what happened. Through the radio they find out that there has been an earthquake that has caused numerous landslides throughout the region.

The neighbor whose land was becoming soaked with water reported that, in some places on his land, the surface had broken into cracks and the smooth slope had become shaped like stairs. The road has been blocked by some falling rocks, but the families have some food stored away for when the road is closed. Gozen's dad says that many pipes have been broken in several places, so there is no water to be gathered through the city's water system. They send the friends down to the river to gather some water to support the families.

While the three friends are at the river, they notice that the water level is much lower than it had been the day before. Potential answers: In river valleys that are likely to experience landslides after earthquakes, a sudden decrease in river water levels may indicate a landslide dam has formed upstream of the city. A landslide dam occurs when a landslide has blocked a river or stream, causing water to build up behind it. This causes flooding upstream and a drought or decreased water flow downstream.

Landslide dams can be extremely dangerous because they are usually highly unstable. As the water builds up behind the dam, the landslide becomes saturated with water and can break catastrophically, flooding all areas downstream with little or no warning. Recall the instability of water-saturated unconsolidated materials observed during the liquefaction exercise in Lesson 7. The three friends should notify their parents or other city officials immediately of this possibility so that they can determine whether a landslide dam has formed.

Landslides cause fatalities and property damage throughout the Nation. To reduce the impact from hazardous landslides, the U. Geological Survey develops and uses real-time and near-real-time landslide monitoring systems. Monitoring can detect when hillslopes are primed for sliding and can provide early indications of rapid, catastrophic movement This handbook is intended to be a resource for people affected by landslides to acquire further knowledge, especially about the conditions that are unique to their neighborhoods and communities.

Considerable literature and research are available concerning landslides, but unfortunately little of it is synthesized and integrated to address the This set of videos presents about 18 hours of footage documenting the experiments conducted at the USGS debris-flow flume from to Owing to improvements in video technology over the years, the quality of footage from recent experiments generally exceeds that from earlier experiments.

Use the list below to access the individual videos Landslides occur and can cause damage in all 50 States. Severe storms, earthquakes, volcanic activity, coastal wave attack, and wildfires can cause widespread slope instability. Landslide danger may be high even as emergency personnel are providing rescue and recovery services. To address landslide hazards, several questions must be considered Southern California lies astride a major tectonic plate boundary defined by the San Andreas Fault and numerous related faults that are spread across a broad region.

This dataset consists of polygons enclosing areas of landslide incidence and susceptibility for the conterminous United States. The accompanying landslide overview map of the conterminous United States is one of a series of National Environmental Overview Maps that summarize geologic, hydrogeologic, and topographic data essential to the assessment of national environmental problems. The map delineates areas where large numbers of landslides exist and areas which are A new landslide guidebook released February 5 is now available for Puerto Rico residents to learn more about the landslide hazards that can impact the island.

Geological Survey today unveiled a new web-based interactive map that marks an important step toward mapping areas that could be at higher risk for future landslides. In collaboration with state geological surveys and other federal agencies, USGS has compiled much of the existing landslide data into a searchable, web-based interactive map called the U. Landslide Inventory Map. A new "Science for Everyone" article summarizes a recent publication about the potential of landslide-triggered tsunamis in Glacier Bay National Park and Preserve.

The following is an updated version of a story first published in March of The USGS uses cutting edge technologies to investigate and forecast landslides and other natural hazards. Landslides and debris flows could happen in areas where intense rainfall occurs. Big Sur Landslide fly around from May 27, , a preliminary computer animation.

The slide created roughly 13 acres of new California land. Photograph from aerial survey showing the upper parts of the landslide in northwest Washington. Photograph showing landslides covering State Route 1 near Ohau Point. The route was impacted my several landslides and is the main north-south highway on the eastern part of the South Island of New Zealand.

As many as 80, landslides occurred as the result of a magnitude 7. The earthquake and landslides caused. Debris flows are hazardous flows of rock, sediment and water that surge down mountain slopes and into adjacent valleys. Spectacular debris flow footage, recorded by Franck Lavigne of the.

Laser scanning the entire Cleveland Corral landslide from across the valley during an active spring Repeat scans are used to detect movement throughout the slide. Skip to main content. Search Search. Natural Hazards.