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A landslide is a large amount of earth, rock, and other material that moves down a steep slope. Landslides happen when a layer of earth or rocks separates from the layer below it. The force of gravity pulls the loose layer downward.

Landslides can be highly destructive. They can bury or sweep away everything in their path. They can block rivers or cover entire towns.

A landslide needs a steep slope to get its start. Rain, wind, waves, and other natural processes can wear away the surface of a slope. This wearing away, or erosion, can make a slope too steep to support the rocks and earth on top. Erosion can also loosen or weaken the material on a slope. This makes it easier for gravity to pull the material down the slope.

Besides erosion, other forces can lead to landslides. Rainstorms, melting snow, and earthquakes can weaken the material on a slope. Earthquakes, volcanoes, and the use of construction equipment or explosives can force material down a slope.

Rockfalls, mudflows, and avalanches are similar to landslides. A rockfall involves large rocks falling from the top of a slope or a cliff. A mudflow is a thick stream of mud and other material that moves quickly downward. An avalanche is the sudden downward movement of snow or other material.

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A landslide is a large amount of earth, rock, and other material that moves down a steep slope. Landslides happen when a layer of earth or rocks separates from the layer...

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What is a wildfire?
A wildfire also known as a wildland fire, forest fire, vegetation fire, grass fire, peat fire, bushfire (in Australia), or hill fire is an uncontrolled fire often occurring in wildland areas, but which can also consume houses or agricultural resources. Wildfires often begin unnoticed, but they spread quickly igniting brush, trees and homes.

What causes a wildfire?
Common causes of wildfires include lightning, human carelessness, arson, volcano eruption, and pyroclastic cloud from active volcano. Heat waves, droughts, and cyclical climate changes such as El Niño can also have a dramatic effect on the risk of wildfires. Although, more than four out of every five wildfires are caused by people.

Where can wildfires occur?
Wildfires can occur anywhere, but are common in the forested areas of the United States and Canada. They are also susceptible in many places around the world, including much of the vegetated areas of Australia as well as in the Western Cape of South Africa. The climates are sufficiently moist to allow the growth of trees, but feature extended dry, hot periods. Fires are particularly prevalent in the summer and fall, and during droughts when fallen branches, leaves, and other material can dry out and become highly flammable. Wildfires are also common in grasslands and scrublands.

What are the Santa Ana winds?
The Santa Ana winds are hot, dry winds that aggravate the fire danger in forests and bush lands. These winds characteristically appear in Southern California and Northern Baja California weather during autumn and early winter. In southern California, under the influence of Santa Ana winds, wildfires can move at tremendous speeds, up to 40 miles in a single day, consuming up to 1,000 acres per hour. Dense clouds of burning embers push ahead of the flames crossing firebreaks without a problem.

What is a fire tornado?
A fire tornado or fire whirl is just a tornado made of fire. It happens when certain conditions (depending on air temperature and currents), acquires a vertical vorticity and forms a whirl, or a tornado-like effect. Fire tornadoes may be whirlwinds separated from the flames, either within the burn area or outside it. A fire tornado can make fires more dangerous.

How do firefighters put out the wildfires?
Firefighters use a tool known as a pulaski. Its a combination of an ax and hoe used to dig a fireline. A fireline is a strip of land from which all brush and debris have been cleared to rob a wildfire of its fuel. Firefighters also use hotshots and smoke jumpers to clear a large path in a big circle around the fire so the blaze is contained in a ring of dirt. When the fire reaches this area, it runs out of fuel and starves to death. If the fire is too large, however, planes and helicopters fly overhead, dropping water and special chemicals that smother the flames. This pink, fire-retardant chemical is called sky jell-o.

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SURFACE FIRES - The most common type of wildfires, surface fires move slowly and burn along the forest floor, killing and damaging vegetation.

GROUND FIRES - These are usually started by lightning, ground fires burn on or below the forest floor through the root system.

CROWN FIRES - These fires spread by wind moving quickly along the tops of trees.

SANTA ANA WINDS - "Santa Ana" is the name given to the gusty northeast or east wind that occurs in Southern California during the fall and winter months. Santa Ana winds are often hot and very dry, greatly aggravating the fire danger in forests and bush lands.

CONFLAGRATION - A large and destructive fire, typically aggravated by strong winds that carry firebrands over natural or artificial barriers.

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BEFORE A WILDFIRE: Have a disaster plan. Know whether you're in a wildfire prone area. Plant fire resistant shrubs and trees around your home. Have a garden hose that is long enough to reach around your home. Prepare a disaster supplies kit for your home and car. Include a first aid kit, canned food and a can opener, bottled water, battery-operated radio, flashlight, protective clothing and written instructions on how to turn off electricity, gas, and water. Always listen to the radio and television for the latest information and instructions for your area.

DURING A WILDFIRE: If you're advised to evacuate then do so immediately. Wear protective clothing and lock your home. Tell someone you left and where you are going. Choose a safe route away from fire hazards. Watch for changes in the speed and direction of fire and smoke.

AFTER A WILDFIRE: Stay away from wildfire areas until it is safe.

Lesson Plan: Here is a great lesson plan on teaching students to have an escape plan if a fire threatens their home.

Science Fair Project Ideas: Here is a complete list of science fair project ideas. Discover the science behind the weather that impacts us every day.

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What is a wildfire? A wildfire also known as a wildland fire, forest fire, vegetation fire, grass fire, peat fire, bushfire (in Australia), or hill fire is an uncontrolled fire often occurring in wildland areas, but which can also consume houses or agricultural resources.

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Did you know fires move faster when traveling uphill? Explore these interesting wildfire facts for kids from the experts at the Western Fire Chiefs Association (WFCA).

A wildfire is an uncontrolled fire that starts burning in wildland, such as a forest, grassland, or the edge of an urban area. Firefighters focus on protecting human lives, structures, and resources when they battle wildfires. ¹ Learn some wild facts about wildfires and remember: always be careful with fire.

Fact #1

Humans cause 89% of annual wildfires.²

Most wildfires are caused by humans and can result from many kinds of activities. For example, a stray ember from a campfire can spark a blaze, or a spark from a car engine can ignite dry grass. Not all human-caused fires are accidental. Starting a fire on purpose, to hurt the environment, buildings, or people, is called arson. Arson is against the law and can have terrible consequences.

Sometimes, firefighters will very carefully light fires on purpose in order to clear overgrown plants and help nature thrive. ³ However, these burns are handled by professionals in controlled conditions. A wildfire, on the other hand, is unplanned and extremely dangerous. Even if fires start small, it is difficult to predict if they will become large, destructive wildfires that threaten human lives and communities.

Fact #2

You need three things for a fire to start: heat, oxygen, and a fuel source.

Firefighters call heat, air, and fuel the fire triangle. These three things combined can create ignition and start a fire. ⁴ Sources of heat can be cigarettes, a spark from a campfire or a gas-powered tool like a chainsaw, or even the sun. Fuel can be the dry wood you use to make a campfire, or it can be plants and grasses. Dry weather, especially droughts, and windy days make wildfires more likely and more dangerous.

Fact #3

Wildfires move at an average of 14 miles per hour.

The speed of a wildfire varies depending on the terrain, the type of fuel available, and weather conditions. ⁵ Rising smoke and heat can dry out fuel further up the slope of a hill, so fire burns more quickly uphill. Wildfires can also quickly get out of control when flames move from the ground to the tops of trees.

Fact #4

Wildfires can happen anywhere in the United States.

Wildfires happen more frequently in the central U.S. and on the East Coast, but wildfires that happen in the Western states (Alaska, Arizona, California, Colorado, Idaho, Montana, New Mexico, Nevada, Oregon, Utah, Washington, and Wyoming) are larger. Many Western state fires happen in undeveloped areas and tend to burn more acres than wildfires in other parts of the U.S. ²

Fact #5

Wildfires burn 5-10 million acres in the United States every year.

In the U.S., there has been a 223% increase in the amount of land burned by wildfires annually since 1983, when official wildfire record-keeping began. Wildfires in 1983 burned 1.3 million acres of land; in 2021, there were 7.1 million acres burned by wildfires. ⁶

Fact #6

Lightning is the biggest natural cause of wildfires.

There are two types of lightning: cold and hot. Cold lightning has an intense electrical current but does not last very long and rarely starts fires. Hot lighting has a weaker electrical current, but the bolt of lightning stays for a longer period of time. These longer-lasting bolts can cause wildfires. 7 Even though humans cause most wildfires, fires started by lightning are usually larger and burn more land. ²

Fact #7

Wildfires can take many shapes-even tornados!

Wildfires move, spread, and grow in several different ways.

Ground fires burn dead plant debris from the forest floor. These fires can burn for a long time without being detected because they burn so slowly and produce very little smoke. They can even burn through tree roots.

Surface fires happen when a fire burns slowly across a forest floor. This type of fire kills living vegetation and tree saplings.

Crown fires happen when winds, or fuel sources like vines, bring fire to the tops of trees. This type of fire spreads fast as the wind blows flames from treetop to treetop.⁸

Tornado fires are an extreme fire behavior. They are created by air temperature shifts and wind current changes. Flames can burn inside or outside of the tornado. These types of fires can grow very quickly.⁹

Fact #8

Fire is part of the ecosystem and helps maintain forests.

Fire is essential for the health of wildlands, just like rain and snow have their place in the natural cycle. It can even help certain trees spread their seeds. Giant sequoias are the largest trees on Earth, but they need fire in order to spread. Fire makes space in the forest for more light and water to reach sequoia seedlings. The mature trees are sturdy enough to withstand smaller, more frequent wildfires, and the heat from fires opens the cones to release sequoia seeds. ¹⁰ Firefighting in wild areas now includes regular, controlled burns that clear debris and potential fuel from the landscape. This work ensures that fire can benefit the environment while being safely managed. ¹

Fact #9

Extreme wind patterns cause wildfires to spread and grow rapidly.

The Rocky Mountains run from New Mexico to Canada. This huge mountain range creates strong wind currents. These winds are called Santa Ana winds when they move west towards Southern California ¹¹ and Chinook winds when they move east towards Colorado and Montana. 12 These winds can blow at 60-100 miles per hour and have fanned wildfires to dangerous heights in nearby states in just minutes.

Fact #10

The annual number of wildfires in the United States is decreasing, but the amount of acres burned by wildfires is going up.

Since 2000, wildfires have burned an average of 7 million acres every year-more than double the average amount of acres burned in the 1990s. However, the average number of annual wildfires in the 1990s was 78,600, while the current average number of annual wildfires is 70,000. ²

Sources

1. National Park Service, "Wildland Firefighting Tactics." Accessed December 14, 2022.

2. Congressional Research Service, "Wildfire Statistics." Accessed January 10, 2023.

3. National Park Service, "Types of Wildland Fire." Accessed December 14, 2022.

4. Firetrace, "What are the Different Stages of a Fire?" Accessed December 12, 2022.

5. Mercury Insurance, "How Wildfires Start and Spread." Accesses October 25, 2022.

6. Bankrate, "U.S. Wildfire Statistics 2022." Accessed January 10, 2023.

7. National Park Service, "Wildfire Causes and Evaluations." Accessed January 9, 2023.

8. Northwest Fire Science Consortium, "What are Types of Fire?" Accessed January 11, 2023.

9. Library of Congress, "Can a tornado be made out of fire?" Accessed January 11, 2023.

10. PBS, "Why the Giant Sequoia Needs Fire to Grow." Accessed January 10, 2023.

11. Science, "California's fire-fanning Santa Ana winds may not get any better with climate change." Accessed January 11, 2023.

12. Live Science, "What Are Chinook Winds?" Accessed January 11, 2023.

Related Article

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Did you know fires move faster when traveling uphill? Explore these interesting wildfire facts for kids from the experts at the Western Fire Chiefs Association (WFCA).

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A wildfire, or wildland fire, is an uncontrolled fire in a forest, grassland, brushland, or other sparsely populated area. Terms such as forest fire and brush fire may be used to describe specific types of wildfires. In Australia they are called bushfires.

Wildfires can be catastrophic, and they are often considered to be natural disasters. About 90 percent of them, however, are ignited by people, either by accident or on purpose. Accidental wildfires are started by unattended campfires, discarded cigarettes, or other careless behavior. Intentionally set wildfires are the result of arson. Only 10 percent of wildfires are started by natural causes, such as lightning or lava.

Fire danger in a wildland setting varies with weather conditions. Drought, heat, and wind dry out grass, leaves, and light branches, making them easier to ignite. Fire spreads quickly in these materials, which are known as flash fuels. The burning of flash fuels can create enough heat to ignite heavier fuels such as tree stumps and heavy branches. Once these heavy fuels are burning, it is hard to put the fire out. Green fuels-growing trees and plants-are not considered flammable, but an intense fire can dry out leaves and needles quickly enough to allow them to catch fire. Drought, heat, and wind all increase the intensity of a wildfire. The landscape also affects wildfire, which spreads quickly uphill and slowly downhill.

U.S. Air Force photo by Staff Sgt. Stephany D. Richards/U.S. Department of Agriculture

© University of Melbourne, Victoria, Australia

Tools for fighting wildfires include portable pumps, tank trucks, and earth-moving equipment. Airplanes and helicopters are also very important in fighting wildfires. They are used for dumping water or other chemicals that can slow down or contain wildfires. Aircraft are also used for gathering information and for moving people, supplies, and equipment. Technology has come to play an increasingly important role in combating wildfires. Forest managers and firefighters use satellites to detect fires in their early stages and to track fires in progress. They also use computer models to predict a fire's path.

U.S. Air Force photo by Master Sgt. Jeremy Lock/U.S. Department of Agriculture

Firefighting forces specially trained to deal with wildfires are maintained by public and private owners of forestlands. Such a force may attack a fire directly by spraying water and beating out flames. They may also try to stop the fire from spreading by removing vegetation at the edge of the fire. The cleared strip of land is called a fire line or firebreak. When the edge of the fire is too hot to approach, firefighters create a fire line at a safe distance. Sometimes they use a technique called backfiring, which involves setting controlled fires to eliminate fuel in the path of the wildfire. Backfiring is used only as a last resort.

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A wildfire, or wildland fire, is an uncontrolled fire in a forest, grassland, brushland, or other sparsely populated area. Terms such as forest fire and brush fire may be used to describe specific types of wildfires. In Australia they are called bushfires. Wildfires can be catastrophic, and they are often considered to be natural disasters.

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What is a landslide?
A landslide is defined as the movement of a mass of rock, debris, or earth down a slope due to gravity. The materials may move by falling, toppling, sliding, spreading, or flowing.

What causes a landslide?
Almost every landslide has multiple causes. Slope movement occurs when forces acting down-slope (mainly due to gravity) exceed the strength of the earth materials that compose the slope. Landslides can be triggered by rainfall, snowmelt, changes in water level, stream erosion, changes in ground water, earthquakes, volcanic activity, disturbance by human activities, or any combination of these factors.

What are submarine landslides?
Earthquake shaking and other factors can also induce landslides underwater. These landslides are called submarine landslides. Submarine landslides sometimes cause tsunamis that damage coastal areas.

Where do landslides occur?
Landslides in the United States occur in all 50 States. The primary regions of landslide occurrence and potential are the coastal and mountainous areas of California, Oregon, and Washington, the States comprising the intermountain west, and the mountainous and hilly regions of the Eastern United States. Alaska and Hawaii also experience all types of landslides.

How fast do landslide travel?
Landslides can move slowly, (millimeters per year) or can move quickly and disastrously, as is the case with debris flows. Debris flows can travel down a hillside at speeds up to 200 miles per hour (more commonly, 30 - 50 miles per hour), depending on the slope angle, water content, volume of debris, and type of earth and debris in the flow. These flows are initiated by heavy periods of rainfall, but sometimes can happen as a result of short bursts of concentrated rainfall or other factors in susceptible areas. Burned areas charred by wildfires are particularly susceptible to debris flows, given certain soil characteristics and slope conditions.

Why study landslides?
Landslides are a serious geologic hazard. It is estimated that in the United States they cause in excess of $1 billion in damages and from about 25 to 50 deaths each year. Globally, landslides cause billions of dollars in damages and thousands of deaths and injuries each year.

Who is most at risk for landslides?
As people move into new areas of hilly or mountainous terrain, it is important to understand the nature of their potential exposure to landslide hazards, and how cities, towns, and counties can plan for land-use, engineering of new construction and infrastructure, and other measures which will reduce the costs of living with landslides. Although the physical causes of many landslides cannot be removed, geologic investigations, good engineering practices, and effective enforcement of land-use management regulations can reduce landslide hazards.

Do human activities cause landslides?
Yes, in some cases human activities can be a contributing factor in causing landslides. Many human-caused landslides can be avoided or mitigated. They are commonly a result of building roads and structures without adequate grading of slopes, of poorly planned alteration of drainage patterns, and of disturbing old landslides.

Where can I find landslide information for my area?
The USGS National Landslide Information Center (NLIC) is a part of the U.S. Geological Survey Landslide Hazards Program that collects and distributes all forms of information related to landslides. The NLIC is designed to serve landslide researchers, geotechnical practitioners engaged in landslide stabilization, and anyone else concerned in any way with landslide education, hazard, safety, and mitigation. Every state in the US has a geoscience agency and most have some landslide information. The Association of American State Geologists provides links to the State Geologist for every state.

What was the most expensive landslide to fix in the United States?
The Thistle, Utah, landslide cost in excess of $200 million dollars to fix. The landslide occurred during the spring of 1983, when unseasonably warm weather caused rapid snowmelt to saturate the slope. The landslide destroyed the railroad tracks of the Denver and Rio Grande Western Railway Company, and the adjacent Highway 89. It also flowed across the Spanish Fork River, forming a dam. The impounded river water inundated the small town of Thistle. The inhabitants of the town of Thistle, directly upstream from the landslide, were evacuated as the lake began to flood the town, and within a day the town was completely covered with water. Populations downstream from the dam were at risk because of the possible overtopping of the landslide by the lake. This could cause a catastrophic outburst of the dam with a massive flood downstream. Eventually, a drain system was engineered to drain the lake and avert the potential disaster.

How many deaths result from landslides?
An average of between 25 and 50 people are killed by landslides each year in the United States. The worldwide death toll per year due to landslides is in the thousands. Most landslide fatalities are from rock fall, debris-flows, or volcanic debris flows.

What should I know about wildfires and debris flows?
Wild land fires are inevitable in the western United States. Expansion of human development into forested areas has created a situation where wildfires can adversely affect lives and property, as can the flooding and landslides that occur in the aftermath of the fires. There is a need to develop tools and methods to identify and quantify the potential hazards posed by landslides produced from burned watersheds. Post-fire landslide hazards include fast-moving, highly destructive debris flows that can occur in the years immediately after wildfires in response to high intensity rainfall events, and those flows that are generated over longer time periods accompanied by root decay and loss of soil strength. Post-fire debris flows are particularly hazardous because they can occur with little warning, can exert great impulsive loads on objects in their paths, and can strip vegetation, block drainage ways, damage structures, and endanger human life. Wildfires could potentially result in the destabilization of pre-existing deep-seated landslides over long time periods.

How do landslides cause tsunamis?
Tsunamis are large, potentially deadly and destructive sea waves, most of which are formed as a result of submarine earthquakes. They may also result from the eruption or collapse of island or coastal volcanoes and the formation of giant landslides on marine margins. These landslides, in turn, are often triggered by earthquakes. Tsunamis can be generated on impact as a rapidly moving landslide mass enters the water or as water displaces behind and ahead of a rapidly moving underwater landslide.

What are some examples of landslides that have caused tsunamis?
The 1964 Alaska earthquake caused 115 deaths in Alaska alone, with 106 of those due to tsunamis generated by tectonic uplift of the sea floor, and by localized subareal and submarine landslides. The earthquake shaking caused at least 5 local slide-generated tsunamis within minutes after the shaking began. An eyewitness account of the tsunami caused by the movement and landslides of the 1964 Alaska earthquake.

Research in the Canary Islands concludes that there have been at least five massive volcano landslides that occurred in the past, and that similar large events may occur in the future. Giant landslides have the potential of generating large tsunami waves at close and also very great distances and would have the potential to devastate large areas of coastal land as far away as the eastern seaboard of North America.

Rock falls and rock avalanches in coastal inlets, such as those that have occurred in the past at Tidal Inlet, Glacier Bay National Park, Alaska, have the potential to cause regional tsunamis that pose a hazard to coastal ecosystems and human settlements. On July 9, 1958, a magnitude M 7.9 earthquake on the Fairweather Fault triggered a rock avalanche at the head of Lituya Bay, Alaska. The landslide generated a wave that ran up 524 m on the opposite shore and sent a 30-m high wave through Lituya Bay, sinking two of three fishing boats and killing two persons.

How soon does the danger of landslides end after the rain stops?
It's not possible to exactly predict the number of days or weeks that landslides remain a danger after heavy rain. Residents near mountain slopes, canyons, and landslide prone areas should stay alert even after heavy rain subsides.

Why is southern California vulnerable to landslides?
Areas that have been burned by recent wildfires are highly susceptible to debris-flow activity that can be triggered by significantly less rainfall than that which triggers debris flows from unburned hill slopes.

What was the biggest landslide in the world?
The world's biggest historic landslide occurred during the 1980 eruption of Mount St. Helens, a volcano in the Cascade Mountain Range in the State of Washington, USA. The volume of material was 2.8 cubic kilometers (km).

What was the biggest prehistoric landslide?
The world's biggest prehistoric landslide, discovered so far on land, is in southwestern Iran, and is named the Saidmarreh landslide. The landslide is located on the Kabir Kuh anticline in Southwest Iran at 33 degrees north latitude, 47.65 degrees east longitude. The landslide has a volume of about 20 cubic kilometers, a depth of 300 m, a travel distance of 14 km and a width of 5 km. This means that about 50 billion tons of rock moved in this single event!

Rotational slide: This is a slide in which the surface of rupture is curved concavely upward and the slide movement is roughly rotational about an axis that is parallel to the ground surface and transverse across the slide.

Translational slide: In this type of slide, the landslide mass moves along a roughly planar surface with little rotation or backward tilting.

Block slide: is a translational slide in which the moving mass consists of a single unit or a few closely related units that move downslope as a relatively coherent mass.

Fall: Falls are abrupt movements of masses of geologic materials, such as rocks and boulders, that become detached from steep slopes or cliffs. Separation occurs along discontinuities such as fractures, joints, and bedding planes, and movement occurs by free-fall, bouncing, and rolling. Falls are strongly influenced by gravity, mechanical weathering, and the presence of interstitial water.

Topple: Toppling failures are distinguished by the forward rotation of a unit or units about some pivotal point, below or low in the unit, under the actions of gravity and forces exerted by adjacent units or by fluids in cracks.

Debris flow: A debris flow is a form of rapid mass movement in which a combination of loose soil, rock, organic matter, air, and water mobilize as a slurry that flows downslope. Debris flows include less than 50% fines. Debris flows are commonly caused by intense surface-water flow, due to heavy precipitation or rapid snowmelt, that erodes and mobilizes loose soil or rock on steep slopes. Debris flows also commonly mobilize from other types of landslides that occur on steep slopes, are nearly saturated, and consist of a large proportion of silt- and sand-sized material. Debris-flow source areas are often associated with steep gullies, and debris-flow deposits are usually indicated by the presence of debris fans at the mouths of gullies. Fires that denude slopes of vegetation intensify the susceptibility of slopes to debris flows.

Debris avalanche: This is a variety of very rapid to extremely rapid debris flow.

Earthflow: Earthflows have a characteristic "hourglass" shape. The slope material liquefies and runs out, forming a bowl or depression at the head. The flow itself is elongate and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and under saturated conditions. 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. In some instances, for example in many newspaper reports, mudflows and debris flows are commonly referred to as "mudslides."

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.

SLIDES: Although many types of mass movements are included in the general term "landslide," the more restrictive use of the term refers only to mass movements, where there is a distinct zone of weakness that separates the slide material from more stable underlying material. The two major types of slides are rotational slides and translational slides.

FLOWS: There are five basic categories of flows that differ from one another in fundamental ways. Although there are multiple types of causes of landslides, the three that cause most of the damaging landslides around the world are these:

Landslides and Water: Slope saturation by water is a primary cause of landslides. This effect can occur in the form of intense rainfall, snowmelt, changes in ground-water levels, and waterlevel changes along coastlines, earth dams, and the banks of lakes, reservoirs, canals, and rivers. Landsliding and flooding are closely allied because both are related to precipitation, runoff, and the saturation of ground by water. In addition, debris flows and mudflows usually occur in small, steep stream channels and often are mistaken for floods; in fact, these two events often occur simultaneously in the same area. Landslides can cause flooding by forming landslide dams that block valleys and stream channels, allowing large amounts of water to back up. This causes backwater flooding and, if the dam fails, subsequent downstream flooding. Also, solid landslide debris can "bulk" or add volume and density to otherwise normal streamflow or cause channel blockages and diversions creating flood conditions or localized erosion. Landslides can also cause overtopping of reservoirs and/or reduced capacity of reservoirs to store water.

Landslides and Seismic Activity: Many mountainous areas that are vulnerable to landslides have also experienced at least moderate rates of earthquake occurrence in recorded times. The occurrence of earthquakes in steep landslide-prone areas greatly increases the likelihood that landslides will occur, due to ground shaking alone or shaking- caused dilation of soil materials, which allows rapid infiltration of water. The 1964 Great Alaska Earthquake caused widespread landsliding and other ground failure, which caused most of the monetary loss due to the earthquake. Other areas of the United States, such as California and the Puget Sound region in Washington, have experienced slides, lateral spreading, and other types of ground failure due to moderate to large earthquakes. Widespread rockfalls also are caused by loosening of rocks as a result of ground shaking. Worldwide, landslides caused by earthquakes kill people and damage structures at higher rates than in the United States.

Landslides and Volcanic Activity: Landslides due to volcanic activity are some of the most devastating types. Volcanic lava may melt snow at a rapid rate, causing a deluge of rock, soil, ash, and water that accelerates rapidly on the steep slopes of volcanoes, devastating anything in its path. These volcanic debris flows (also known as lahars) reach great distances, once they leave the flanks of the volcano, and can damage structures in flat areas surrounding the volcanoes. The 1980 eruption of Mount St. Helens, in Washington triggered a massive landslide on the north flank of the volcano, the largest landslide in recorded times.

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. Slope stability is also increased when a retaining structure and/ or the weight of a soil/rock berm are placed at the toe of the landslide or when mass is removed from the top of the slope.

LANDSLIDE ADVISORY - a general statement about the potential of landslide activity in a given region relative to developing rainfall predictions. 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.

LANDSLIDE WATCH - means that landslide-activity will be possible, but is not imminent. People in, or planning to travel through, a watch area should check preparedness and stay informed about developing weather patterns.

LANDSLIDE WARNING - indicates that landslide activity is presently occurring and extreme caution should be taken.

FLOOD WATCH - means that an overflow of water from a river is possible for your area.

FLASH FLOOD WATCH - means that flash flooding is possible in or close to the watch area. Flash Flood Watches can be put into effect for as long as 12 hours, while heavy rains move into and across the area.

FLOOD WARNING - means flooding conditions are actually occurring in the warning area.

FLASH FLOOD WARNING - means that flash flooding is actually occurring in the warning area. A warning can also be issued as a result of torrential rains, a dam failure or snow thaw.

URBAN and SMALL STREAM ADVISORY - means flooding of small streams, streets and low-lying areas, such as railroad underpasses and urban storm drains is occurring.

DEBRIS - The scattered remains of something broken or destroyed; rubble or wreckage.

DEBRIS FLOW - A churning, water-saturated mass of rock, soil and organic matter that rushes down mountain slopes, typically originating as a landslide.

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.

FRICTION - Force that resists the relative motion or tendency to such motion of two bodies in contact.

TRIGGER - An event that initiates a landslide.

Click Here to see if there are any active warnings in your area.

BEFORE A LANDSLIDE: Avoid building near steep slopes, close to mountain edges, near drainage ways, or natural erosion valleys. 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.

MINIMIZE HOME HAZARDS: Have flexible pipe fittings installed to avoid gas or water leaks, as flexible fittings are more resistant to breakage. 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. Design and construction of walls and channels strong enough to resist or divert landslides is highly specialized work, best done by qualified professionals.

DURING A STORM/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. Bridges may be washed out, and culverts overtopped. Do not cross flooding streams...Turn Around, Don't Drown! Embankments along roadsides are particularly susceptible to landslides. Watch the road for collapsed pavement, mud, fallen rocks, and other indications of possible debris flows. Be aware that strong shaking from earthquakes can induce or intensify the effects of landslides.

AFTER A LANDSLIDE: Stay away from the slide area. There may be danger of additional slides. Check for injured and trapped persons near the slide area. Give first aid if trained. Remember to help your neighbors who may require special assistance-infants, elderly people, and people with disabilities. Listen to a battery-operated radio or television for the latest emergency information. Remember that flooding may occur after a mudflow or a landslide. Check for damaged utility lines. Report any damage to the utility company. Check the building foundation, chimney, and surrounding land for damage. Replant damaged ground as soon as possible since erosion caused by loss of ground cover can lead to flash flooding. Seek the advice of geotechnical expert for evaluating landslide hazards or designing corrective techniques to reduce landslide risk.

Lesson Plan: Here is a great lesson plan on erosion and landslides.

Lesson Plan: Here is a great lesson plan on landslides for grades 6-8.

Lesson Plan: This lesson consists of landslides, liquefaction, and structural failure caused by earthquakes.

Science Fair Project Ideas: Here is a complete list of science fair project ideas. Discover the science behind the weather that impacts us every day.

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What is a landslide? A landslide is defined as the movement of a mass of rock, debris, or earth down a slope due to gravity. The materials may move by falling, toppling, sliding, spreading, or flowing. What causes a landslide? Almost every landslide has multiple causes.

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A landslide is the movement of rock, earth, or debris down a sloped section of land. Landslides are caused by rain, earthquakes, volcanoes, or other factors that make the slope unstable. Geologists, scientists who study the physical formations of the Earth, sometimes describe landslides as one type of mass wasting. A mass wasting is any downward movement in which the Earth's surface is worn away. Other types of mass wasting include rockfalls and the flow of shore deposits called alluvium. Near populated areas, landslides present major hazards to people and property. Landslides cause an estimated 25 to 50 deaths and $3.5 billion in damage each year in the United States.

What Causes Landslides?

Landslides have three major causes: geology, morphology, and human activity.

Geology refers to characteristics of the material itself. The earth or rock might be weak or fractured, or different layers may have different strengths and stiffness.

Morphology refers to the structure of the land. For example, slopes that lose their vegetation to fire or drought are more vulnerable to landslides. Vegetation holds soil in place, and without the root systems of trees, bushes, and other plants, the land is more likely to slide away.

A classic morphological cause of landslides is erosion, or weakening of earth due to water. In April 1983, the town of Thistle, Utah, experienced a devastating landslide brought on by heavy rains and rapidly melting snow. A mass of earth eventually totaling 305 meters wide, 61 meters thick, and 1.6 kilometers long (1,000 feet wide, 200 feet thick, and one mile long) slid across the nearby Spanish Fork River, damming it and severing railroad and highway lines. The landslide was the costliest in U.S. history, causing over $400 million in damage and destroying Thistle, which remains an evacuated ghost town today.

Human activity, such as agriculture and construction, can increase the risk of a landslide. Irrigation, deforestation, excavation, and water leakage are some of the common activities that can help destabilize, or weaken, a slope.

Types of Landslides

There are many ways to describe a landslide. The nature of a landslide's movement and the type of material involved are two of the most common.
Landslide Movement
There are several ways of describing how a landslide moves. These include falls, topples, translational slides, lateral spreads, and flows. In falls and topples, heavy blocks of material fall after separating from a very steep slope or cliff. Boulders tumbling down a slope would be a fall or topple. In translational slides, surface material is separated from the more stable underlying layer of a slope. An earthquake may shake the loosen top layer of soil from the harder earth beneath in this type of landslide. A lateral spread or flow is the movement of material sideways, or laterally. This happens when a powerful force, such as an earthquake, makes the ground move quickly, like a liquid.
Landslide Material
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 lahars, are among the most devastating type of landslides. The largest landslide in recorded history took place after the 1980 eruption of Mount St. Helens in the U.S. state of Washington. The resulting flow of ash, rock, soil, vegetation and water, with a volume of about 2.9 cubic kilometers (0.7 cubic miles), covered an area of 62 square kilometers (24 square miles).
Other Factors
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 expelled by volcanoes. Some landslides, called mudslides, contain a high amount of water and move very quickly. Complex landslides consist of a combination of different material or movement types.

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A landslide is the movement of rock, earth, or debris down a sloped section of land.

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Rain is pouring hard and fast-more than eight inches in just an hour, turning river water brown with mud. Earthworms wiggle up to the ground as the soil becomes too wet for them. A flood might be coming.

Just about any place on Earth can experience flooding. When so much rain falls that the ground can't absorb it or waterways can't hold it, the overflowing water becomes a destructive force. In the United States, flooding causes more death and damage than tornadoes, hurricanes, or lightning.

How floods develop

During a rainstorm, precipitation-or the water that comes from rain or snow-goes to different places. Some of it flows into streams, lakes, or city water systems. Other precipitation evaporates and returns to the atmosphere.

But much of the rainwater is absorbed by soil. It flows through the top layer of the ground, to plant roots below the surface. This helps provides plants with the water and nutrients they need to grow. The excess water moves deeper into the ground through layers of dirt and rocks where until it becomes part of natural underground wells called groundwater.

A habitat can naturally absorb a healthy amount of rainfall it needs to thrive. But too much rain can cause lake and river levels to rise and overflow their banks, or the soil to become too wet to absorb more water. And though you might think extremely dry habitats would welcome too much rain, it turns out that the parched dirt can't absorb the rain fast enough to capture it all.

Severe coastal storms, quickly melting ice and snow, and collapsed barriers (like concrete dams) can also cause floods. Even damaged beaver dams can lead to an overflow of water that the surrounding earth can't absorb.

Different types of floods

Floods can form slowly over several days or overwhelm an area with little warning. How quickly a flood forms often depends on the habitat.

Slow-forming river flooding happens in regions called floodplains. These are large, flat areas of land along waterways with very shallow banks. When big storms hit, the water overflows the banks and spreads out across the plains.

This type of flooding isn't always bad. It brings nutrients to the surrounding soil, making it fertile for growing crops. That's why many people live in or near floodplains.

But too much water can destroy crops and damage homes. Rushing water can disrupt ecosystems by moving aquatic plants and animals to other habitats. And if flooding is so severe that it flows into local water treatment facilities, experts must monitor the incoming water to make sure the water is safe.

Another type of flooding is called a flash flood, when a flood happens within six hours of a heavy rainfall-as much as eight inches an hour. With no place to go, the moving water will tear through highways, valleys, and canyons, washing away vehicles, roads, bridges, and houses.

Quickly melting ice and snow can also cause flash flooding, especially when mountain snowmelt overflows the waterways below. On coastlines, hurricane rains cause water levels to rise, and the high winds push that water onto land. Called a storm surge, this also causes flash flooding.

Flooding in the future

Scientists believe that warming temperatures caused by climate change are increasing the risk of floods all over the world, especially in coastal and low-lying areas.

Warmer water changes the patterns of ocean currents, which changes global weather patterns. This means that some places will receive more rainfall than the ground can absorb. Other places will get less rain so the land will be drier-and unable to handle rainfall when it does occur.

Scientists think that climate change could also cause stronger hurricanes, with more rain and higher winds causing bigger storm surges. A warmer climate could also mean more snowmelt overwhelming the soil; melting polar ice could cause sea levels to rise and increase flooding. ( Find out how you can help slow climate change.)

How to survive a flood

Experts might issue a flash flood watch if weather conditions are right. It doesn't mean flooding will happen but that meteorologists want people to be prepared. When experts are sure a flash flood is on the way, they issue a warning so people can evacuate immediately. Here's how to keep you and your family safe.

Before a flood
* Know your neighborhood. Research how close you are to streams, drainage channels, canyons, and any other low-lying areas that might flood.
* Keep emergency contact phone numbers in one place so you can get in touch with family members.
* Put together an evacuation plan and share it with everyone in your household. Know what paths and routes you can use to quickly get to a high, dry place.
* Conduct flood drills to practice evacuating quickly.
* Maintain an emergency kit with a three-day supply of food and water. Experts recommend canned or dried foods that don't need to be cooked, and at least one gallon of water per day for each person and pet.

During a flood
* Never wait for orders to leave; if you think a flood might be coming, evacuate immediately.
* If flooding hasn't started, move important items to upper floors of your house.
* If flooding has already started where you are, move to the highest place you can find, like a roof of a house or car. Bring as much food, water, and sheltering blankets as possible.
* Never walk through flood water, especially if it's moving. Hazardous chemicals, sewage, and even wild animals are often in floodwater, and just six inches of moving water can knock you off your feet.
* If you must walk through water to escape, walk where the water is still. Never touch electrical equipment if you are standing in water, or even if you're wet.
* If water is quickly rising while you're in your car, leave your vehicle and move to higher ground, like a hill or bridge.

After a flood
* If you've evacuated your house, return only after you're given the all-clear from officials.
* If you stayed put, check your house for damage to electrical systems and appliances. Get rid of any food that might be contaminated from floodwater (or because it's been unrefrigerated for awhile).
* Check your home for wild animals, especially snakes. They can get washed into your home with the floodwater.
* Ask an adult before you use water to brush your teeth, make food, or even wash your hands. Flooding can contaminate water and make you sick.
Learn more about floods at National Geographic.
Flood safety tips from the Nat Geo Kids book Extreme Weather by Thomas Kostigen

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Learn about what causes flooding, different types of floods-and how to stay safe.

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23 Interesting Flood Facts for Kids (2023 Updated)

A flood is a water level rise that has nowhere to go. Floods can range in depth from a few inches to many feet. Floodwater has a tremendous and deadly force. Heavy rain can transform a brook just ankle-deep into an uncontrollable 30-foot-high tsunami that overwhelms everything in its path in less than an hour. Flooding is fatal regardless of how quickly it occurs or what causes it.

In this article, we will find out some interesting facts about floods for kids and what causes them, so keep on reading to learn more.

Floods are destructive

In comparison to other severe weather-related catastrophes, floods inflict more deaths and property damage. Many people perish while trying to drive or walk through a flooded area. Six inches of running water is more than enough to cause someone to lose their balance. In just two feet of water, an automobile can lose its balance.

The most frequent natural and human causes of floods are:

Heavy rains: Flooding can be explained most simply by heavy rains. Water doesn't drain nearly as rapidly as it should when it rains. In other words, the drainage systems become clogged, and water rises, occasionally into houses.

Concrete urban drainage basins: There is no ground for water to sink into when using a concrete urban drainage basin. As a result, low-lying areas will flood when those drainage basins are full.

Storm surges and tsunamis: Both storm surges are associated with hurricanes and other storms, and tsunamis, occasionally brought on by underwater earthquakes, can result in considerable flooding.

Channels with steep sides: When there is rapid runoff into lakes, rivers, and other reservoirs, flooding happens frequently, which often occurs in rivers and other channels with steep slopes.

Overflowing rivers: If you reside near a river and locations upstream suffer severe rains, this could cause a significant overflow where you live.

Broken dams: Since a large portion of America's infrastructure was constructed in the 20th century, it is aging. Aging dams may crumble and release torrents of water on careless homes when heavy rains and rising water levels occur.

Lack of vegetation: Lack of vegetation, on the other hand, does little to prevent water from draining, which might result in flash flooding.

Snowmelt: A winter with a lot of snow and other precipitation can cause spring flooding. After all, they must go somewhere when the snow and ice melt.

Types of floods:

River flood: A flood in a river happens when the water rises above the riverbanks. Every river and stream, especially larger ones that flood every two years, can potentially flood. Extreme rainfall from tropical storm systems, persistent thunderstorms, combined rainfall and snowmelt, and ice jams are frequently blamed for river flooding. These bursts of melting snow or rain raise water levels above riverbanks and flood nearby areas.

Groundwater flood: Flooding from underground water is known as a groundwater flood, and it happens when there is a lot of rain in urban and rural regions. They may last for weeks or months before the Earth can absorb the standing water, which makes them problematic. As a result, they increase the risk of long-term health issues like mold and severely damaged properties.

Coastal flood: A coastal flood is an accumulation of water on land brought on by storm surges, high winds, or waves. Coastal communities are susceptible to flooding because of their proximity to the water, and the threat is expected to increase due to climate change. Most Americans-roughly 50%-live in coastal regions, with Florida, Louisiana, California, New Jersey, and New York among the states most susceptible to coastal flooding.

Flash flood: The deadliest type of flooding is a flash flood. They are brought on by a broken dam or a sudden downpour of severe rain. People may be caught up in them before they have a chance to flee since they take place so swiftly. Flash floods frequently happen in steep areas or near dry riverbeds. A dry riverbed can fill up in a flash flood in minutes. Flash floods can bring walls of water up to 20 feet high.

Sewage flood: Sewage flooding is brought on by sudden, intense rainfall that overwhelms sewage pipes or treatment facilities. The most uncomfortable floods are caused by sewage leaks from pipes, drains, toilets, sinks, or showers. In these circumstances, professionals' quick response and in-depth clean-up are essential.

Interesting Flood facts for kids:

Floods can be extremely powerful sometimes.

It takes only six inches of swift water to bring someone to the ground. Avoid attempting to cross flooded areas on foot. Frequently, the water is deeper than you think and may be contaminated or contain harmful debris.

Drivers navigating too-deep water account for 66% of flood-related fatalities. Never attempt to drive through the water if you are unsure of its depth. A little car can be carried away by 12 inches of water, and most vehicles can be carried away by two feet.

Floods can sometimes be helpful also.

Floods are not always bad, though. People have always constructed their towns by rivers because they need water for farming and drinking. Occasionally, muddy flood waters leave behind a covering of rich, damp soil. Ancient Egyptians relied on the Nile River 's annual flooding to aid their crops' growth.

Floods can carry harmful chemicals.

Go to the highest floor or ground you can find safe during a flood. Make sure to cleanse your skin with soap and sterilized water if it comes in contact with floodwater because you don't know what all substances could be there in the water.

Floods make wetlands act as sponges.

After the peak flood surges, wetlands operate as natural sponges, holding and gradually releasing floods. A single acre of wetland can hold 330,000 gallons of water when saturated to a depth of one foot, enough to flood thirteen average-sized homes thigh-deep.

People living in Flood-prone areas require regular stocks of essential items.

If you live in a flood-prone area, it is essential to stock up on items for personal hygiene, non-perishable foods, 3 gallons of water per person for three days, a battery-operated radio for weather reports, extra batteries, and first aid supplies.

Floods can create other disasters, too, so you should always take them seriously.

Aside from wildfires, floods are the natural calamity that occurs most frequently. 90% of all-natural disasters in the United States that the President has declared involve flooding. The fact that there are more floods than other natural disasters is one factor in this, but another is that people don't take floods seriously.

Floodplains are extremely important.

Even though they make up only 2% of the Earth's land surface, floodplains contribute about 25% of all benefits from ecosystem services dependent on the land. Low-lying areas that frequently flood naturally surround rivers and other water bodies known as floodplains. Floodplains are considered the "lifeblood" of the surrounding areas due to their regular flooding.

Increasing flood losses are a major problem.

Despite spending billions on flood protection, there were more floods, and average annual flood losses rose from $6 billion to $10 billion in the first decade of the new century due to heavy rainfall events and changes in land use.

In case of extreme flooding, we could also experience a food shortage at some point.

Over 25% of flood insurance claims made under the National Flood Insurance Program (NFIP) are for buildings outside of high-risk floodplains, according to the Federal Emergency Management Agency (FEMA). Whether in a floodplain or not, everyone in the country is at risk of flooding.

Did you know about the worst flood ever?

The 1931 Yangtze-Huai River floods, also known as the floods in 1939 China, were the deadliest flood on record. According to some estimates, four million people have died. Additionally, this flood is regarded as the worst deadly natural disaster in recorded history.

Conclusion

We hope you learned something interesting from the above-mentioned flood facts for kids. If you're interested in more facts about some other natural disasters, visit our website.

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23 Interesting Flood Facts for Kids ([year] Updated)

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23 Interesting Flood Facts for Kids ( Updated) A flood is a water level rise that has nowhere to go. Floods can range in depth from a few inches to many feet. Floodwater has a

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Nourishment is not a long-term solution to beach erosion. The erosive forces of waves, storms, and rising sea levels do not disappear after nourishment takes place. Waves will continue to "chew on" the sand, and eventually it erodes away, moving down the coast and offshore.

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A seawall (or sea wall) is a form of coastal defence constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a sea wall is to protect areas of human habitation, conservation and leisure activities from the action of tides, waves, or tsunamis. As a seawall is a static feature it will conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea. The shoreline is part of the coastal interface which is exposed to a wide range of erosional processes arising from flowing water sources, wind and terrestrial sources, meaning that a combination of denudational processes will work against a seawall.

The coast is generally a high-energy, dynamic environment with spatial variations over a wide range of timescales. The coast is exposed to erosion by rivers and winds as well as the sea, so that a combination of denudational processes will work against a sea wall. Because of these persistent natural forces, sea walls need to be maintained (and eventually replaced) to maintain their effectiveness.

The many types of sea wall in use today reflect both the varying physical forces they are designed to withstand, and location specific aspects, such as local climate, coastal position, wave regime (determined by wave characteristics and effectors), and value (morphological characteristics) of landform. Sea walls are hard engineering shore-based structures which protect the coast from erosion. But various environmental problems and issues may arise from the construction of a sea wall, including disrupting sediment movement and transport patterns. Combined with a high construction cost, this has led to an increasing use of other soft engineering coastal management options such as beach replenishment.

Sea walls may be constructed from various materials, most commonly reinforced concrete, boulders, steel, or gabions. Other possible construction materials are: vinyl, wood, aluminium, fibreglass composite, and large biodegrable sandbags made of jute and coir. In the UK, sea wall also refers to an earthen bank used to create a polder, or a dike construction. The type of material used for construction is hypothesized to affect the settlement of coastal organisms, although the precise mechanism has yet to be identified.

A seawall works by reflecting incident wave energy back into the sea, thus reducing the energy available to cause erosion. Sea walls have two specific weaknesses. First, wave reflection from the wall may result in hydrodynamic scour and subsequent lowering of the sand level of the fronting beach. Second, sea walls may accelerate erosion of adjacent, unprotected coastal areas because they affect the littoral drift process.

Different designs of man-made tsunami barriers include building reefs and forests to above-ground and submerged seawalls. In 2005, India began planting Casuarina and coconut saplings on its coast as a natural barrier against future tsunamis like the 2004 Indian Ocean earthquake. Studies have found that an offshore tsunami wall could reduce tsunami wave heights by up to 83%.

The design and type of sea wall that is appropriate depends on aspects specific to the location, including the surrounding erosion processes. There are three main types of seawalls: vertical, curved or stepped, and mounds, as set out in the table:

Images for kids

A seawall, made of rocks in Paravur near Kollam city in India.

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We should stop planting betelnut trees.

We should use seawalls.

We should use beach nourishment.