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NASA explains the ingredients needed for hurricanes.

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Wildfires: How they form, and why they're so dangerous

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Wildfires: How they form, and why they're so dangerous

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Newsela | Wildfires: How they form, and why they're so dangerous

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Many wildfires are started by people. But drought, dry weather, strong winds and even lightning can turn a spark into a devastating months-long blaze.

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How tornadoes form and why they're so unpredictable

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How tornadoes form and why they're so unpredictable

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Newsela | How tornadoes form and why they're so unpredictable

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What does it take for a tornado to form?

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Floods often destroy homes and devastate crops and wildlife habitat. Severe floods can even kill people and animals. Floods also have benefits: they replenish groundwater and enrich soil.

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10 Facts About Flooding - American Rivers

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10 Facts About Flooding - American Rivers

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1 - FLOODS ARE THE MOST COMMON NATURAL HAZARDS IN THE UNITED STATES

In terms of number of lives lost and property damage, flooding is the most common natural hazard. Floods can occur at any time of the year, in any part of the country, and at any time of the day or night. While heavy precipitation is the common cause of flooding, hurricanes, winter storms and snowmelt are common, but often overlooked, causes of flooding.

2 - Floodplains provide roughly 25 percent of all land-based ecosystem service benefits yet they represent just 2 percent of Earth's land surface

Floodplains are the low lying areas that surround rivers and other water bodies naturally flood on a frequent basis. Naturally frequent flooding makes floodplains the "lifeblood" to surrounding areas.

They provide clean water and wildlife habitat among many other benefits including one of the most visible functions, the ability to store large volumes of flood water and slowly release these waters over time.

3 - Wetlands in the U.S. save more than $30 billion in annual flood damage repair costs

Wetlands act as natural sponges, storing and slowly releasing floodwaters after peak flood flows have passed. A single acre of wetland, saturated to a depth of one foot, will retain 330,000 gallons of water - enough to flood thirteen average-sized homes thigh-deep.

4 - Over the past century, we have experienced more intense and frequent storms

Over the last 50 years, Americans have seen a 20% increase in the heaviest downpours. With a changing climate, we know that the size of the nation's floodplains will grow by 40 to 45% over the next 90 years, putting more people in harm's way.

5 - Damages from flood losses have increased to an average $10 billion per year

In the first decade of the new millennium, extreme rainfall events combined with changes in land use have resulted in an increase in floods and an increase in annual average flood losses from $6 billion to $10 billion despite the billions of dollars invested in flood control.

6 - In 2011 alone, there were 58 Federal flood disaster declarations, costing over $8 billion and caused 113 deaths, both exceeded the 30-year averages.

A homeowner with a 30-year mortgage in a 100-year flood area has a 1 in 4 chance that such a flood will occur and more than double the chance of being damaged by a flood than by a fire.
Floods can happen everywhere, it just depends on whether the risk is high, medium, or low: people outside of "high-risk" areas (or the "100-year" floodplain) actually file over 20% of the flood insurance claims and receive one-third of disaster assistance for flooding.

7 - Roughly 17% of all the urban land in the United States is located in the "100-year" or high risk flood zone

If you live in a high-risk area and you have a federally backed mortgage, you must buy flood insurance. While flood insurance costs vary, flood insurance averages $600 a year. However, if your community participates in FEMA's voluntary Community Rating System (CRS), you can receive up to 45% off your insurance premium.

8 - Over the course of a 30 year mortgage, homeowners in the 100-year floodplain have a 1 in 4 chance or greater of being flooded - twice the probability of fire damage

Floods are not limited to the 100-year floodplain and 100 year floods can happen more frequently than once every century. Over 20% of the flood insurance claims and one-third of all flood disaster assistance is for flood damage outside the 100-year floodplain. The concept of a 100-year flood is a statistical projection that refers to a flood event that has a 1 percent probability of occurring each and every year. As the climate changes, the size and area subject to the 100-year flood will increase.

9 - Flood mitigation practices that reduce the loss of life and damages to properties provide $5 in benefits for every dollar invested

When homeowners take steps to protect themselves and to reduce the impacts of flooding through mitigation practices such as elevating or flood-proofing their homes, moving out of harm's way, and investing in "natural defenses" they can save themselves and taxpayer's money because it's less expensive to prepare for a flood than it is to keep cleaning up afterwards.

10 - Levees can and do fail often with catastrophic consequences

The good news is there are proven methods to restore and reconnect our rivers. Setting levees back or otherwise modifying levees allows the floodplain to store more water naturally, keep people safe, and provide other benefits such as clean water and wildlife habitat.

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1 - FLOODS ARE THE MOST COMMON NATURAL HAZARDS IN THE UNITED STATES In terms of number of lives lost and property damage, flooding is the most common natural hazard. Floods can occur at any time of the year, in any part of the country, and at any time of the day or night.

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A flood is an overflow of water on normally dry ground. This is most commonly due to an overflowing river, a dam break, snowmelt, or heavy rainfall. Less commonly happening are tsunamis, storm surge.

The most deadly flooding was in 1931 in China and killed between 2,000,000 and 4,000,000 people. The Kerala flood in India was another flood that has destroyed people's houses.

During a flood, people try to move themselves and their most precious belongings to higher ground quickly. The process of leaving homes in search of a safe place is called flood evacuation.

Bangladesh is the most flood prone area in the world.

Pollution of drinking water

During a flood there is plenty of water logging and overflow of water, but it is mostly polluted and not safe to drink. If people drink this dirty water, they may suffer from diseases such as typhoid and cholera, hepatitis and other such diseases. People can get ready to survive a flood by filling many containers with fresh and clean drinking water and storing other emergency supplies; like: medicine and food. During flood people try to go to higher sides because the flood water wouldn't reach high areas. Also drains overflow and mix with clean water and people who drink it might fall ill.

Floods can happen on flat or low-lying areas when water is supplied by rainfall or snowmelt more rapidly than it can either infiltrate or run off. The excess accumulates in place, sometimes to hazardous depths. Surface soil can become saturated, which effectively stops infiltration, where the water table is shallow, such as a floodplain, or from intense rain from one or a series of storms. Infiltration also is slow to negligible through frozen ground, rock, concrete, paving, or roofs. Areal flooding begins in flat areas like floodplains and in local depressions not connected to a stream channel, because the velocity of overland flow depends on the surface slope. Endorheic basins may experience areal flooding during periods when precipitation exceeds evaporation.

Riverine (Channel)

Floods occur in all types of river and stream channels, from the smallest ephemeral streams in humid zones to normally-dry channels in arid climates to the world's largest rivers. When overland flow occurs on tilled fields, it can result in a muddy flood where sediments are picked up by run off and carried as suspended matter or bed load. Localized flooding may be caused or exacerbated by drainage obstructions such as landslides, ice, debris, or beaver dams.

Slow-rising floods most commonly occur in large rivers with large catchment areas. The increase in flow may be the result of sustained rainfall, rapid snow melt, monsoons, or tropical cyclones. However, large rivers may have rapid flooding events in areas with dry climate, since they may have large basins but small river channels and rainfall can be very intense in smaller areas of those basins.

Rapid flooding events, including flash floods, more often occur on smaller rivers, rivers with steep valleys, rivers that flow for much of their length over impermeable terrain, or normally-dry channels. The cause may be localized convective precipitation (intense thunderstorms) or sudden release from an upstream impoundment created behind a dam, landslide, or glacier.

Flash floods are the most common flood type in normally-dry channels in arid zones, known as arroyos in the southwest United States and many other names elsewhere. In that setting, the first flood water to arrive is depleted as it wets the sandy stream bed. The leading edge of the flood thus advances more slowly than later and higher flows. As a result, the rising limb of the hydrograph becomes ever quicker as the flood moves downstream, until the flow rate is so great that the depletion by wetting soil becomes insignificant.

Estuarine and coastal

Flooding in estuaries is commonly caused by a combination of storm surges caused by winds and low barometric pressure and large waves meeting high upstream river flows.

Coastal areas may be flooded by storm surges combining with high tides and large wave events at sea, resulting in waves over-topping flood defenses or in severe cases by tsunami or tropical cyclones. A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category. Research from the NHC (National Hurricane Center) explains: "Storm surge is an additional rise of water generated by a storm, over and above the predicted astronomical tides. Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide. This rise in water level can cause extreme flooding in coastal areas particularly when storm surge coincides with spring tide, resulting in storm tides reaching up to 20 feet or more in some cases."

Urban flooding

Catastrophic

Catastrophic riverine flooding is usually associated with major infrastructure failures such as the collapse of a dam, but they may also be caused by drainage channel modification from a landslide, earthquake or volcanic eruption. Examples include outburst floods and lahars. Tsunamis can cause catastrophic coastal flooding, most commonly resulting from undersea earthquakes.

Causes of floods

Flooding is usually caused when a volume of water within a water body, such as a lake, overflows outside it. Sometimes if a dam breaks, it suddenly releases a large amount of water. The result is that some of the water travels to land, and 'floods' the area. Many rivers are in a channel, between river banks. They flood when the strength of the river causes it to flow beyond the banks. This is more common at bends or meanders.

Flood damage can be prevented by moving away from places that flood. However, people have long liked to have their homes and businesses alongside water because water is good for agriculture and transport and in other ways. Floods are also caused due to improper management of drains.

Rainfall is the most common cause. Snow melt is also a cause of flooding. Tsunamis and Storm Surge are less common ways that floods happen. Coastal Flooding is another common cause of flooding, and this is caused by low pressure systems or storms.

Flood safety planning

In the United States, the National Weather Service gives out the advice "Turn Around, Don't Drown" for floods; that is, it recommends that people get out of the area of a flood, rather than trying to cross it. At the most basic level, the best defense against floods is to seek higher ground for high-value uses while balancing the foreseeable risks with the benefits of occupying flood hazard zones. Critical community-safety facilities, such as hospitals, emergency-operations centers, and police, fire, and rescue services, should be built in areas least at risk of flooding. Structures, such as bridges, that must unavoidably be in flood hazard areas should be designed to withstand flooding. Areas most at risk for flooding could be put to valuable uses that could be abandoned temporarily as people retreat to safer areas when a flood is imminent.

Planning for flood safety involves many aspects of analysis and engineering, including:

observation of previous and present flood heights and inundated areas,

statistical, hydrologic, and hydraulic model analyses,

mapping inundated areas and flood heights for future flood scenarios,

long-term land use planning and regulation,

engineering design and construction of structures to control or withstand flooding,

intermediate-term monitoring, forecasting, and emergency-response planning, and

short-term monitoring, warning, and response operations.

Each topic presents distinct yet related questions with varying scope and scale in time, space, and the people involved. Attempts to understand and manage the mechanisms at work in floodplains have been made for at least six millennia.

In the United States, the Association of State Floodplain Managers works to promote education, policies, and activities that mitigate current and future losses, costs, and human suffering caused by flooding and to protect the natural and beneficial functions of floodplains - all without causing adverse impacts. A portfolio of best practice examples for disaster mitigation in the United States is available from the Federal Emergency Management Agency.

In many countries around the world, waterways prone to floods are often carefully managed. Defenses such as detention basins, levees, bunds, reservoirs, and weirs are used to prevent waterways from overflowing their banks. When these defenses fail, emergency measures such as sandbags or portable inflatable tubes are often used to try to stem flooding. Coastal flooding has been addressed in portions of Europe and the Americas with coastal defenses, such as sea walls, beach nourishment, and barrier islands.

In the riparian zone near rivers and streams, erosion control measures can be taken to try to slow down or reverse the natural forces that cause many waterways to meander over long periods of time. Flood controls, such as dams, can be built and maintained over time to try to reduce the occurrence and severity of floods as well. In the United States, the U.S. Army Corps of Engineers maintains a network of such flood control dams.

In areas prone to urban flooding, one solution is the repair and expansion of man-made sewer systems and stormwater infrastructure. Another strategy is to reduce impervious surfaces in streets, parking lots and buildings through natural drainage channels, porous paving, and wetlands (collectively known as green infrastructure or sustainable urban drainage systems (SUDS)). Areas identified as flood-prone can be converted into parks and playgrounds that can tolerate occasional flooding. Ordinances can be adopted to require developers to retain stormwater on site and require buildings to be elevated, protected by floodwalls and levees, or designed to withstand temporary inundation. Property owners can also invest in solutions themselves, such as re-landscaping their property to take the flow of water away from their building and installing rain barrels, sump pumps, and check valves.

In some areas, the presence of certain species (such as beavers) can be beneficial for flood control reasons. Beavers build and maintain beaver dams which will reduce the height of flood waves moving down the river (during periods of heavy rains), and will reduce or eliminate damage to human structures, at the cost of minor flooding near the dams (often on farmland). Besides this, they also boost wildlife populations and filter pollutants (manure, fertilisers, slurry). UK environment minister Rebecca Pow stated that in the future the beavers could be considered a "public good" and landowners would be paid to have them on their land.

Related pages

Images for kids

A dog sitting on top of 2 feet of mud deposited by flooding in the 2018 Kerala floods in India. Flooding not only creates water damage, but can also deposit large amounts of sediment.

Minor flooding in a parking lot off Juniper street Atlanta on Christmas Eve from thunderstorms caused by an El Nino event. The same El Nino caused recorded highs for January in Atlanta

Flash flooding caused by heavy rain falling in a short amount of time.

Dozens of villages were inundated when rain pushed the rivers of northwestern Bangladesh over their banks in early October 2005. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured the top image of the flooded Ghaghat and Atrai Rivers on October 12, 2005. The deep blue of the rivers is spread across the countryside in the flood image.

In Spanish: Inundación para niños

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Flood Facts for Kids - Interesting Information about Floods

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Flood Facts for Kids - Interesting Information about Floods

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Flood Facts For Kids

Check out our flood facts for kids and learn a range of interesting information about floods.

Did you know that floods can be an important natural process for farming? Understand how floods happen, the different types of flood events and much more with our flood facts for kids.

Depending on their type, floods can develop very slowly over time after extensive rains or in just a few minutes, very quickly, without any sign of rain.

There are many types and ways floods can occur, including, due to overflowing rivers, due to extreme coastal events, by natural or artificial ground saturation from excess rainfall, or by catastrophic failure in infrastructure.

Flash floods are extreme versions of a river flooding event. They can occur very quickly, often without warning and with little or no excessive rainfall. Flash floods are the result of a river blockage either natural or artificial (such as a landslide, glacier, or dam) giving way and releasing a massive amount of built up water.

Areal or urban flooding occurs when low-lying impenetrable ground becomes saturated as rainfall cannot run off as quickly as the accumulation of water. For example, on natural drought hardened or frozen farmland, or on concrete paving.

Floods can damage bridges, roads and other transport links. Infrastructure such as buildings, cars and houses can be left saturated or completely taken by the waters. While sewage systems and power grids can be destroyed.

After floodwaters recede, land can be contaminated with hazardous material, such as building debris, fuel and untreated sewage. Residents are often left without power or clean drinking water which can lead to outbreaks of diseases.

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Flood Facts for Kids - Interesting Information about Floods

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Flood Facts For Kids Check out our flood facts for kids and learn a range of interesting information about floods. Did you know that floods can be an important natural process for farming? Understand how floods happen, the different types of flood events and much more with our flood facts for kids.

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A dark greenish tinge covers the sky, and black storm clouds threaten above. The wind roars loudly while cats hide under couches and dogs start howling. A tornado is forming.

Also known as twisters, tornadoes are violently spinning, funnel-shaped columns of air that stretch from the dark thunderclouds they form in all the way to the ground. The wind from a tornado can top 250 miles an hour-that's faster than a race car! These extreme gusts can rip apart buildings, destroy bridges, flip trains, and send cars flying. They can even tear the bark off trees and suck all the water from a riverbed.

Tornadoes occur all over the planet, but the United States leads the world in the strength and number of storms: About a thousand twisters touch down every year. ( Argentina and Bangladesh are next.) As part of larger U.S. storm systems, they cause about 80 deaths a year and close to $1 billion in damage.

How tornadoes develop

Thunderstorms form when cold, dry air is pushed over warm, humid air. When that warm air rises through the colder air, it causes an updraft, or a change in wind direction.

If winds from the thunderstorm vary greatly in speed or direction, the updraft will begin to rotate. As the rotating updraft draws in more warm air from the moving thunderstorm, its rotation speed increases, and a funnel cloud begins to form. As the twister gains strength, the funnel becomes longer. (The funnel becomes more visible as more dirt and debris is caught in its rotation.) It's most dangerous when it touches the ground.

The most violent tornadoes come from supercells-the name scientists give to large thunderstorms with winds already in rotation. About one in a thousand thunderstorms becomes a supercell, and one in five or six supercells creates a tornado.

For all their power, the average tornado lasts only about 10 minutes, though some can rage for over an hour. Twisters usually die when they move over colder ground or when the clouds above it start to break up.

The Tri-State Tornado of 1925 holds the record for time and distance of a tornado. Named for the three states it hit- Missouri, Illinois, and Indiana -the tornado took three and a half hours to tear through 219 miles.

Where and when tornadoes form

Although tornadoes have been spotted in every U.S. state, many form in a region called Tornado Alley. This zone in the Midwest extends from Texas to Ohio and includes Iowa, Kansas, South Dakota, Oklahoma, and Nebraska.

These states are in the path of warm, moist air traveling from the Gulf of Mexico as well as cool air blowing from the Rocky Mountains. When the warm and cool airstreams meet, tornadoes are likely to form.

Though the storms can happen at any time of the year, tornado season in Texas, Oklahoma, and Kansas occurs in May through early June. In North and South Dakota, Nebraska, Iowa, and Minnesota, tornadoes are more likely to form in June or July.

Tracking tornadoes

During thunderstorms, meteorologists use weather satellites, weather balloons, and buoys to gather data like wind speed and temperature. Then they analyze that data with supercomputers. This helps scientists pinpoint where and when a twister might form, as well as how strong or long-lasting it might be.

If weather conditions are right for a tornado to form, experts issue a tornado watch for a region, like a county or large part of a state. This doesn't mean that a tornado is on the way. But it could be-meteorologists issue the watch so people can be prepared.

When a tornado is spotted or picked up on weather radar, scientists issue a tornado warning for a smaller area, like a town or part of a city. People there are urged to take cover.

Some experts actually drive into areas where storms are forming! Vehicles tricked out with special science equipment measure things like temperature, humidity, and air pressure that's submitted to meteorologists at weather service headquarters. But the information that these "tornado chasers" gather also helps scientists better understand the science of tornados.

Thanks to these tools, meteorologists are now able to quickly predict when and where a tornado will form, giving people in a twister's path more time to seek shelter. For instance, in the 1980s, people only had about a five-minute warning before a tornado hit; by the late 2000s, the warning time grew to 13 minutes.

How to survive a tornado
Before a tornado
* Listen to weather reports for tornado warnings.
* Close all the windows.
* Prepare a safe room. This can be your basement or the lowest room in the center of your house or apartment building, away from outer walls and windows. Window-free closets and bathrooms work well, too.
* Fill the safe room with blankets, pillows, sleeping bags, and your family emergency kit (water, food, flashlight, and radio).
* Have an emergency safety plan. If you live in a trailer or mobile home, make sure you know where to go to evacuate.
During a tornado
* Stay inside-never attempt to watch or chase a tornado.
* Do not go near windows. It's not the tornado itself that causes most injuries; it's the flying debris-or the windows they crash through-that cause most injuries.
* Cover yourself with the pillows, blankets, and sleeping bags. If there's a sturdy piece of furniture, like a table, crawl under it.
* Cover your head and neck with your arms.
* If you're caught outside and can't find shelter, look for a ditch, gulley, or just a flat piece of ground away from trees and cars. Lie down as flat as you can and cover your head and neck with your arms. (Do not try this under a bridge or overpass.)
After a tornado
* Do not leave your shelter until local authorities give the OK. Follow their instructions.
* If you go outside, watch where you step-dangerous debris can be anywhere.
* Continue to monitor tornado reports. Sometimes more than one can whip up in the same place.
Learn more about tornadoes at National Geographic.
Tornado safety tips from the Nat Geo Kids book Extreme Weather by Thomas Kostigen and How to Survive Anything by Rachel Buchholz

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Find out what causes these deadly twisters-and how to stay safe.

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Have you ever heard of a fire triangle? Wildfires need three things to thrive and firefighters call these three things the fire triangle. They include a fuel source, such as dry wood and plants; oxygen, which is delivered by wind and air; and a heat source, such as a cigarette, a spark from a campfire, a lightning strike or even the sun.

Every year in the U.S., wildfires burn more than 5 million acres. Wildfires can start in a second and move at about 14 miles per hour.

Facts about Wildfires for Kids

Most wildfires are caused by humans, but some fires are caused by nature.

Wildfires can destroy homes and buildings and even kill people.

In some ways, wildfires are good, though. They clear dead and diseased plants so new plants can grow.

Firefighters sometimes fight wildfires from planes or helicopters. They drop water or fire-retardant chemicals on or near the fire.

Firefighters also fight wildfires by cutting back brush and grass.

In August 2018 California suffered the largest wildfire in the history of the state.

In the event of a wildfire it is important to be prepared. Call 911 and take the advice of the authorities. If an order is made to leave the area, do so immediately. Leave all personnel belongings, you can replace them.

Fill bathtubs and sinks with water and stay indoors with windows and doors closed but unlocked.

Keep away from windows.

If you happen to be caught outside in a wildfire keep low, try find a ditch and lie face down in it, covering your body. Try find an area clear from vegetation like trees and bushes.

If you happen to be in your vehicle, close the vents and windows. Lie on the floor again covering your body. If you can find an area free from vegetation its safer, stay there, do not panic. It is very easy to become disorientated in a wildfire, so driving around unsure where you are going will only put you in more danger.

Visit this government website and be prepared https://www.ready.gov/wildfires

Wildfires Vocabulary

Learn More All About Wildfires

This is the best video we found for kids to learn about Wildfires:

This is a video animation about preventing wildfires.

Wildfires Q&A

Question : What can I do to prevent wildfires?

Answer: Most wildfires happen during the heat of summer in dry, western states, such as Utah, Idaho, California and Colorado. If you live in one of these states, follow local rules about fires and fireworks. Be extra careful with campfires.

Enjoyed the Free Geography Kids online resources all about Wildfires info? Take the FREE & fun all about Wildfires quiz and download FREE all about Wildfires worksheet for kids. For lengthy info click here.

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All About Wildfires Fun Geography Facts for Kids. Learn more all about Wildfires with our best online kids science resource. Easy Earth Science for Kids.

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Learn what causes these deadly storms-and how to stay safe.

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Wildfire is a general term which includes forest fires, grassland fires, bushfires, brush fires and any other vegetation fire in countryside areas.

Wildfires occur in every continent except Antarctica. They can occur naturally and spontaneously, but many are caused by humans, accidentally or deliberately. Fossil records and human history show that wildfires do occur at intervals. The Great Oxygenation Event and the spread of land plants made Earth a planet of fire.

Wildfires can cause extensive damage to property and human life, but they also have some beneficial effects on wilderness areas. Some plant species depend on the effects of fire for growth and reproduction, although large wildfires may also have negative ecological effects.

Strategies of wildfire prevention, detection, and suppression have varied over the years. One of the more controversial methods is controlled burn: People permit or light small fires to burn away some of the fuel for a potential wildfire. While some wildfires burn in remote forested regions, they can cause extensive destruction of homes and other property in the zone between developed areas and undeveloped wilderness.

Plant adaptation

Plants in wildfire-prone ecosystems often have adaptations to their local conditions. Such adaptations include physical protection against heat, increased growth after a fire event, and flammable materials that encourage fire and eliminate competition. For example, plants of the genus Eucalyptus contain flammable oils that encourage fire and hard sclerophyll leaves that resist heat and drought. This makes them dominant over less fire-tolerant species. Dense bark, shedding lower branches, and high water content in external structures may also protect trees from rising temperatures. Fire-resistant seeds and reserve shoots that sprout after a fire encourage species preservation, as in 'pioneer' species that specialize in restarting ecological succession after a fire.

Smoke, charred wood, and heat can stimulate the germination of seeds. Smoke from burning plants promotes contains orange butenolide, which induces germination of seeds.

Grasslands in Western Sabah, Malaysian pine forests, and Indonesian Casuarina forests are believed to have resulted from previous periods of fire. The deadwood litter of Chamise (Californian greasewood shrub) is low in water content and flammable, and the shrub quickly sprouts after a fire. relies on periodic fires to reduce competition, release seeds from their cones, and clear the soil and canopy for new growth. Some have adapted to, and rely on, low-intensity surface fires for survival and growth. The optimum fire frequency for Caribbean pine in Bahamian pineyards is every 3 to 10 years. Too frequent fires favour herbaceous plants, and infrequent fires favour other tree species.

Related pages

Images for kids

In Spanish: Incendio forestal para niños

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Drought is a continuous period of dry weather when an area gets less than its normal amount of rain. Droughts can last months or even years. Because crops and other plants need water to grow and land animals need water to live, droughts can be dangerous. Because of the lack of water, famine occurs and sometimes deserts are created. Many people die every year in famines that are due to drought in subsistence farming areas. Sometimes conflicts can occur because of drought.

A drought is a natural event that is caused by other weather events like El Niño, high-pressure systems, and global warming. Drought can be triggered by people as well. Deforestation (people cutting down trees in forests and not replanting more trees), diverting (redirecting) rivers, and emptying lakes are ways that man interferes with nature and can cause drought.

It is often difficult to determine a specific time when a drought started because drought is a disaster that usually takes place slowly. Its effects often build up slowly over a long time and may last from months to years, even after rain resumes.

Causes of drought

Lack of Rain (precipitation)

Water can fall in three ways from the sky:

1. Water that falls as a liquid and stays a liquid,

2. Water that falls as a liquid and freezes when it touches the ground, and

3. Water that is already frozen and falls as ice.

Droughts occur mainly in areas where the normal levels of rainfall are already low. If it rains a little less than normal over time, a drought will happen. Wind can also be one of the factors in a drought when there is already a lack of rain. If a dry wind blows (like a wind from over the land) rather than a more humid wind (like a wind from over the ocean), it can dry the land faster.

In the tropics (the areas of the earth that are closest to the equator), there are distinct wet and dry seasons. During the wet seasons, the area becomes a Monsoon trough because monsoons are pulled into the movement of air. During the dry seasons, the Intertropical Convergence Zone ( Monsoon trough) moves dry air through the tropics. The movement of dry air eventually causes watering holes and rivers to dry up. This means that many grazing animals like zebras, elephants, and wildebeest are faced with a choice: move (migrate) to where there is water or die. The fruit and vegetable-bearing plants that are left ripen faster because evaporation and transpiration from the plants are increased. Bushfires are common during the dry season as well because of the lack of water in the remaining plants.

El Niño is a natural event that takes place when seawater temperature rises in the tropical Pacific Ocean. This changes the atmospheric pressure between the Pacific and Indian Oceans. Since atmospheric pressure determines weather, during El Niño we see drought in some areas of the world and heavy rainfall in other areas.

Erosion and human activities

Erosion is a process in which natural forces like wind, air, water, and gravity cause the earth to move or wear away. In dry, or arid, climates, the main source of erosion is the wind. Because the soil is already dry, wind can lift small particles and move them to another region. Particles that are suspended in the wind may rub against solid objects and cause erosion by abrasion. Wind erosion usually happens in areas where there is not enough rainfall to grow many plants.

Loess is a type of soil that is affected by wind erosion. It looks like little cliffs of sand and is common in the middle of the United States and other areas of the world like China, Hungary, and Belgium. Windbreaks (like large trees and bushes) are planted on and near loess to help block as much wind as possible.

Climate change

Scientists expect that because of global climate change, droughts will be triggered. Overall, they state that global warming will result in more rain falling all over the world, but areas that are prone to drought will increase as well. Some of the suggestions to fight global warming, however, involve the use of a space sunshade, which may also increase the chances of drought.

Types of drought

As drought continues, the conditions surrounding it gradually worsen and those living in drought areas are more affected. People define droughts in three main ways:

1. Meteorological drought happens when there is a prolonged time that an area receives less than its average precipitation. Meteorological drought usually comes before other kinds of drought.

2. Agricultural drought affects crop production or the ecology of a distinct area. This can happen because of poorly planned farming areas. The water that is available in the area has a hard time reaching the plants or erosion occurs. Meteorological drought conditions can affect agriculture as well.

3. Hydrological drought happens when the water in reserves like aquifers, lakes, and reservoirs drops below their normal amount. We see the effects of hydrological drought more slowly because it involves stored water that is used or moved but not refilled. This can be caused by people using or moving water or by a lack of rainfall.

Consequences of drought

The consequences of droughts and water shortages can be divided into three groups:

1. Environmental: Water levels drop and there is a lower flow of water. This lack of water is dangerous for animals that live in water. We see more pollution on the surface of the water. Wetlands dry out, causing more and larger fires. Wind erosion happens more easily, and plant life has a hard time surviving because of a lack of water, pests, and diseases. Animals have to move because of the lack of water and plants.

2. Economic: Farming is less successful during a drought, which means the price of groceries is affected because there is less food to sell. Livestock is more difficult to care for during a drought. Forests have fewer healthy trees and fewer animals. Energy production decreases in hydro plants (businesses that use water to make energy). Tourism even decreases because activities that involve water have a harder time working correctly.

3. Social: People's health can be affected by heat waves and having to use less water. People can become stressed due to higher food costs and the lack of other things that are normal in their life. Drought also results in snakes moving closer to water and food in residential areas resulting in more snake bites. Less-developed countries have more difficulties with water shortages because they do not have the same helpful equipment as more-developed countries. Sometimes they have to move because of pollution or lack of water. War can even break out because people or countries could begin fighting over food and water.

History of drought

Drought is a normal part of the cycle of the climate in most parts of the world. It is written about in the Epic of Gilgamesh and the Biblical story of Joseph. Historians believe that people migrated out of Chile and Africa thousands of years ago because of drought.

Well-known historical droughts include:

1900: a drought in India that killed between 250,000 and 3.25 million.

1921-22: drought in the Soviet Union in which over 5 million died from starvation

1928-30: a drought in Northwest China resulted in over 3 million deaths by famine.

1936 and 1941: droughts Sichuan Province China resulted in 5 million and 2.5 million deaths respectively.

The 1997-2009 Millennium Drought in Australia led to a water supply crisis across much of the country. As a result, many desalination plants were built for the first time.

In 2006, Sichuan Province, China, experienced its worst drought in modern times with nearly 8 million people and over 7 million cattle facing water shortages.

A 12-year drought that was devastating southwest Western Australia, southeast South Australia, Victoria, and northern Tasmania was "very severe and without historical precedent".

In 2005, the Amazon basin experienced its worst drought in 100 years.

Recurring droughts in East Africa have caused desert areas to grow. This is called desertification.

In 2012, a severe drought struck the western Sahel. 10 million people were at risk of famine and almost $1 billion was sent to help.

Protection, mitigation, and relief

Farmers can lessen the effects of (mitigate) drought by properly watering and rotating their crops. Agencies have been formed to focus on soil preservation. This began in 1935 after President Roosevelt signed documents creating the Soil Conservation Service. The name has since been changed to the Natural Resources Conservation Service.

Here is a list of ways that we can protect against drought, lessen the effects of drought, and bring relief to those who are affected by drought:

Cloud seeding: This is a form of purposely changing the weather to bring rainfall. This remains a hotly debated topic and there is not yet scientific proof that it would work.

Dams: Many dams and their associated reservoirs supply additional water in times of drought.

Desalination: Removing salt from seawater could make more fresh water available for watering plants and drinking.

Drought Monitoring: If we can closely watch and measure rainfall levels and compare them with current water usage, it could help prevent man-made drought.

Land use: Carefully planned crop rotation can help to minimize erosion and allow farmers to plant less water-dependent crops in drier years.

Outdoor water-use restriction: Regulating the use of sprinklers, hoses, or buckets for outdoor home maintenance can help prevent drought. In drier climates, it is popular to Xeriscape yards. Planning the landscaping in a way that requires little or no watering is a good way to preserve water.

Rainwater harvesting: We can collect and store water that is already given to us naturally. Rainwater from roofs or other surfaces can be used when we would normally use a hose.

Recycled water: Former wastewater (sewage) that has been treated and purified can be reused.

Transvasement: We can build canals or redirect rivers toward drought-prone areas.

Interesting facts about drought

Drought is a time when the land is too dry.

Drought can be caused by nature or by man.

When areas do not get enough rain, drought happens.

Weather patterns can bring about drought.

Erosion of soil can cause drought.

Humans can bring about drought by deforestation or using too much water.

Drought can have serious consequences: It can be bad for the environment and living things in certain areas, it can cause changes in the economy of an area or country, and it can affect the health of people.

There are many ways that people can help prevent drought and help areas that are naturally prone to drought.

Images for kids

Global drought total economic loss risk

Pair of dead oryx in Namibia during the 2018-19 Southern Africa drought.

In Spanish: Sequía para niños

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You feel the ground suddenly shake, and nearby objects are trembling. An earthquake is happening.

Also called a temblor, an earthquake is caused by the movement of parts of the Earth's crust, its outermost layer. They happen millions of times a year, but most are so small people don't even feel them.

But powerful earthquakes can cause landslides, tsunamis, flooding, and other dangerous events. Most damage and deaths happen in places where a lot of people live, because the shaking causes windows to break, structures to collapse, fire to break out, and other dangers.

Learn more about these unpredictable Earth tremors-and what to do if one rattles near you.

How earthquakes develop

The action all starts thousands of miles below your feet.

Picture Earth as a hard-boiled egg: Earth's core is the yolk, and the mantle is the white part. The outer crust is the eggshell.

People live on the surface of the crust. Below the surface-but still within the crust-are tectonic plates. Like gigantic puzzle pieces, these huge slabs of rock encircle the Earth. The seven major plates are named for the regions they rest under: the African, Antarctic, Eurasian, Indo-Australian, North American, Pacific, and South American tectonic plates

Tectonic plates aren't connected but are close together. Where they meet along their edges is called a fault. When heat from the Earth's core creates currents in the crust, the tectonic plates can scrape, bump, or drag along each other. This is what causes an earthquake-and why the surface sometimes cracks like an eggshell.

How to measure earthquakes

About a half-million quakes rock the Earth every day. Usually the quake is too small, too far below the surface, or too deep in the seafloor to be felt. Some, however, are so powerful they can be felt thousands of miles away.

The spot on the surface just above where an earthquake starts is called the epicenter. Ripples called seismic waves travel out from the epicenter. This causes vibrations that people can feel, sometimes very far from the epicenter.

How far away people can feel an earthquake's vibrations depends on its size, or magnitude. Scientists base the magnitude on the strength and duration of the quake's seismic waves. The higher the number, the more powerful the earthquake: A magnitude 3 to 4.9 earthquake is considered minor; 5 to 6.9 is moderate to strong; 7 to 7.9 is major; and 8 or more is an extremely powerful temblor.

As the crust settles after an earthquake, another temblor called an aftershock can happen. Usually, aftershocks are not as powerful as the first quake but can still be very strong.

Geologists can't predict earthquakes. But they're working to change that with new research and technology.

Where earthquakes happen

Earthquakes occur along faults, the areas where tectonic plates meet. About 80 percent of earthquakes occur along the rim of the Pacific Ocean. Called the Ring of Fire because of the large number of volcanoes there, the area is a meeting point for many tectonic plates.

Earthquakes are also common in California because the region sits on top of the Pacific and North American tectonic plates. Temblors happen when these two plates grind against each other. About two-thirds of this movement happens along the San Andreas Fault.

Another major earthquake area in the United States is the New Madrid Seismic Zone, which affects Missouri, Arkansas, Tennessee, Kentucky, and Illinois.

How to survive an earthquake

Earthquakes can happen anytime or anywhere-even if you don't live near a fault. So it's a good idea to prepare.

* Talk with your family about the safest places in your home in case an earthquake hits. This could be under a sturdy table or next to an interior wall (one that is not connected to the outside).

* Look for heavy items that could fall or break during a quake, and move them to safer spots.

* Ask your parents to make sure you have an emergency kit containing things like first-aid supplies, a flashlight, a cell phone charger, and a battery-operated radio. Your family should also have enough food and water for at least 72 hours

DURING AN EARTHQUAKE: Most earthquakes last only 10 to 30 seconds, so it's important to get to a safe place fast. Remember three things during an earthquake: drop, cover, and hold on.

Drop: Get down on your hands and knees and crawl to your shelter.

Cover: Underneath a sturdy table, desk, or bed, cover your head and neck with your arms. If furniture isn't nearby, crouch down on your knees with your arms over your head and neck next to an interior wall. (Don't stand under a doorway-they can easily collapse.)

Hold on: If you're under a piece of furniture, hold on with one hand and move with the furniture if it starts sliding. Stay where you are until the shaking stops.

AFTER AN EARTHQUAKE: Once the earthquake ends, check for injuries. Listen to a radio for any warnings and instructions from official organizations like the United States Geological Survey. Be prepared for any aftershocks.

Text and images adapted from Everything Volcanoes and Earthquakes: Earthshaking photos, facts, and fun!

(Learn more about earthquakes at National Geographic.)

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Learn the science behind how earthquakes happen-and how you can stay safe if one hits.

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Droughts in the United States Facts for Kids

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Droughts in the United States Facts for Kids

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Droughts in the United States is similar to drought around other parts of the world. Below-normal precipitation leads to drought. That's caused by an above average persistence of high pressure over a dry area.

Drought in the United States occurs during climate cycles, such as the North Atlantic oscillation, Atlantic multidecadal oscillation and the El Niño-Southern Oscillation. These determine what areas are more likely to have development of drought and when drought develops.

Droughts are periodic. They alternate with floods over a series of years.

The worst droughts in U.S. history happened in the 1930s and 1950s. The U.S. drought in the 1930s was called the Dust Bowl. The 1936 North American heat wave was part of the Dust Bowl.

Other major droughts in the 20th and 21st centuries happened in the United States in the 1960s, 1980, 1983, 1988-90, 2002 and 2012-14.

The costliest drought in United States history was the 1988-90 drought. The drought caused just over $60 billion in damage. During the drought, there were also heat waves that took the lives of 4,800-17,000 people in the U.S. This drought was also the costliest natural disaster in U.S. history before Hurricane Katrina.

Droughts can affect anywhere within the United States. But the Midwest, Great Plains and Western United States are most likely to be affected by droughts.

Images for kids

La Niña's impact on global climate

Folsom Lake reservoir during the California drought in 2015

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Droughts in the United States Facts for Kids

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Droughts in the United States is similar to drought around other parts of the world. Below-normal precipitation leads to drought. That's caused by an above average persistence of high pressure over a dry area. Drought in the United States occurs during climate cycles, such as the North Atlantic oscillation, Atlantic multidecadal oscillation and the El Niño-Southern Oscillation.

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An earthquake (or quakes, tremors) is shaking of the surface of earth, caused by sudden movement in the Earth's crust. They can be extremely violent.

Earthquakes are usually quite brief, but may repeat. They are the result of a sudden release of energy in the Earth's crust. This creates seismic waves, which are waves of energy that travel through the Earth. The study of earthquakes is called seismology. Seismology studies the frequency, type and size of earthquakes over a period of time.

There are large earthquakes and small earthquakes. Large earthquakes can take down buildings and cause death and injury. Earthquakes are measured using observations from seismometers. The magnitude of an earthquake, and the intensity of shaking, is usually reported on the Richter scale. On the scale, 3 or less is scarcely noticeable, and magnitude 7 (or more) causes damage over a wide area.

An earthquake under the ocean can cause a tsunami. This can cause just as much death and destruction as the earthquake itself. Landslides can happen, too. Earthquakes are part of the Earth's rock cycle.

The ancient Chinese used a device that looked like a jar with dragons on the top surrounded by frogs with their mouths open. When an earthquake occurred, a ball fitted into each dragon's mouth would drop out of the dragon's mouth into the frog's. The position of the frog which received a ball indicated the direction of the earthquake. This was one of the first tools to help figure out where an earthquake originated from.

Causes of an earthquake

Earthquakes are caused by tectonic movements in the Earth's crust. The main cause is that when tectonic plates collide, one rides over the other, causing orogeny (mountain building), earthquakes and volcanoes.

The boundaries between moving plates form the largest fault surfaces on Earth. When they stick, relative motion between the plates leads to increasing stress. This continues until the stress rises and breaks, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy.

Earthquake fault types

There are three main types of geological fault that may cause an earthquake: normal, reverse (thrust) and strike-slip. Normal faults occur mainly in areas where the crust is being extended. Reverse faults occur in areas where the crust is being shortened. Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other.

Earthquake clusters

Most earthquakes form part of a sequence, related to each other in terms of location and time. Most earthquake clusters consist of small tremors which cause little to no damage, but there is a theory that earthquakes can recur in a regular pattern.

A foreshock is an earthquake that occurs before a larger earthquake, called the mainshock. A foreshock is in the same area of the main shock but always of a smaller magnitude.

An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. An aftershock is in the same region of the main shock but always of a smaller magnitude. Aftershocks are formed as the crust adjusts to the effects of the main shock.

Earthquake swarms are sequences of earthquakes striking in a specific area within a short period of time. They are different from earthquakes followed by a series of aftershocks by the fact that no single earthquake in the sequence is obviously the main shock, therefore none have notably higher magnitudes than the other. An example of an earthquake swarm is the 2004 activity at Yellowstone National Park.

Sometimes a series of earthquakes occur in a sort of earthquake storm, where the earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks but on adjacent segments of fault, these storms occur over the course of years, and with some of the later earthquakes as damaging as the early ones. Such a pattern occurred in the North Anatolian fault in Turkey in the 20th century.

Tsunami or a chain of fast moving waves in the ocean caused by powerful earthquakes is a very serious challenge for people's safety and for earthquake engineering. Those waves can inundate coastal areas, destroy houses and even swipe away whole towns.

Unfortunately, tsunamis can not be prevented. However, there are warning systems which may warn the population before the big waves reach the land to let them enough time to rush to safety.

Earthquake-proofing

Some places, such as Japan or California, have many earthquakes and many inhabitants. There, it is good practice to construct houses and other buildings which will resist collapse in an earthquake. This is called seismic design or " earthquake-proofing".

Earthquake-proof buildings are constructed to withstand the destructive force of an earthquake. This depends upon its type of construction, shape, mass distribution, and rigidity. Different combinations are used. Square, rectangular, and shell-shaped buildings can withstand earthquakes better than skyscrapers. To reduce stress, a building's ground floor can be supported by extremely rigid, hollow columns, while the rest of the building is supported by flexible columns inside the hollow columns. Another method is to use rollers or rubber pads to separate the base columns from the ground, allowing the columns to shake parallel to each other during an earthquake.

To help prevent a roof from collapsing, builders make the roof out of light-weight materials. Outdoor walls are made with stronger and more reinforced materials such as steel or reinforced concrete. During an earthquake flexible windows may help hold the windows together so they don't break.

Related pages

Images for kids

Earthquake epicenters occur mostly along tectonic plate boundaries, and especially on the Pacific Ring of Fire.

Comparison of the 1985 and 2017 earthquakes on Mexico City, Puebla and Michoacán/Guerrero

Ruins of the Għajn Ħadid Tower, which collapsed during the 1856 Heraklion earthquake

An image from a 1557 book depicting an earthquake in Italy in the 4th century BCE

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An earthquake (or quakes, tremors) is shaking of the surface of earth, caused by sudden movement in the Earth's crust. They can be extremely violent. Earthquakes are usually quite brief, but may repeat. They are the result of a sudden release of energy in the Earth's crust.

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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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A tropical cyclone is a circular air movement that starts over the warm ocean waters in the warm part of Earth near the Equator. Most tropical cyclones create fast winds and great rains. While some tropical cyclones stay out in the sea, others pass over land. They can be dangerous because of flooding and because the winds pick up objects, including things as big as small boats. Tropical cyclones can throw these things at high speeds.

Tropical cyclones, hurricanes or typhoons form when convection causes warm, moist air above the ocean to rise. They begin as a group of storms when the water gets as hot as 80 °F (27 °C) or hotter. The Coriolis effect made by the Earth's rotation causes the winds to rotate. Warm air rises quickly. Tropical cyclones usually move westward in the tropics, and can later move north or south into the temperate zone. The " eye of the storm" is the center. It has little rain or wind. The eye wall has the heaviest rain and the fastest winds. It is surrounded by rain bands which also have fast winds.

Tropical cyclones are powered by warm, humid ocean air. When they go onto land, they weaken. They die when they spend a long time over land or cool ocean water.

Tropical cyclones are usually given names because it helps in forecasting, locating, and reporting. They are named once they have steady winds of 62 km/h. Committees of the World Meteorological Organization pick names. Once named, a cyclone is usually not renamed.

For several hundred years hurricanes were named after saints. In 1887, Australian meteorologist Clement Wragge began giving women's names to tropical cyclones. He thought of history and mythology for names. When he used men's names, they were usually of politicians he hated. By World War II cyclone names were based on the phonetic alphabet (Able, Baker, Charlie). In 1953 the United States stopped using phonetic names and began using female names for these storms. This ended in 1978 when both male and female names were used for Pacific storms. In 1979 this practice was added for hurricanes in the Gulf of Mexico and the Atlantic.

Classifications

Tropical cyclones are classified into different categories by their strength and location. The National Hurricane Center, which observes hurricanes in the Atlantic Ocean and Eastern and Central Pacific Ocean, classifies them using the Saffir-Simpson Hurricane Scale.

Tropical cyclones in other places such as the Western Pacific Ocean or the Southern Hemisphere are classified on scales that are quite a bit like the Saffir-Simpson Scale. For example; if a tropical storm in the western Pacific reaches hurricane-strength winds, it is then officially called a typhoon.

A tropical depression is an organized group of clouds and thunderstorms with a clear circulation in air near the ocean and maximum continuing winds of less than 17 m/s (33 kt, 38 mph, or 62 km/h). It has no eye and does not usually have the spiral shape that more powerful storms have. Only the Philippines are known to name tropical depressions.

A tropical storm is an organized system of strong thunderstorms with a very clear surface circulation and continuing winds between 17 and 32 m/s (34-63 kt, 39-73 mph, or 62-117 km/h). At this point, the cyclonic shape starts to form, although an eye does not usually appear in tropical storms. Most tropical cyclone agencies start naming cyclonic storms at this level, except for the Philippines which have their own way of naming cyclones.

A hurricane or typhoon or a cyclone is a large cyclonic weather system with continuing winds of at least 33 m/s (64 kt, 74 mph, or 118 km/h). A tropical cyclone with this wind speed usually develops an eye, which is an area of calm conditions at the center of its circulation. The eye is often seen from space as a small, round, cloud-free spot. Around the eye is the eye wall, an area where the strongest thunderstorms and winds spin around the storm's center. The fastest possible continuing wind speed found in tropical cyclones is thought to be around 85 m/s (165 kt, 190 mph, 305 km/h).

Tropical cyclone, typhoon or hurricane

The term "tropical cyclone" is a summary term. In various places tropical cyclones have other local names such as "hurricane" and "typhoon". A tropical cyclone that forms in the Atlantic Ocean is called a hurricane. The word hurricane is also used for those that form in the eastern, central and northern Pacific. In the western Pacific a tropical cyclone is called a typhoon. In the Indian Ocean it is called a "cyclone".

Tropical cyclones tend to develop during the summer, but have been noted in nearly every month in most tropical cyclone basins. Tropical cyclones on either side of the Equator generally have their origins in the Intertropical Convergence Zone, where winds blow from either the northeast or southeast. Within this broad area of low-pressure, air is heated over the warm tropical ocean and rises in discrete parcels, which causes thundery showers to form. These showers dissipate quite quickly; however, they can group together into large clusters of thunderstorms. This creates a flow of warm, moist, rapidly rising air, which starts to rotate cyclonically as it interacts with the rotation of the earth.

Several factors are required for these thunderstorms to develop further, including sea surface temperatures of around 27 °C (81 °F) and low vertical wind shear surrounding the system, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low-pressure center, and a pre-existing low-level focus or disturbance.

Rapid intensification

On occasion, tropical cyclones may undergo a process known as rapid intensification, a period in which the maximum sustained winds of a tropical cyclone increase by 30 kn (56 km/h; 35 mph) or more within 24 hours. Similarly, rapid deepening in tropical cyclones is defined as a minimum sea surface pressure decrease of 1.75 hPa (0.052 inHg) per hour or 42 hPa (1.2 inHg) within a 24-hour period; explosive deepening occurs when the surface pressure decreases by 2.5 hPa (0.074 inHg) per hour for at least 12 hours or 5 hPa (0.15 inHg) per hour for at least 6 hours. For rapid intensification to occur, several conditions must be in place. Water temperatures must be extremely high (near or above 30 °C (86 °F)), and water of this temperature must be sufficiently deep such that waves do not upwell cooler waters to the surface.

Dissipation

There are a number of ways a tropical cyclone can weaken, dissipate, or lose its tropical characteristics. These include making landfall, moving over cooler water, encountering dry air, or interacting with other weather systems; however, once a system has dissipated or lost its tropical characteristics, its remnants could regenerate a tropical cyclone if environmental conditions become favorable.

A tropical cyclone can dissipate when it moves over waters significantly cooler than 26.5 °C (79.7 °F). This will deprive the storm of such tropical characteristics as a warm core with thunderstorms near the center, so that it becomes a remnant low-pressure area. Remnant systems may persist for several days before losing their identity. This dissipation mechanism is most common in the eastern North Pacific.

Should a tropical cyclone make landfall or pass over an island, its circulation could start to break down, especially if it encounters mountainous terrain. When a system makes landfall on a large landmass, it is cut off from its supply of warm moist maritime air and starts to draw in dry continental air. This, combined with the increased friction over land areas, leads to the weakening and dissipation of the tropical cyclone. Over a mountainous terrain, a system can quickly weaken; however, over flat areas, it may endure for two to three days before circulation breaks down and dissipates.

Over the years, there have been a number of techniques considered to try to artificially modify tropical cyclones. These techniques have included using nuclear weapons, cooling the ocean with icebergs, blowing the storm away from land with giant fans, and seeding selected storms with dry ice or silver iodide. These techniques, however, fail to appreciate the duration, intensity, power or size of tropical cyclones.

In the past these storms sank many ships. Better weather forecasting in the 20th century helped most ships avoid them. When tropical cyclones reach land, they may break things. Sometimes they kill people and destroy cities. In the last 200 years, about 1.5 million people have been killed by tropical cyclones.

Wind can cause up to 83% of the total damages of a storm. Broken wreckage from destroyed objects can become deadly flying pieces. Flooding can also occur when a lot of rain falls and/or when storm surges push water onto the land.

There is a possibility of "indirect" deaths after a tropical cyclone passes. For example, New Orleans, Louisiana suffered from poor health conditions after Hurricane Katrina hit in 2005.

Related pages

Images for kids

Hurricane Gustav on September 9, 2002, the first system to be given a name as a subtropical cyclone

In Spanish: Ciclón tropical para niños

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Tornado Facts For Kids

Enjoy our fun tornado facts for kids! Learn what tornadoes are, how fast they spin, how far they can travel, where most tornadoes occur, the difference between an F0 tornado and an F5 tornado, what a waterspout is and much more.

Read on to check out our wide range of information on twisters.

A tornado is a rapidly spinning tube of air that touches both the ground and a cloud above.

Tornadoes are sometimes called twisters.

Not all tornadoes are visible but their high wind speeds and rapid rotation often form a visible funnel of condensed water.

The Fujita Scale is a common way of measuring the strength of tornadoes. The scale ranges from F0 tornadoes that cause minimal damage through to F5 tornadoes which cause massive damage.

Most tornadoes have wind speeds less than 100 miles per hour (161 kilometres per hour).

Extreme tornadoes can reach wind speeds of over 300 miles per hour (483 kilometres per hour).

Most tornadoes travel a few miles before exhausting themselves.

Extreme tornadoes can travel much further, sometimes over 100 miles (161kilometres).

The Tri-State Tornado that travelled through parts of Missouri, Illinois and Indiana in 1925 left a path of destruction over 219 miles (352 kilometres) long.

The Tri-State Tornado was the deadliest tornado in US history, killing 695 people.

The USA averages around 1200 tornadoes every year, more than any other country.

The majority of these tornadoes occur in a geographically unique area nicknamed 'Tornado Alley'.

US States most often hit by tornadoes include Texas, Kansas, Oklahoma and Florida.

In 1989 the deadliest tornado ever recorded in the world killed around 1300 people in Bangladesh.

In the southern hemisphere tornadoes usually rotate in a clockwise direction.

In the northern hemisphere tornadoes usually rotate in a counterclockwise direction.

A tornado that occurs over water is often called a waterspout.

Weather radars are used to detect tornadoes and give advanced warning.

Basements and other underground areas are the safest places to seek refuge during a tornado. It is also a good idea to stay away from windows.

Make a tornado in a bottle or watch some amazing tornado video footage.

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Fun Tornado Facts for Kids - Interesting Information about Twisters

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Tornado Facts For Kids Enjoy our fun tornado facts for kids! Learn what tornadoes are, how fast they spin, how far they can travel, where most tornadoes occur, the difference between an F0 tornado and an F5 tornado, what a waterspout is and much more.

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Enjoy our awesome range of Earth facts for kids. Check out the cool trivia and have fun learning about some of our planet's most amazing features.

Earthquake Facts

Check out our interesting earthquake facts for kids. Find a range of information that will teach you what causes earthquakes as well as some examples of notable earthquakes that have shaken countries around the world in recent times.

Earthquakes involve the powerful movement of rocks in the Earth's crust. The rapid release of energy creates seismic waves that travel through the earth.

Scientists use the different speeds of seismic waves to locate the epicentre (the point on the surface directly above where the earthquake originated) of earthquakes.

Seismometers are used to measure the magnitude of earthquakes. You are unlikely to feel a magnitude 3 earthquake but a magnitude 6 earthquake could potentially cause large damage.

The damage caused by earthquakes also depends on their depth and fault type.

The earthquake that hit the Tohoku region of Japan on March 11, 2011, had a magnitude of 9.0 and killed over 15000 people.

The destruction caused by the Tohoku earthquake was made much worse by powerful tsunamis that were triggered due to the earthquake's epicentre being located offshore. More tsunami facts.

The 2004 earthquake that occurred in the Indian Ocean near Sumatra, Indonesia triggered a series of tsunamis that killed over 200000 people in 14 countries.

The February 2011 earthquake in Christchurch, New Zealand followed nearly 6 months after a magnitude 7.1 earthquake shook the region. The earthquake killed 181 people and significantly damaged the central city. The economic damage caused by the earthquake and aftershocks is estimated to be around $15 billion (NZ$).

An earthquake that hit Haiti in January 2010 with a magnitude of 7.0 killed over 200000 people according to Haitian sources.

The most powerful earthquake ever recorded on Earth was in Valdivia, Chile. Occurring in 1960, it had a magnitude of 9.5.

It is important in earthquake prone countries such as Japan to build houses and buildings that react well to earthquakes. Good engineering practises can help stop buildings collapsing under the stress of large earthquakes.

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Earthquake Facts for Kids - Interesting Information about Earthquakes

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Enjoy our awesome range of Earth facts for kids. Check out the cool trivia and have fun learning about some of our planet's most amazing features. Earthquake Facts Check out our interesting earthquake facts for kids.

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Enjoy our awesome range of Earth facts for kids. Check out the cool trivia and have fun learning about some of our planet's most amazing features.

Fun Volcano Facts

Check out these fun volcano facts for kids. Learn about hot magma, famous eruptions, volcanoes on other planets, volcanic gases, flowing lava and more. Enjoy our wide range of strange and interesting facts about volcanoes.

Volcanoes are openings in the Earth's surface. When they are active they can let ash, gas and hot magma escape in sometimes violent and spectacular eruptions.

The word volcano originally comes from the name of the Roman god of fire, Vulcan.

Volcanoes are usually located where tectonic plates meet. This is especially true for the Pacific Ring of Fire, an area around the Pacific Ocean where over 75% of the volcanoes on Earth are found.

While most volcanoes form near tectonic boundaries, they can also form in areas that contain abnormally hot rock inside the Earth. Known as mantle plumes, these hotspots are found at a number of locations around the globe with the most notable being in Hawaii.

Hot liquid rock under the Earth's surface is known as magma, it is called lava after it comes out of a volcano.

Some famous volcanic eruptions of modern times include Mount Krakatoa in 1883, Novarupta in 1912, Mount St Helens in 1980 and Mt Pinatubo in 1991.

While we certainly have some big volcanoes here on Earth, the biggest known volcano in our solar system is actually on Mars. Its name is Olympus Mons and it measures a whooping 600km (373 miles) wide and 21km (13 miles) high.

The object with the most volcanic activity in our solar system is Io, one of Jupiter's moons. Covered in volcanoes, its surface is constantly changing to the large amount of volcanic activity.

Most people think of volcanoes as large cone shaped mountains but that is just one type, others feature wide plateaus, fissure vents (cracks were lava emerges) and bulging dome shapes.

There are also volcanoes found on the ocean floor and even under icecaps, such as those found in Iceland.

Volcanoes can be active (regular activity), dormant (recent historical activity but now quiet) or extinct (no activity in historical times and unlikely to erupt again). While these terms are useful, scientists are more likely to describe volcanoes by characteristics such a how they formed, how they erupt and what their shape is.

Common volcanic gases include water vapor, carbon dioxide, sulfur dioxide, hydrogen chloride, hydrogen fluoride and hydrogen sulfide.

Volcanic eruptions can send ash high into the air, over 30km (17 miles) above the Earth's surface.

Scientists monitor volcanic activity with satellite imagery and sensors on the ground, helping predict when eruptions might occur.

Large volcanic eruptions can reflect radiation from the Sun and drop average temperatures on Earth by around half a degree. There have been several examples of this over the last century.

Pumice is a unique volcanic rock ( igneous) that can float in water. It can also be used as an abrasive and is sometimes used in beauty salons for removing dry skin.

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Fun Volcano Facts for Kids - Interesting Facts about Volcanoes

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Enjoy our awesome range of Earth facts for kids. Check out the cool trivia and have fun learning about some of our planet's most amazing features. Fun Volcano Facts Check out these fun volcano facts for kids. Learn about hot magma, famous eruptions, volcanoes on other planets, volcanic gases, flowing lava and more.

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Read National Geographic Kids Everything Volcanoes and Earthquakes on Epic

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Read National Geographic Kids Everything Volcanoes and Earthquakes on Epic

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Enjoy our awesome range of Earth facts for kids. Check out the cool trivia and have fun learning about some of our planet's most amazing features.

Tsunami Facts

Check out our tsunami facts for kids and learn some interesting information related to these great walls of water that can cause so much destruction. Find out what causes tsunamis and read about some notable recent examples of tsunamis that have occurred around the globe.

Tsunamis are huge waves of water that are usually caused by earthquakes or volcanic eruptions.

As a tsunami approaches the shore, water may recede from the coast, if it is shallow enough the water may be pulled back hundreds of metres. If you are in the area, observing this is a good indication that a tsunami is on the way.

Regions in tsunami danger zones often have warning systems in place to give people as much time to evacuate as possible.

When tsunamis hit shallow water (often near the coast) they slow down but increase in height.

An earthquake in the Indian Ocean off Indonesia in December 2004 caused a tsunami that killed over 200000 people in 14 countries. More earthquake facts.

In March 2011, the Tohoku earthquake off the eastern coast of Japan caused a tsunami that was a major factor in the death of over 15000 people.

The tsunami waves created by the Tohoku earthquake reached heights of over 40 metres (131 feet) in some areas, wiping out coastal towns and causing a number of nuclear accidents.

The Japanese word tsunami literally means 'harbor wave'.

Tsunamis are sometimes referred to as tidal waves but this term has fallen out of favour because tsunamis are not related to tides.

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Tsunami Facts for Kids - Interesting Information about Tsunamis

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Enjoy our awesome range of Earth facts for kids. Check out the cool trivia and have fun learning about some of our planet's most amazing features. Tsunami Facts Check out our tsunami facts for kids and learn some interesting information related to these great walls of water that can cause so much destruction.

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Welcome to Hawai'i Volcanoes National Park

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Welcome to Hawai'i Volcanoes National Park

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How Volcanoes Form

In 1980 in Washington, after 123 years of hibernation, Mount St. Helens erupted. The blast destroyed and scorched 230 square miles (370 square kilometers) of forest within minutes. The eruption released an avalanche of hot ash, gas, steam, and rocks that mowed down giant trees up to 15 miles (24 kilometers) away.

When magma finds a way to escape from beneath the earth's surface, it creates a volcano.

Volcanoes erupt in different ways. Some, like Mount St. Helens, explode. Explosive eruptions are so powerful, they can shoot particles 20 miles up (32 kilometers), hurl 8-ton boulders more than a half mile (0.8 kilometers) away, and cause massive landslides. Explosive eruptions also create an avalanche of hot volcanic debris, ash, and gas that bulldozes everything in its path. Explosive volcanoes cause most of the volcano-related fatalities.

Volcanoes, like Mauna Loa in Hawaii, are effusive. Rather than a violent explosion, lava pours or flows out. Fatalities from effusive volcanoes are rare because people can usually outrun the lava. However, some people get too close or become trapped with no escape. The flowing lava burns, melts, and destroys everything it touches including farms, houses, and roads.

A volcanic eruption forever changes the landscape. Though volcanoes destroy, they also create mountains, islands, and, eventually, incredibly fertile land.

Carpet of Ash

Volcanic eruptions can cause damage hundreds of miles away. Volcanic ash causes airplane engines to fail, destroys crops, contaminates water, and damages electronics and machinery. The ash carpets the ground, burying everything, sometimes even causing buildings to collapse. Mount St. Helens produced more than 490 tons of ash that fell over a 22,000 square mile (56,980 square kilometer) area and caused problems in cities 370 miles (600 kilometers) away.

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When magma finds a way to escape from beneath the earth's surface, it creates a volcano.

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Advanced warning systems, combined with community education, can reduce tsunami casualties

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Each volcano has unique warning signs that eruption is imminent

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Each volcano has unique warning signs that eruption is imminent

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Newsela | Each volcano has unique warning signs that eruption is imminent

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All About Glaciers for Kids: How Glaciers Form and Erode to Create Landforms - FreeSchool

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BrainPOP - Animated Educational Site for Kids - Science, Social Studies, English, Math, Arts & Music, Health, and Technology

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MUDSLIDE SAFETY

Mudslides occur during periods of intense rainfall or rapid snowmelt. They usually start on steep hillsides, liquefy and accelerate down the hill. The debris flow ranges from watery mud to thick, rocky mud that can carry large items such as boulders, trees and cars. On average, mudslides cause 25 to 50 deaths each year. Always listen to the radio and television for the latest information and instructions for your area.

BEFORE INTENSE STORMS:

Have a disaster plan.

Become familiar with the land around you. Find out if you're in a mudslide prone area.

DURING INTENSE STORMS:

Stay awake and alert.

If you live in mudslide prone areas, consider leaving if it safe to do so. If you can't, go to the highest level of your home.

Listen for unusual sounds that might indicate moving debris, such as trees cracking or boulders knocking each other.

Be alert especially when driving. Watch the road for collapsed pavement, mud, fallen rocks and other indications of a possible debris flow.

DURING A MUDSLIDE:

Quickly move out of the path of the mudslide.

If you can't escape, curl into a tight ball and protect your head.

AFTER A MUDSLIDE:

Stay away from mudslide areas.

Check for injured or trapped people near the mudslide, without directly entering the area.

Watch out for flooding which can happen after a mudslide.

Check the foundation of your home, chimney and surrounding land for damage.

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Weather Wiz Kids weather information for kids

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Weather Wiz Kids is a fun and safe website for kids about all the weather info they need to know. It contains tools for weather education, including weather games, activities, experiments, photos, a glossary and educational teaching materials for the classroom.

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Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, characterized by either steep or gentle slope gradients, from mountain ranges to coastal cliffs or even underwater, in which case they are called submarine landslides. Gravity is the primary driving force for a landslide to occur, but there are other factors affecting slope stability that produce specific conditions that make a slope prone to failure. In many cases, the landslide is triggered by a specific event (such as a heavy rainfall, an earthquake, a slope cut to build a road, and many others), although this is not always identifiable.

Landslides occur when the slope (or a portion of it) undergoes some processes that change its condition from stable to unstable. This is essentially due to a decrease in the shear strength of the slope material, an increase in the shear stress borne by the material, or a combination of the two. A change in the stability of a slope can be caused by a number of factors, acting together or alone. Natural causes of landslides include:

saturation by rain water infiltration, snow melting, or glaciers melting;

rising of groundwater or increase of pore water pressure (e.g. due to aquifer recharge in rainy seasons, or by rain water infiltration);

increase of hydrostatic pressure in cracks and fractures;

loss or absence of vertical vegetative structure, soil nutrients, and soil structure (e.g. after a wildfire - a fire in forests lasting for 3-4 days);

erosion of the top of a slope by rivers or sea waves;

physical and chemical weathering (e.g. by repeated freezing and thawing, heating and cooling, salt leaking in the groundwater or mineral dissolution);

ground shaking caused by earthquakes, which can destabilize the slope directly (e.g., by inducing soil liquefaction) or weaken the material and cause cracks that will eventually produce a landslide;

volcanic eruptions;

Landslides are aggravated by human activities, such as:

temporal variation in land use and land cover (LULC): it includes the human abandonment of farming areas, e.g. due to the economic and social transformations which occurred in Europe after the Second World War. Land degradation and extreme rainfall can increase the frequency of erosion and landslide phenomena.

Hungr-Leroueil-Picarelli classification

In traditional usage, the term landslide has at one time or another been used to cover almost all forms of mass movement of rocks and regolith at the Earth's surface. In 1978, geologist David Varnes noted this imprecise usage and proposed a new, much tighter scheme for the classification of mass movements and subsidence processes. This scheme was later modified by Cruden and Varnes in 1996, and refined by Hutchinson (1988), Hungr et al. (2001), and finally by Hungr, Leroueil and Picarelli (2014). The classification resulting from the latest update is provided below.

Under this classification, six types of movement are recognized. Each type can be seen both in rock and in soil. A fall is a movement of isolated blocks or chunks of soil in free-fall. The term topple refers to blocks coming away by rotation from a vertical face. A slide is the movement of a body of material that generally remains intact while moving over one or several inclined surfaces or thin layers of material (also called shear zones) in which large deformations are concentrated. Slides are also sub-classified by the form of the surface(s) or shear zone(s) on which movement happens. The planes may be broadly parallel to the surface ("planar slides") or spoon-shaped ("rotational slides"). Slides can occur catastrophically, but movement on the surface can also be gradual and progressive. Spreads are a form of subsidence, in which a layer of material cracks, opens up, and expands laterally. Flows are the movement of fluidised material, which can be both dry or rich in water (such as in mud flows). Flows can move imperceptibly for years, or accelerate rapidly and cause disasters. Slope deformations are slow, distributed movements that can affect entire mountain slopes or portions of it. Some landslides are complex in the sense that they feature different movement types in different portions of the moving body, or they evolve from one movement type to another over time. For example, a landslide can initiate as a rock fall or topple and then, as the blocks disintegrate upon the impact, transform into a debris slide or flow. An avalanching effect can also be present, in which the moving mass entrains additional material along its path.

Slope material that becomes saturated with water may produce a debris flow or mud flow. However, also dry debris can exhibit flow-like movement. Flowing debris or mud may pick up trees, houses and cars, and block bridges and rivers causing flooding along its path. This phenomenon is particularly hazardous in alpine areas, where narrow gorges and steep valleys are conducive of faster flows. Debris and mud flows may initiate on the slopes or result from the fluidization of landslide material as it gains speed or incorporates further debris and water along its path. River blockages as the flow reaches a main stream can generate temporary dams. As the impoundments fail, a domino effect may be created, with a remarkable growth in the volume of the flowing mass, and in its destructive power.

An earthflow is the downslope movement of mostly fine-grained material. Earthflows can move at speeds within a very wide range, from as low as 1 mm/yr to many km/h. Though these are a lot like mudflows, overall they are more slow-moving and are covered with solid material carried along by the flow from within. Clay, fine sand and silt, and fine-grained, pyroclastic material are all susceptible to earthflows. These flows are usually controlled by the pore water pressures within the mass, which should be high enough to produce a low shearing resistance. On the slopes, some earthflow may be recognized by their elongated shape, with one or more lobes at their toes. As these lobes spread out, drainage of the mass increases and the margins dry out, lowering the overall velocity of the flow. This process also causes the flow to thicken. Earthflows occur more often during periods of high precipitation, which saturates the ground and builds up water pressures. However, earthflows that keep advancing also during dry seasons are not uncommon. Fissures may develop during the movement of clayey materials, which facilitate the intrusion of water into the moving mass and produce faster responses to precipitation.

A rock avalanche, sometimes referred to as sturzstrom, is a large and fast-moving landslide of the flow type. It is rarer than other types of landslides but it is often very destructive. It exhibits typically a long runout, flowing very far over a low-angle, flat, or even slightly uphill terrain. The mechanisms favoring the long runout can be different, but they typically result in the weakening of the sliding mass as the speed increases. The causes of this weakening are not completely understood. Especially for the largest landslides, it may involve the very quick heating of the shear zone due to friction, which may even cause the water that is present to vaporize and build up a large pressure, producing a sort of hovercraft effect. In some cases, the very high temperature may even cause some of the minerals to melt. During the movement, the rock in the shear zone may also be finely ground, producing a nanometer-size mineral powder that may act as a lubricant, reducing the resistance to motion and promoting larger speeds and longer runouts. The weakening mechanisms in large rock avalanches are similar to those occurring in seismic faults.

Slides can occur in any rock or soil material and are characterized by the movement of a mass over a planar or curvilinear surface or shear zone.

A debris slide is a type of slide characterized by the chaotic movement of material mixed with water and/or ice. It is usually triggered by the saturation of thickly vegetated slopes which results in an incoherent mixture of broken timber, smaller vegetation and other debris. Debris flows and avalanches differ from debris slides because their movement is fluid-like and generally much more rapid. This is usually a result of lower shear resistances and steeper slopes. Debris slides generally begin with the detachment of rock chunks high on the slopes, which break apart as they slide towards the bottom.

Clay and silt slides are usually slow but can experience episodic acceleration in response to heavy rainfall or rapid snowmelt. They are often seen on gentle slopes and move over planar surfaces, such as over the underlying bedrock. Failure surfaces can also form within the clay or silt layer itself, and they usually have concave shapes, resulting in rotational slides

Shallow and deep-seated landslides

A landslide in which the sliding surface is located within the soil mantle or weathered bedrock (typically to a depth from few decimeters to some meters) is called a shallow landslide. Debris slides and debris flows are usually shallow. Shallow landslides can often happen in areas that have slopes with high permeable soils on top of low permeable soils. The low permeable soil traps the water in the shallower soil generating high water pressures. As the top soil is filled with water, it can become unstable and slide downslope.

Deep-seated landslides are those in which the sliding surface is mostly deeply located, for instance well below the maximum rooting depth of trees. They usually involve deep regolith, weathered rock, and/or bedrock and include large slope failures associated with translational, rotational, or complex movements. They tend to form along a plane of weakness such as a fault or bedding plane. They can be visually identified by concave scarps at the top and steep areas at the toe.

Causing tsunamis

Landslides that occur undersea, or have impact into water e.g. significant rockfall or volcanic collapse into the sea, can generate tsunamis. Massive landslides can also generate megatsunamis, which are usually hundreds of meters high. In 1958, one such tsunami occurred in Lituya Bay in Alaska.

Related phenomena

An avalanche, similar in mechanism to a landslide, involves a large amount of ice, snow and rock falling quickly down the side of a mountain.

A pyroclastic flow is caused by a collapsing cloud of hot ash, gas and rocks from a volcanic explosion that moves rapidly down an erupting volcano.

Landslide prediction mapping

Landslide hazard analysis and mapping can provide useful information for catastrophic loss reduction, and assist in the development of guidelines for sustainable land-use planning. The analysis is used to identify the factors that are related to landslides, estimate the relative contribution of factors causing slope failures, establish a relation between the factors and landslides, and to predict the landslide hazard in the future based on such a relationship. The factors that have been used for landslide hazard analysis can usually be grouped into geomorphology, geology, land use/land cover, and hydrogeology. Since many factors are considered for landslide hazard mapping, GIS is an appropriate tool because it has functions of collection, storage, manipulation, display, and analysis of large amounts of spatially referenced data which can be handled fast and effectively. Cardenas reported evidence on the exhaustive use of GIS in conjunction of uncertainty modelling tools for landslide mapping. Remote sensing techniques are also highly employed for landslide hazard assessment and analysis. Before and after aerial photographs and satellite imagery are used to gather landslide characteristics, like distribution and classification, and factors like slope, lithology, and land use/land cover to be used to help predict future events. Before and after imagery also helps to reveal how the landscape changed after an event, what may have triggered the landslide, and shows the process of regeneration and recovery.

Using satellite imagery in combination with GIS and on-the-ground studies, it is possible to generate maps of likely occurrences of future landslides. Such maps should show the locations of previous events as well as clearly indicate the probable locations of future events. In general, to predict landslides, one must assume that their occurrence is determined by certain geologic factors, and that future landslides will occur under the same conditions as past events. Therefore, it is necessary to establish a relationship between the geomorphologic conditions in which the past events took place and the expected future conditions.

Natural disasters are a dramatic example of people living in conflict with the environment. Early predictions and warnings are essential for the reduction of property damage and loss of life. Because landslides occur frequently and can represent some of the most destructive forces on earth, it is imperative to have a good understanding as to what causes them and how people can either help prevent them from occurring or simply avoid them when they do occur. Sustainable land management and development is also an essential key to reducing the negative impacts felt by landslides.

GIS offers a superior method for landslide analysis because it allows one to capture, store, manipulate, analyze, and display large amounts of data quickly and effectively. Because so many variables are involved, it is important to be able to overlay the many layers of data to develop a full and accurate portrayal of what is taking place on the Earth's surface. Researchers need to know which variables are the most important factors that trigger landslides in any given location. Using GIS, extremely detailed maps can be generated to show past events and likely future events which have the potential to save lives, property, and money.

Since the '90s, GIS have been also successfully used in conjunction to decision support systems, to show on a map real-time risk evaluations based on monitoring data gathered in the area of the Val Pola disaster (Italy).

Trackside rock slide detector on the UPRR Sierra grade near Colfax, CA

Prehistoric landslides

Storegga Slide, some 8,000 years ago off the western coast of Norway. Caused massive tsunamis in Doggerland and other countries connected to the North Sea. A total volume of 3,500 km³ (840 cu mi) debris was involved; comparable to a 34 m (112 ft) thick area the size of Iceland. The landslide is thought to be among the largest in history.

Landslide which moved Heart Mountain to its current location, the largest continental landslide discovered so far. In the 48 million years since the slide occurred, erosion has removed most of the portion of the slide.

Flims Rockslide, ca. 12 km³ (2.9 cu mi), Switzerland, some 10000 years ago in post-glacial Pleistocene/Holocene, the largest so far described in the alps and on dry land that can be easily identified in a modestly eroded state.

The landslide around 200 BC which formed Lake Waikaremoana on the North Island of New Zealand, where a large block of the Ngamoko Range slid and dammed a gorge of Waikaretaheke River, forming a natural reservoir up to 256 metres (840 ft) deep.

Cheekye Fan, British Columbia, Canada, ca. 25 km² (9.7 sq mi), Late Pleistocene in age.

The Manang-Braga rock avalanche/debris flow may have formed Marsyangdi Valley in the Annapurna Region, Nepal, during an interstadial period belonging to the last glacial period. Over 15 km³ of material are estimated to have been moved in the single event, making it one of the largest continental landslides.

A massive slope failure 60 km north of Kathmandu Nepal, involving an estimated 10-15 km³. Prior to this landslide the mountain may have been the world's 15th mountain above 8000m.

Historical landslides

Main page: List of landslides

The 1806 Goldau landslide on September 2, 1806

The Cap Diamant Québec rockslide on September 19, 1889

Frank Slide, Turtle Mountain, Alberta, Canada, on 29 April 1903

Khait landslide, Khait, Tajikistan, Soviet Union, on July 10, 1949

A Magnitude 7.5 earthquake in Yellowstone Park (August 17, 1959) caused a landslide that blocked the Madison River, and created Quake Lake.

Monte Toc landslide (260 million cubic metres, 9.2 billion cubic feet) falling into the Vajont Dam basin in Italy, causing a megatsunami and about 2000 deaths, on October 9, 1963

Hope Slide landslide (46 million cubic metres, 1.6 billion cubic feet) near Hope, British Columbia on January 9, 1965.

The 1966 Aberfan disaster

Tuve landslide in Gothenburg, Sweden on November 30, 1977.

The 1979 Abbotsford landslip, Dunedin, New Zealand on August 8, 1979.

The eruption of Mount St. Helens (May 18, 1980) caused an enormous landslide when the top 1300 feet of the volcano suddenly gave way.

Val Pola landslide during Valtellina disaster (1987) Italy

Thredbo landslide, Australia on 30 July 1997, destroyed hostel.

Vargas mudslides, due to heavy rains in Vargas State, Venezuela, in December, 1999, causing tens of thousands of deaths.

2005 La Conchita landslide in Ventura, California causing 10 deaths.

2007 Chittagong mudslide, in Chittagong, Bangladesh, on June 11, 2007.

2008 Cairo landslide on September 6, 2008.

disaster caused 37 deaths, on October 1.

The 2010 Uganda landslide caused over 100 deaths following heavy rain in Bududa region.

Zhouqu county mudslide in Gansu, China on August 8, 2010.

Devil's Slide, an ongoing landslide in San Mateo County, California

2011 Rio de Janeiro landslide in Rio de Janeiro, Brazil on January 11, 2011, causing 610 deaths.

2014 Pune landslide, in Pune, India.

2014 Oso mudslide, in Oso, Washington

2017 Mocoa landslide, in Mocoa, Colombia

Extraterrestrial landslides

Evidence of past landslides has been detected on many bodies in the solar system, but since most observations are made by probes that only observe for a limited time and most bodies in the solar system appear to be geologically inactive not many landslides are known to have happened in recent times. Both Venus and Mars have been subject to long-term mapping by orbiting satellites, and examples of landslides have been observed on both planets.

In Spanish: Corrimiento de tierra para niños

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A mudflow or mudslide occurs when mud travels down a slope very quickly. Mudflows, which are like giant moving mud pies, happen when lots of water mixes with soil and rock. The water makes the slippery mass of mud flow quickly down. Mudflows happen most in mountainous places where a long dry season is followed by heavy rains.

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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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How Glaciers Change the World! | Winter Science | SciShow Kids

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What are sinkholes?
Sinkholes are pits in the ground that form in areas where water gathers without external drainage. Sinkholes mainly occur as water drains below ground. It can dissolve subterranean caverns, particularly in areas where the bedrock is made of water-soluble evaporate rocks such as salt or gypsum or of carbonate rocks such as limestone or dolomite.

What causes sinkholes?
Sinkholes can be natural or man made. Natural sinkholes occur due to erosion or underground water. They start developing long time before it actually appears. The ground beneath our feet is not as much of a solid structure as we think it is. The ground is made from dirt, along with many rocks and minerals. There is water continually seeping in between the mud, rocks and minerals, as it makes its way down to the ground water reservoirs. As this happens, the water slowly erodes the rocks and minerals. Sometimes the flow of water increases to a point when it washes away the underground structure of the land. And when the structure becomes too weak to support the surface of the earth, it collapses and opens up a hole. This is how sinkholes are formed.

What type of bedrock is more susceptible to sinkholes?
Areas that have a bedrock made of limestone, salt deposits or carbonate rock are most susceptible to erosion and the formation of such holes. These rocks tend to erode as acidic water passes through them. When rainwater passes through decaying plant debris, it tend to become more acidic. Over a period of years, overlying sediments collapse and a sinkhole develops. Sometimes the holes are small, measuring a few feet wide and ten to fifteen feet deep. Others can be hundreds of miles wide and deep. However, all of them can be dangerous for those that get caught in them. There are three major kinds of sinkholes. Their formation is determined by the same geological processes, barring a few differences.

Can humans cause sinkholes?
Yes! Humans are also responsible for the formation of sinkholes. Activities like drilling, mining, construction, broken water or drain pipes, improperly compacted soil after excavation work or even heavy traffic can result in small to large sinkholes. Water from broken pipe can penetrate through mud and rocks and erode the ground underneath and cause sinkholes. Sometimes, heavy weight on soft soil can result in collapse of ground, resulting in a sinkhole. Sinkholes can also form when the land surface is changed.

How quickly do sinkholes form?
Most of the time, sinkholes form gradually. Occasionally, though, the collapse is sudden. Those sudden sinkholes are often the ones that open up and swallow cars, homes and streets.

Why are there so many sinkholes?
Most of the sinkholes we are seeing at the moment are at least indirectly created by human activity. They're occuring just to the sides of human constructions where rain water has been concentrated on a particular patch of ground in the form of run-off from roofs and tarmac. However, these local factors wouldn't matter if it wasn't for the wider picture. The Southeast, where most of the sinkholes have appeared, has not only suffered one of the wettest winters in recent decades, but is also natural sinkhole country as most of the bedrock is the soluble chalk.

What are some notable sinkholes?
In 2010 one of the most devastating sinkholes in recent times hit Guatemala City. An area approximately 65ft wide and 100ft deep collapsed, swallowing a three-story factory and killing 15 people. The sinkhole was caused by a number of factors including an influx of water from Tropical Storm Agatha and leakage from a local sewerage pipe.

On February 12, 2014, a sinkhole some 40ft wide and 20ft deep opened under the floor of the Skydome area of the National Corvette Museum causing a portion of the floor to collapse. Eight rare and one-of-a-kind Corvettes, portions of the display stands and rails, large concrete floor slabs and dirt fell into the sinkhole, causing serious damage to some of the Corvettes. The Corvettes involved have an estimated value of a million dollars.

Do sinkholes happen in other parts of the world?
Yes! The deepest we know about is the Xiaozhai tiankeng in China. Tiankeng is the local term for large sinkholes and translates literally as 'heavenly pit'. This particular example in the Chongqing district is a staggering 662m deep and 626m wide.

Other notable sinkholes include Sima Humboldt in Bolivia, a crater 314m deep and formed from extremely resistant sandstone.

The Great Blue Hole in Belize, a perfectly round hole in the middle of an atoll which is 124m deep.

Finally, Crveno Jezero in Croatia, a 530m deep sinkhole with nearly vertical walls.

How many types of sinkholes are there?
The three major types of sinkholes know to us are : Solution, Cover Collapse and Cover Subsidence.

Solution sinkholes are most commonly seen in areas that have a very thin cover of soil on the surface, exposing the bedrock below to continual erosion by water. As the water percolates through the bedrock, it carries away small parts of the rock with it. As the bedrock erodes, particles collect in the spaces it leaves. Over a period of time, a small depression is formed. It is at this point where the hole forms. The hole is usually bowl shaped and can be quite large. Sometimes the bedrock may collapse all of a sudden to form such a solution sinkhole and other times it happens over time.

The second kind of sinkholes are known as Cover Collapse sinkhole. These take place when the bedrock is covered by a deep layer of soil and earth. Once the bedrock begins to get eroded, crack start forming in the rocky areas around it. When this happens, a number of weak points begin to form in the layers of soil and strata above it. Finally, it comes to a point when the weak points become a large hole within the bedrock that cannot support the weight above it. The cover collapse usually happens in a sudden manner and can create large holes in a matter of minutes.

The last kind of sinkholes are known as Cover Subsidence Sinkhole. In this case, the hole is formed over a period of time. The bedrock here is covered by soil and materials which are not well knitted together. Areas that have soil comprising largely of clay or sand often face the occurrence of this hole. Once the bedrock starts to erode, the clay or sand starts permeating through the cracks and settles into the spaces left behind. Over time, this creates a cavity on the surface of the soil and not under it.

Lesson Plan: Here is a great lesson plan on the science of a sinkhole.

Lesson Plan: This is a fun lesson plan where kids can make a sinkhole in a cup.

Lesson Plan: Here is a great lesson plan on how sinkholes form.

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 are sinkholes? Sinkholes are pits in the ground that form in areas where water gathers without external drainage. Sinkholes mainly occur as water drains below ground. It can dissolve subterranean caverns, particularly in areas where the bedrock is made of water-soluble evaporate rocks such as salt or gypsum or of carbonate rocks such as limestone or dolomite.

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Karst is a geological system of rocks where water has eroded (dissolved) the bedrock. If it is very extensive, karst can be a geographical or topographical feature. It is classed as a badland if it difficult to travel through the environment, which it often is.

Almost always, karst is formed in carbonate rocks, such as limestone or dolomite. Since carbonate sedimentary rocks are very common, karst areas occur all over the world.

Many karst regions display distinctive surface features, with sinkholes being the most common. However, karst surface features may be absent where the soluble rock is mantled (covered), such as by a non-soluble rock strata on top of the carbonate strata. Some karst regions include thousands of caves, and the water is generally underground.

The world's largest karst area is the Nullarbor Plain, part of the area of flat, almost treeless, dry country of southern Australia. It is on the Great Australian Bight coast with the Great Victoria Desert to its north. It is the world's largest single exposure of limestone bedrock, and occupies an area of about 200,000 square kilometres (77,000 sq mi). At its widest point, it stretches about 1,100 kilometres (684 mi) from east to west across the border region between South Australia and Western Australia.

Many parts of the world suffer from sinkholes which form when karsts are underground. Beneath the flat surface of the land in Florida, Guatemala City and elsewhere are vast systems of limestone. Water running through the limestone is dissolving the limestone away, leaving huge caverns. Without warning, huge holes appear in the surface, causing great damage. Practically the whole of Florida is sitting on a gigantic karst system, as are several countries in Central America. The area round Tampa is especially at risk, and there is a huge karst system under Mexico City. According to a senior geochemist, there are as many as 15,000 sinkholes in Illinois.

The world's deepest sinkhole is China's Xiaozhai Tienkeng at 2172ft (662m).

The Qattara Depression in Egypt is part of the Libyan Desert. It is roughly 50 miles (80km) by 75 miles (121km) in surface area. It is the world's largest natural sinkhole. It lies below sea level and is covered with salt pans, sand dunes and salt marshes.

Related pages

Images for kids

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Karst is a geological system of rocks where water has eroded (dissolved) the bedrock. If it is very extensive, karst can be a geographical or topographical feature. It is classed as a badland if it difficult to travel through the environment, which it often is.

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sinkholes | science with dr karl | national geographic kids

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A sinkhole is a void in the ground caused by a collapse of the Earth’s surface layer usually when limestone and gypsum shifts from lots of moving water.

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What causes Sinkholes? | #aumsum #kids #science #education #children

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This DragonflyTV segment-set in southeast Minnesota, the sinkhole capital of the U.S.A.-demonstrates how and why sinkholes form, and illustrates the common characteristics of sinkholes.

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This DragonflyTV segment follows two girls as they walk the fault lines of San Francisco and learn that it is the movement of plates beneath the earth's surface that causes earthquakes. Available in both English and Spanish.

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This DragonflyTV segment demonstrates the forces necessary to produce a tornado as two children build their own tornado model.

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Most earthquakes and volcanic eruptions do not strike randomly but occur in specific areas, such as along plate boundaries. One such area is the circum-Pacific Ring of Fire, where the Pacific Plate meets many surrounding tectonic plates. The Ring of Fire is the most seismically and volcanically active zone in the world.Learn more: U.S.

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What is a fault and what are the different types?

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A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep.