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Volcanoes
(Volcanoes are not associated with weather, but instead are natural disasters.)

What is a volcano?
A volcano is a mountain that opens downward to a pool of molten rock below the surface of the earth. When pressure builds up, eruptions occur. Gases and rock shoot up through the opening and spill over or fill the air with lava fragments. Eruptions can cause lateral blasts, lava flows, hot ash flows, mudslides, avalanches, falling ash and floods. Volcano eruptions have been known to knock down entire forests. An erupting volcano can trigger tsunamis, flash floods, earthquakes, mudflows and rockfalls.

How are volcanoes formed?
Volcanoes are formed when magma from within the Earth's upper mantle works its way to the surface. At the surface, it erupts to form lava flows and ash deposits. Over time as the volcano continues to erupt, it will get bigger and bigger.

What are the different stages of volcanoes?
Scientists have categorized volcanoes into three main categories: active, dormant, and extinct. An active volcano is one which has recently erupted and there is a possibility that it may erupt soon. A dormant volcano is one which has not erupted in a long time but there is a possibility it can erupt in the future. An extinct volcano is one which has erupted thousands of years ago and there's no possibility of eruption.

Why do volcanoes erupt? The Earth's crust is made up of huge slabs called plates, which fit together like a jigsaw puzzle. These plates sometimes move. The friction causes earthquakes and volcanic eruptions near the edges of the plates. The theory that explains this process is called plate tectonics.

The theory of plate tectonics is a interesting story of continents drifting from place to place breaking apart, colliding, and grinding against each other. The plate tectonic theory is supported by a wide range of evidence that considers the earth's crust and upper mantle to be composed of several large, thin, relatively rigid plates that move relative to one another. The plates are all moving in different directions and at different speeds. Sometimes the plates crash together, pull apart or sideswipe each other. When this happens, it commonly results in earthquakes. What are plate tectonics?

Continental Drift: To see this animation again, just refresh this page! This animation shows you what our planet looked like millions of years ago and what it looks like now! (Graphic Credit: Geology Department at University of California, Berkeley)

There are more than 1500 active volcanoes on the Earth. We currently know of 80 or more which are under the oceans. Active volcanoes in the U.S. are found mainly in Hawaii, Alaska, California, Oregon and Washington.
How many volcanoes are there?

What are the different types of volcanoes?
Volcanoes are grouped into four types: cinder cones, composite volcanoes, shield volcanoes and lava volcanoes.

Cinder Cones

Cinder cones are circular or oval cones made up of small fragments of lava from a single vent that have been blown into the air, cooled and fallen around the vent.

Composite Volcanoes

Composite volcanoes are steep-sided volcanoes composed of many layers of volcanic rocks, usually made from high-viscosity lava, ash and rock debris. Mt. Rainier and Mount St. Helens are examples of this type of volcano.

Shield Volcanoes

Shield volcanoes are volcanoes shaped like a bowl or shield in the middle with long gentle slopes made by basaltic lava flows. Basalt lava flows from these volcanoes are called flood basalts. The volcanoes that formed the basalt of the Columbia Plateau were shield volcanoes.

Lava Volcanoes

Lava domes are formed when erupting lava is too thick to flow and makes a steep-sided mound as the lava piles up near the volcanic vent. The eruption of Mount St. Helens in 1980 was caused in part by a lava dome shifting to allow explosive gas and steam to escape from inside the mountain.

Magma is liquid rock inside a volcano. Lava is liquid rock (magma) that flows out of a volcano. Fresh lava glows red hot to white hot as it flows.

What is the difference between lava and magma?

Why does lava take a long time to cool down?
Lava cools slowly because lava is a poor conductor of heat. Lava flows slow down and thicken as they harden.
What is a pyroclastic flow?
A pyroclastic flow is a fluidized mixture of solid to semi-solid fragments and hot, expanding gases that flows down the sides of a volcano. These awesome features are heavier-than-air emulsions that move much like a snow avalanche, except that they are fiercely hot, contain toxic gases, and move at phenomenal, hurricane-force speeds. They are the most deadly of all volcanic phenomena.

What is lahar?
A lahar is a type of mudflow or debris flow composed of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. It is very dangerous because it's consistency and the way it acts is very much like cement. It is liquid when it's moving, but when it stops, it solidifies. This can cause just as much devastation as lava itself.
What is pumice?
Pumice is a light, porous volcanic rock that forms during explosive eruptions. It resembles a sponge because it consists of a network of gas bubbles frozen amidst fragile volcanic glass and minerals. All types of magma (basalt, andesite, dacite, and rhyolite) will form pumice.

What is the largest active volcano?
The world's largest, active volcano is Mauna Loa in Hawaii, where famous coffee is grown in the rich volcanic soils. Mauna Loa is 13,677 feet above sea level. From its base below sea level to its summit, Mauna Loa is taller than Mount Everest.

What is the Ring of Fire?

The Pacific Ring of Fire is an area of frequent earthquakes and volcanic eruptions encircling the basin of the Pacific Ocean. The Ring of Fire has 452 volcanoes and is home to over 50% of the world's active and dormant volcanoes. Ninety percent of the world's earthquakes and 81% of the world's largest earthquakes occur along the Ring of Fire.

When did Mount St. Helens erupt?
On May 18, 1980, Mount St. Helens erupted. It's located in southwestern Washington State in the Cascade Range. The blast was heard as far away as Montana, Idaho, Canada and California. Fifty-seven people died and the eruption caused $1.2 billion in damage.

What are some other notable volcano eruptions?
Krakatoa was a dormant volcano in Indonesia, which awakened and produced one of the biggest volcanic eruptions in 1883. So massive was the eruption that the sound of it was heard as far away as Australia. It's widely reported as the loudest sound heard in recorded history. The Krakatoa eruption created a huge amount of ash cloud which covered the Earth and reduced global temperatures for 5 years! A total of 40,000 people died in that explosion and an entire chain of the volcanic island was destroyed. For more info: Click Here!

Mount Pelee was a dormant volcano situated in the Caribbean island of Martinique. In 1902, it erupted in a massive horizontal explosion sending huge clouds of ash released towards the nearby town of Saint-Pierre. The side of the volcano exploded and lava flowed straight into the town, killing 30,000 people in a matter of minutes. It is regarded as one of the biggest and most devastating volcanic eruptions of the 20th century, a benchmark for future eruptions.

Mount Fujiyama, also popularly known as Mount Fuji, is an active volcano which last erupted in 1708. It is incidentally the tallest mountain in Japan. If you are visiting Tokyo, the capital of Japan, look in the west on a clear day and you will be able to see Mount Fuji. It is an iconic volcano. Mount Fuji is 3,776 meters high and it is snow clad throughout the year, with five lakes surrounding it. Currently in a state of dormancy, there has not been any eruption reported for more than 300 years. The last known eruption lasted for about 3 weeks during which it covered the surrounding villages with ash and cinders. Mount Fuji is now a popular tourist location with a large number of climbers actively scaling the mountain top.

What is a tsunami?
A tsunami is a large ocean wave usually caused by an underwater earthquake or a volcanic explosion. Tsunamis are NOT tidal waves. Tidal waves are caused by the forces of the moon, sun, and planets upon the tides, as well as the wind as it moves over the water. With typical waves, water flows in circles, but with a tsunami, water flows straight. This is why tsunamis cause so much damage!

Know the Lingo
MAGMA - Magma is the liquid rock inside a volcano.

LAVA - Lava is the liquid rock (magma) that flows out of a volcano. Lava glows red hot to white hot as it flows.

ACTIVE VOLCANO - An active volcano is one that erupts regularly.
Volcano Safety Tips
PLAN FOR A VOLCANO: First of all, have a disaster plan and know whether or not you are at risk for danger. Be prepared for mudslides, flash floods, earthquakes, ash falling, acid rain and tsunamis. Prepare a disaster supplies kit for your home and car. Include a first aid kit, canned food and a can opener, bottled water, battery-operated radio, flashlight, protective clothing, dust mask, goggles and sturdy shoes. Don't forget, know all of your evacuation routes. DURING A VOLCANO: Follow the evacuation order issued by authorities. Avoid areas downwind and river valleys downstream of the volcano. If your caught indoors, close all windows and doors, put machinery inside a barn, and bring animals inside. If you're trapped outdoors, seek shelter indoors. If you're caught in falling rocks, roll into a ball and protect your head. If you're caught near a stream, be aware of mudflows and move to higher ground. Protect yourself when ash falls by wearing long-sleeved shirts and long pants. Use goggles to protect your eyes. Wear a dust mask and keep car engines off.
DORMANT VOLCANO - A dormant volcano is one that has not erupted for many years, although there is still some activity deep inside. AFTER A VOLCANO: Cover you mouth and nose. Volcanic ash can irritate your respiratory system. Wear goggles and protect your eyes. Keep your skin covered. Clear roofs of ash, because the ash is very heavy and can cause the building to collapse.
Volcano Activities
Lesson Plan: Here are great lesson plans on learning more about volcanoes. These are great lesson plans for elementary school students.
EXTINCT VOLCANO - An extinct volcano is a volcano that is no longer active.Volcano Experiment: Here is an experiment on how to make a soda bottle volcano with Mentos.
Volcano Experiment: Here is another experiment on how to make a baking soda volcano.
GEYSERS - Geysers are springs that throw boiling water high in the air. They are caused by volcanic heat warming trapped ground water.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.

ASH - Ash are very small fragments of lava or rock blasted into the air by volcanic explosions.

PUMICE - It is a light-colored volcanic rock containing lots of bubbles from trapped gases.

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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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An avalanche happens when a layer of snow becomes loose and slides downhill. Thousands of avalanches occur every winter in the mountains and are usually triggered by people. Avalanches are caused by these four factors: a steep slope, a snow cover, a weak layer in the snow cover and a trigger such as a snowboarder or skier.

Avalanches and Snowslides - Three Main Types

Powder Avalanches - An increasing volume of powdered snow is thrown into the air, charging down the slope like a dense cloud. It can reach speeds of 250 mph (400 kph) and can flatten anything in its path.

Wet Snow Avalanches - When the temperature warms up, snow weakens and a wet snow avalanche can happen. The snow spreads as it slowly slides. Once it stops, it settles like concrete so buried victims can't move or breathe.

Slab Avalanches - These are the most common and are usually triggered by skiers. When layers of snow don't cling together, a trigger such as the weight and tracks of a skier or snowboarder, will cause the top layer to slide. There is little chance of escaping the moving slab as it breaks and carries a victim down the slope.

Avalanche formation

Avalanches and Snowslides - Outrunning a Slide

Don't bother trying to outrun an avalanche. You won't make it. Dry slab avalanches usually cruise down a slope around 60-80 mph (97-130 kph.) They can reach these speeds about five seconds after they fracture. Wet avalanches are much slower at about 20 mph (32 kph) but it's still a miracle to outrun one.

The Most Dangerous Avalanche

The most dangerous is a dry slab avalanche - it causes the most deaths. Imagine a dinner plate sliding off a table. When the plate shatters and keeps sliding, the food on the plate hardly stands a chance. The slab shatters like glass with the victim in the middle - escape is rare.

Slab Avalanche

Avalanche Facts

This usually has a lot to do with luck. But avoiding potential avalanches has to do with using your brains. Here are some avalanche facts to consider:

Your chances of surviving an avalanche are around 80% if you use/carry the proper equipment (beacons, shovel, probes, etc.).

Without proper equipment your survival chances are less than three percent.

Check the conditions and the slope stability before skiing or boarding in avalanche territory.

Skiing or boarding out of bounds increases your chances of being caught in a snow slide.

If you're caught in an avalanche, swim with the avalanche to try and stay on top.

Related Stories:

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An avalanche happens when a layer of snow becomes loose and slides downhill. Thousands of avalanches occur every winter in the mountains and are usually triggered by people. Avalanches are caused by these four factors: a steep slope, a snow cover, a weak layer in the snow cover and a trigger such as a snowboarder or skier.

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Falling masses of snow and ice, avalanches pose a threat to anyone on snowy mountainsides. Beautiful to witness from afar, they can be deadly because of their intensity and seeming unpredictability.

Humans trigger 90 percent of avalanche disasters, with as many as 40 deaths in North America each year. Most are climbers, skiers, and snowmobilers. Learning about avalanches, and the conditions that cause them, can help people recreate more safely in the backcountry.

Types of avalanches

The recipe for an avalanche may seem simple: a mountain slope and a thick layer of snow. But Simon Trautman, an avalanche specialist at the U.S. Forest Service's National Avalanche Center and Northwest Avalanche Center in Washington, says it's actually a trifecta that causes avalanches: terrain, snowpack, and weather conditions. Avalanches do occur naturally, but when you add humans into the mix, they can be deadly, says Trautman.

Avalanches come in many shapes and sizes. Many are small slides of powdery snow that move as a formless mass downslope. Outdoor recreationists often trigger these small "sluffs," as well as more medium-sized avalanches.

Disastrous avalanches occur when massive slabs of snow break loose from a mountainside. The mass of snow shatters like broken glass as it races downhill. These hazards can travel as fast as cars on a freeway, up to 100 miles per hour, says Trautman.

Snow slides can start on mountain slopes with at least a 30-degree incline, but they occur most frequently on slopes of 35-50 degrees. Although avalanches need a slope to start, large avalanches accelerate downhill with sufficient momentum to cross flat terrain for short distances.

In some cases, a large chunk of ice or small glacier breaks off a mountainside, gathering snow and momentum and rushing down in a dangerous steamroll. One of the most deadly avalanches on Mount Everest, which killed 16 Sherpas, occurred when an ice mass the weight of 657 buses plummeted down on top of hikers.

Features of avalanches

Avalanches contain three main features: the starting zone, the avalanche track, and the runout zone. Avalanches launch from the starting zone. That's often the most unstable part of the stope, and generally higher on the mountain.

Once the avalanche starts to slide, it continues down the avalanche track, the natural path it follows downhill. After avalanches, large clearings or missing chutes of trees provide clues to an avalanche's trajectory.

The avalanche finally comes to a stop at the bottom of a slope, in the runout zone, where the snow and debris pile up.

What conditions cause an avalanche?

Avalanches are most common during the winter, December to April in the Northern Hemisphere, but they do occur year-round.

To get an avalanche, you need a surface bed of snow, a weaker layer that can collapse, and an overlaying snow slab. The highest risk period is during and immediately after a snow storm. Underlying snowpack, overloaded by a quick deluge of snow, can cause a weak layer beneath the slab to fracture naturally.

Human-triggered avalanches start when somebody walks or rides over a slab with an underlying weak layer. The weak layer collapses, causing the overlaying mass of snow to fracture and start to slide. Earthquakes can also trigger strong avalanches.

By digging a snow pit or profile, scientists can look at the composition of different snow layers that formed during a season, sort of like looking at the layers of a cake. The size and shape of the snowflakes in each layer provide clues about the weather events that occurred: big dumps of snow, drought, rain, a hard freeze, or loose, powdery snow. Larger, looser snow crystals are weaker, because there are fewer points they can touch to interact with the other snow layers. The interaction of the snow layers can help predict the chances of an avalanche.

"Snow is an incredibly dynamic and complicated medium, which means avalanches are the same," says Trautman. He emphasizes that conditions can change rapidly with the weather, and this can be deadly.

Slopes shaded from direct sun stay cooler, preventing bonding between snow layers and leading to more avalanches in cold conditions. Conversely, during the spring, sunny mountainsides have a higher risk for avalanches because of rapid warming and melting. The number of "wet snow" slides could increase in the future with climate change, experts warn.

Precipitation type and intensity, temperature, wind, slope steepness and orientation (the direction it faces), terrain, vegetation, and general snowpack conditions can influence whether and how snow moves down a slope. Moving across the terrain, slight changes in slope or how the mountainside is oriented towards the sun can create drastically different conditions.

Take avalanche danger seriously

The Forest Service runs 14 backcountry avalanche centers in the United States to provide information for people recreating in snowy wilderness areas. Forecasters use four main elements to describe conditions, assign a danger level, and help recreators make the best decisions in the backcountry.

Field teams at avalanche centers document the snowpack-the thickness and type of snow layers-and combine those data with weather conditions to estimate danger levels. The forecasts take into account the potential type and size of an avalanche, the likelihood it will occur, and the location.

In some instances, forest rangers can blast cannons and other military artillery at unstable snowpack to trigger avalanches in a safe and controlled manner-when people aren't present.

Before entering the backcountry, check online forecasts for the danger level in that area. Each mountain range has unique snow properties and therefore, avalanche risks, so checking your specific region is critical. New Zealand, Canada, and Europe also maintain year-round forecasts of avalanche danger for specific peaks and wilderness areas.

Experts recommend hiking and travelling earlier in the day. Weather conditions can change rapidly, and warming during the day creates more unstable snowpack with a higher risk for avalanches.

Education and proper training on avalanches can help prepare you. Heed all warnings and signs. Some accidents have been traced to people avoiding warnings due to psychological traps, like desiring the ultimate ski slope, untouched by humans.

Constant vigilance when you are outside can help avoid causing or getting swept up in avalanches, but even trained experts can be become victims. Be aware of the weather and terrain, and know your comfort level before you embark on an adventure. ( Read more about avalanche safety tips.)

If caught in an avalanche, try to get off the slab. In best case scenarios, this is difficult. Skiers and snowboarders can head at a 45-degree angle downhill to gather speed and veer left or right out of the slide path. Snowmobilers can punch the throttle to power out of harm's way.

No escape? Reach for a tree. No tree? Swim hard. The human body is denser than avalanche debris and will sink quickly. As the slide slows, clear air space to breathe. Then punch a hand skyward.

Once the avalanche stops, it settles like concrete, making body movement nearly impossible. Wait-and hope-for a rescue. ( Read about rescue dogs, trained to locate and dig out avalanche victims.)

"Learning about avalanches really helps people decide when and where, and how to recreate," said Trautman. "We shouldn't all be terrified of this stuff, but we should take it seriously. It's supposed to be fun!"

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Falling masses of snow and ice, avalanches pose a threat to anyone on snowy mountainsides. Beautiful to witness from afar, they can be deadly because of their intensity and seeming unpredictability. Humans trigger 90 percent of avalanche disasters, with as many as 40 deaths in North America each year.

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An avalanche is a phenomenon of nature. It is linked to snow. When there is too much snow on a mountain, some of the snow may fall, causing damage to things in its path. This is called an avalanche. People talk about avalanches because they may be dangerous to skiers and other people doing winter sports.

Large avalanches may carry stones, boulders and trees with them. They may bury people under them. If the people are not found rapidly enough by rescue teams they will die of suffocation (not getting enough air) or of hypothermia (freezing cold).

The chance of surviving an avalanche is as follows:

92% if found within 15 minutes

30% if found within 35 minutes (victims die of suffocation)

nearly zero after two hours (victims die of injuries and hypothermia)

Most avalanches occur spontaneously during storms under increased load due to snowfall. The second largest cause of natural avalanches is metamorphic changes in the snowpack such as melting due to the sun. Other natural causes include rain, earthquakes, rockfall and icefall. Artificial triggers of avalanches include skiers, snowmobiles, and controlled explosive work. Contrary to popular belief, avalanches are not triggered by loud sound; the pressure from sound is orders of magnitude too small to trigger an avalanche.

Avalanche initiation can start at a point with only a small amount of snow moving initially; this is typical of wet snow avalanches or avalanches in dry unconsolidated snow. However, if the snow has sintered into a stiff slab overlying a weak layer then fractures can propagate very rapidly, so that a large volume of snow, that may be thousands of cubic meters, can start moving almost simultaneously.

A snowpack will fail when the load exceeds the strength. The load is straight forward; it is the weight of the snow. However, the strength of the snowpack is much more difficult to determine and is extremely heterogenous. It varies in detail with properties of the snow grains, size, density, morphology, temperature, water content; and the properties of the bonds between the grains. These properties may all metamorphose in time according to the local humidity, water vapour flux, temperature and heat flux. The top of the snowpack is also extensively influenced by incoming radiation and the local air flow. One of the aims of avalanche research is to develop and validate computer models that can describe the evolution of the seasonal snowpack over time. A complicating factor is the complex interaction of terrain and weather, which causes significant spatial and temporal variability of the depths, crystal forms, and layering of the seasonal snowpack.

Slab avalanches

Slab avalanches form frequently in snow that has been deposited, or redeposited by wind. They have the characteristic appearance of a block (slab) of snow cut out from its surroundings by fractures. Elements of slab avalanches include the following: a crown fracture at the top of the start zone, flank fractures on the sides of the start zones, and a fracture at the bottom called the staunchwall. The crown and flank fractures are vertical walls in the snow delineating the snow that was entrained in the avalanche from the snow that remained on the slope. Slabs can vary in thickness from a few centimetres to three metres. Slab avalanches account for around 90% of avalanche-related fatalities in backcountry users.

Powder snow avalanches

The largest avalanches form turbulent suspension currents known as powder snow avalanches or mixed avalanches. These consist of a powder cloud, which overlies a dense avalanche. They can form from any type of snow or initiation mechanism, but usually occur with fresh dry powder. They can exceed speeds of 300 kilometres per hour (190 mph), and masses of 10,000,000 tonnes (10,000,000 long tons; 10,000,000 short tons); their flows can travel long distances along flat valley bottoms and even uphill for short distances.

Wet snow avalanches

In contrast to powder snow avalanches, wet snow avalanches are a low velocity suspension of snow and water, with the flow confined to the track surface (McClung, first edition 1999, page 108). The low speed of travel is due to the friction between the sliding surface of the track and the water saturated flow. Despite the low speed of travel (~10-40 km/h), wet snow avalanches are capable of generating powerful destructive forces, due to the large mass and density. The body of the flow of a wet snow avalanche can plough through soft snow, and can scour boulders, earth, trees, and other vegetation; leaving exposed and often scored ground in the avalanche track. Wet snow avalanches can be initiated from either loose snow releases, or slab releases, and only occur in snow packs that are water saturated and isothermally equilibrated to the melting point of water. The isothermal characteristic of wet snow avalanches has led to the secondary term of isothermal slides found in the literature (for example in Daffern, 1999, page 93). At temperate latitudes wet snow avalanches are frequently associated with climatic avalanche cycles at the end of the winter season, when there is significant daytime warming.

Avalanche pathway

As an avalanche moves down a slope it follows a certain pathway that is dependent on the slope's degree of steepness and the volume of snow/ice involved in the mass movement. The origin of an avalanche is called the Starting Point and typically occurs on a 30-45 degree slope. The body of the pathway is called the Track of the avalanche and usually occurs on a 20-30 degree slope. When the avalanche loses its momentum and eventually stops it reaches the Runout Zone. This usually occurs when the slope has reached a steepness that is less than 20 degrees. These degrees are not consistently true due to the fact that each avalanche is unique depending on the stability of the snowpack that it was derived from as well as the environmental or human influences that triggered the mass movement.

In many areas, regular avalanche tracks can be identified and precautions can be taken to minimise damage, such as the prevention of development in these areas. To mitigate the effect of avalanches the construction of artificial barriers can be very effective in reducing avalanche damage. There are several types: One kind of barrier (snow net) uses a net strung between poles that are anchored by guy wires in addition to their foundations. These barriers are similar to those used for rockslides. Another type of barrier is a rigid fence-like structure (snow fence) and may be constructed of steel, wood or pre-stressed concrete.

Early warning systems

Warning systems can detect avalanches which develop slowly, such as ice avalanches caused by icefalls from glaciers. Interferometric Radars, high-resolution Cameras, or motion sensors can monitor instable areas over a long term, lasting from days to years. Experts interpret the recorded data and are able to recognize upcoming ruptures in order to initiate appropriate measures. Such systems (e.g. the monitoring of the Weissmies glacier in Switzerland) can recognize events several days in advance.

Alarm systems

Modern radar technology enables the monitoring of large areas and the localization of avalanches at any weather condition, by day and by night. Complex alarm systems are able to detect avalanches within a short time in order to close (e.g. roads and rails) or evacuate (e.g. construction sites) endangered areas. An example of such a system is installed on the only access road of Zermatt in Switzerland. Two radars monitor the slope of a mountain above the road. The system automatically closes the road by activating several barriers and traffic lights within seconds such that no persons are harmed.

European avalanche risk table

In Europe, the avalanche risk is widely rated on the following scale, which was adopted in April 1993 to replace the earlier non-standard national schemes. Descriptions were last updated in May 2003 to enhance uniformity pdf.

Risk Level

Snow Stability

Avalanche Risk

1 - Low

Snow is generally very stable.

Avalanches are unlikely except when heavy loads [2] are applied on a very few extreme steep slopes. Any spontaneous avalanches will be minor (sluffs). In general, safe conditions.

2 - Limited

On some steep slopes the snow is only moderately stable [1]. Elsewhere it is very stable.

Avalanches may be triggered when heavy [2] loads are applied, especially on a few generally identified steep slopes. Large spontaneous avalanches are not expected.

3 - Medium

On many steep slopes [1] the snow is only moderately or weakly stable.

Avalanches may be triggered on many slopes even if only light loads [2] are applied. On some slopes, medium or even fairly large spontaneous avalanches may occur.

4 - High

On most steep slopes [1] the snow is not very stable.

Avalanches are likely to be triggered on many slopes even if only light loads [2] are applied. In some places, many medium or sometimes large spontaneous avalanches are likely.

5 - Very High

The snow is generally unstable.

Even on gentle slopes, many large spontaneous avalanches are likely to occur.

[1] Stability:

Generally described in more detail in the avalanche bulletin (regarding the altitude, aspect, type of terrain etc.)
[2] additional load:

heavy: two or more skiers or boarders without spacing between them, a single hiker or climber, a grooming machine, avalanche blasting.

light: a single skier or snowboarder smoothly linking turns and without falling, a group of skiers or snowboarders with a minimum 10 m gap between each person, a single person on snowshoes.

Gradient:

gentle slopes: with an incline below about 30°.

steep slopes: with an incline over 30°.

very steep slopes: with an incline over 35°.

extreme steep slopes: extreme in terms of the incline (over 40°), the terrain profile, proximity of the ridge, smoothness of underlying ground.

Avalanche size:
Notable avalanches

Two avalanches occurred in March 1910 in the Cascade and Selkirk Mountain ranges; On 1 March the Wellington avalanche killed 96 in Washington state, United States. Three days later 62 railroad workers were killed in the Rogers Pass avalanche in British Columbia, Canada.

During World War I, an estimated 40,000 to 80,000 soldiers died as a result of avalanches during the mountain campaign in the Alps at the Austrian-Italian front, many of which were caused by artillery fire. Some 10,000 men, from both sides, died in avalanches in December 1916.

In the northern hemisphere winter of 1950-1951 approximately 649 avalanches were recorded in a three-month period throughout the Alps in Austria, France, Switzerland, Italy and Germany. This series of avalanches killed around 265 people and was termed the Winter of Terror.

A mountain climbing camp on Lenin Peak, in what is now Kyrgyzstan, was wiped out in 1990 when an earthquake triggered a large avalanche that overran the camp. Forty-three climbers were killed.

In 1993, the Bayburt Üzengili avalanche killed 60 individuals in Üzengili in the province of Bayburt, Turkey.

A large avalanche in Montroc, France, in 1999, 300,000 cubic metres of snow slid on a 30° slope, achieving a speed in the region of 100 km/h (62 mph). It killed 12 people in their chalets under 100,000 tons of snow, 5 meters (16 feet) deep. The mayor of Chamonix was convicted of second-degree murder for not evacuating the area, but received a suspended sentence.

The small Austrian village of Galtür was hit by the Galtür avalanche in 1999. The village was thought to be in a safe zone but the avalanche was exceptionally large and flowed into the village. Thirty-one people died.

On 1 December 2000, the Glory Bowl Avalanche formed on Mt. Glory which is located within the Teton Mountain Range in Wyoming, United States. Joel Roof was snowboarding recreationally in this backcountry, bowl-shaped run and triggered the avalanche. He was carried nearly 2,000 feet to the base of the mountain and was not successfully rescued.

Avalanches on the planet Mars

Images for kids

A cornice of snow about to fall. Cracks in the snow are visible in area (1). Area (3) fell soon after this picture was taken, leaving area (2) as the new edge.

After digging a snow pit, it is possible to evaluate the snowpack for unstable layers. In this picture, snow from a weak layer has been easily scraped away by hand, leaving a horizontal line in the wall of the pit.

In Spanish: Alud para niños

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What is an earthquake?
Earthquakes are the shaking, rolling or sudden shock of the earth's surface. They are the Earth's natural means of releasing stress. More than a million earthquakes rattle the world each year. The West Coast is most at risk of having an earthquake, but earthquakes can happen in the Midwest and along the East Coast. Earthquakes can be felt over large areas although they usually last less than one minute. Earthquakes cannot be predicted - although scientists are working on it!

Click Here to learn more about earthquakes from USGS.

What causes an earthquake?
There are about 20 plates along the surface of the earth that move continuously and slowly past each other. When the plates squeeze or stretch, huge rocks form at their edges and the rocks shift with great force, causing an earthquake. Think of it this way: Imagine holding a pencil horizontally. If you were to apply a force to both ends of the pencil by pushing down on them, you would see the pencil bend. After enough force was applied, the pencil would break in the middle, releasing the stress you have put on it. The Earth's crust acts in the same way. As the plates move they put forces on themselves and each other. When the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy which moves through the Earth in the form of waves, which we feel and call an earthquake. (Graphic Credit: Wheeling Jesuit University/NASA Classroom of the Future)

Click Here to see an animation of an earthquake. It's great for kids, because they get to see how it actually happens!

What is a fault?
A fault is an area of stress in the earth where broken rocks slide past each other, causing a crack in the Earth's surface. There are the major types of faults: dip-slip normal, dip-slip reverse, strike-slip, and oblique-slip.

What are plate tectonics?
The theory of plate tectonics is a interesting story of continents drifting from place to place breaking apart, colliding, and grinding against each other. The plate tectonic theory is supported by a wide range of evidence that considers the earth's crust and upper mantle to be composed of several large, thin, relatively rigid plates that move relative to one another. (See plate tectonic graphic above.) The plates are all moving in different directions and at different speeds. Sometimes the plates crash together, pull apart or sideswipe each other. When this happens, it commonly results in earthquakes.

Continental Drift: To see this animation again, just refresh this page! This animation shows you what our planet looked like millions of years ago and what it looks like now! (Graphic Credit: Geology Department at University of California, Berkeley)

What is a seismograph?
A seismograph is an instrument used for recording the intensity and duration of an earthquake.

Click Here to calculate the strength of earthquakes!

What is a tsunami? A tsunami is a large ocean wave usually caused by an underwater earthquake or a volcanic explosion. Tsunamis are NOT tidal waves. Tidal waves are caused by the forces of the moon, sun, and planets upon the tides, as well as the wind as it moves over the water. With typical waves, water flows in circles, but with a tsunami, water flows straight. This is why tsunamis cause so much damage!

Know the Lingo

EPICENTER - The point on the earth's surface directly above the source of the earthquake.

SEISMIC WAVES - The energy created by the quake travels in waves from the epicenter, where they are the strongest. The waves shake buildings, structures and the earth vertically, causing them to move horizontally!

RICHTER SCALE - A measurement of an earthquake's intensity. Each one-point increase on the scale indicates ten times the amount of shaking and 33 times the amount of energy. The energy released by a large earthquake may be equal to 10,000 times the energy of the first atomic bomb.

4

Minor Earthquake

5

Moderate Earthquake

6

Strong Earthquake

7

Major Earthquake

8

Great Earthquake

Richter Scale

Earthquake Safety Tips
BEFORE AN EARTHQUAKE: Have a disaster plan. Emergency preparedness can save lives. Choose a safe place in every room. It's best to get under a sturdy piece of furniture like a table or a desk where nothing can fall on you. Practice DROP, COVER AND HOLD ON! Drop under something sturdy, hold on, and protect your eyes by pressing your face against your arm. If you live in an earthquake prone area, bolt tall furniture to the wall and install strong latches to cupboards. Prepare a first aid kit for your home. By taking special precautions and checking for hazards before a disaster strikes, you will be much more likely to stay safe. DURING AN EARTHQUAKE: DROP, COVER AND HOLD ON! Stay indoors until the shaking stops. Stay away from windows. If you're in bed, hold on and stay there, protecting your head with a pillow. If you're outdoors, find a clear spot away from buildings, trees and power lines. Then, drop to the ground. If you're in a car, slow down and drive to a safe place. Stay in the car until the shaking stops.

AFTER THE SHAKING STOPS: Check for injuries. Inspect your home for damage. Eliminate fire hazards, so turn off the gas if you think its leaking. Expect aftershocks. Each time you feel one, DROP, COVER AND HOLD ON.
Earthquake Activities
Lesson Plan: Here is a great lesson plan on learning about how thrust faults are responsible for the uplift of many mountain ranges across the world, including the Los Angeles Basin. This is a great lesson plan for middle and high school students.

Lesson Plan: Here is a great lesson plan keeping track of earthquakes around the world. In this activity, kids keep a record of the location of earthquakes for a week and learn about plate tectonics.

Earthquake Experiment: Here is a great experiment that explains how to prepare for an earthquake.Science Fair Ideas: Here is a list of science fair project ideas that deal with 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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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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Kid's learn about the science of earthquakes. What causes them and where they happen.

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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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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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Whenever a large group or rocks tumbles down a , geologists call it a landslide. When huge amounts of snow rush down the of a mountain, scientists call it an avalanche. So what do you call it when a huge of mud travels down a ? You guessed it! A mudslide, of course!

Mudslides occur when a large amount of water causes the rapid of on a steep . Rapid snowmelt at the top of a mountain or a period of rainfall can trigger a mudslide, as the great volume of water mixes with and causes it to and move downhill.

A mudslide can vary from very watery mud to thick mud with tons of , including large boulders, trees, and even cars or houses. Mudslides are responsible for many deaths and millions of dollars in property damage every year.

If you've ever stepped in mud, you know it can be very thick and . It might be hard to imagine such mud rushing downhill at a great speed in order to do much damage. Don't be fooled, though! Mudslides usually contain a lot of water, and thus act more like a than a landslide. Mudslides have been known to rush downhill at speeds up to 50 miles per hour, laying waste to everything in the way.

For example, on December 14, 1999, a mudslide in Vargas, Venezuela, affected over 37 miles of Venezuelan coastline. Some experts estimated that up to 30,000 people died as a result of the mudslide, which resulted in damages of over $3 billion.

When discussing mudslides, experts will use certain special terms, including main , shelves, and the "." The main is the original area where the mudslide began. The "," on the other hand, is the last area affected by the mudslide. Shelves are areas where a mudslide's path crosses hills or natural drops, creating large dips. A large mudslide can have multiple shelves.

Mudslides often occur in areas with steep slopes or at the bottom of slopes or canyons. Mountainous areas that have been altered to build homes and roads are often to mudslides. When human actions or natural events, such as wildfires, increase in an area, mudslides can be a natural result.

To protect yourself from mudslides, know the area in which you live. Have landslides or mudslides occurred before? If so, they can happen again. During periods of heavy rain, stay tuned to weather stations for alerts. If a mudslide warning is issued, make sure you can get to a safe area. High ground away from the path of a mudslide is where you want to be if a mudslide is .

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Today's Wonder of the Day mixes a lot of dirt with a lot of water!

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The Forces that Change the Face of Earth - Earth's Changing Surface - Beyond Penguins and Polar Bears

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In the Arctic and sub-Arctic, glacial erosion has shaped much of the landscape. Glaciers primarily erode through plucking and abrasion. Plucking occurs as a glacier flows over bedrock, softening and lifting blocks of rock that are brought into the ice.

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Copyright © 2010 The Kids Ecology Corps All rights reserved. | Sitemap | Legal | A PaperStreet Web Design | Files Login | Board Member Login

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Acid rain is rain that is unusually acidic. The acids are made when certain gases are carried high into the sky and react with the water in the atmosphere.

Acid rains can be harmful to plants, animals, and humans.

Robert Angus Smith is credited with the term "acid rain." In 1852, he showed the relationship between acid rain and atmospheric pollution in Manchester.

Although some natural gases, such as carbon dioxide, and gases from volcanoes can cause acid rain, it is now believed that mankind causes most acid rain. When people began building and using factories and power stations, they burned coal or oil. These compounds have sulfur in them that releases into the air, mixes with other elements, and produces acid rain.

Since the 1970s, governments have tried to clean smoke from factories and power stations to keep too much sulfur from rising into the atmosphere. This has had good results, but it is expensive.

In 2001, Great Britain still produced about five million tonnes (metric tons) of these gases every year, while China produced 18 million tonnes. The United States produced more than 20 million tonnes, but in 2010 that number fell to 8.1 million.

Adverse effects

Effects on lake ecology

The pH level in lakes needs to be correct for fish to be able to survive, and acid rain can affect a lake's pH level. If there is too much acid in the water several things can happen:

The enzymes that help fish larvae to hatch will not be produced.

Aluminum travels more easily through water, causing fish to make more mucus around their gills. This makes it harder for fish to breathe.

Phytoplankton will not grow well and the animals that feed on it would suffer.

Effects on soil biology

Acid rain can damage soil by killing microbes that are needed in the soil. The hydrogen ions of acid rain also allow toxins to move in the soil and take away nutrients that the soil needs. Forests usually are the home to fungi, but acid rain changes the soil, making it more filled with bacteria. Many trees in the forest depend on the fungi for water and minerals, while the fungi take carbohydrates from the trees. This symbiotic relationship, called mycorriza, can be destroyed by acids.

Other adverse effects

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Acid rain affects both living and non-living things. The leaves and roots of trees are damaged, making them less able to make food ( photosynthesis) and absorb nutrients. Toxic ions released due to acid rain are dangerous to humans. It is believed that copper (mobilized by acids) has caused outbreaks of diarrhea in young children. Statues and other ancient structures have also been harmed by acid rain.

Prevention methods

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In the U.S., the method for keeping sulfur from escaping into the air from the smokestacks of factories is called Flue Gas Desulfurization (FGD). One popular example is a wet scrubber, which pulls the gases from the stack into a tower and cleans them using lime or limestone. This changes the form of the chemical into a calcium sulfate that can be taken out of the scrubber. Sometimes the sulfates are sold to chemical companies. Other times, they are put in a landfill.

Some people do not want power generation to be controlled because they feel that pollution is a natural consequence of factories and power stations. They believe that if the pollution is not handled properly, it could be dangerous. Others install pollution controls for the benefits that they will receive from them.

Interesting facts about acid rain

Acid rain is a result of gases mixing with water high in the atmosphere.

Sulfur dioxide is released into the air by machines, houses, and vehicles and is the main chemical that creates acid rain.

Acid rain makes it more difficult for aquatic animals to survive.

Acid rain can damage the soil and the plants that live in it.

There are ways to prevent so much sulfur dioxide from escaping into the air. Many companies install pollution-controlling machinery in their factories.

Images for kids

Since 1998, Harvard University wraps some of the bronze and marble statues on its campus, such as this " Chinese stele", with waterproof covers every winter, in order to protect them from corrosion caused by acid rain and acid snow

In Spanish: Lluvia ácida para niños

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Let's say you made a cake and left it outside. What would happen? Maybe it would dry up and crack in the hot sun. Or perhaps rain would wash it away. If it froze, it might crack too. This process would probably take just a few days.

The Earth - and the rocks on the Earth - is a bit like that cake. The surface of the Earth is constantly being changed due to weathering processes. This process can take millions of years or happen relatively quickly.

Fun Facts about Weathering for Kids

Rain is mildly acidic and it slowly eats away rocks. Rain slowly dissolves limestone. It turns the feldspar in granite into soft clay. The remaining quartz crystals are often crushed into grains of sand.

Plants and microbes also attack rocks. All living things need elements, such as copper, potassium and iron, as nutrients. These minerals are found within rocks. Lichens grow on rocks and release acids to dissolve the minerals in them. Plant roots slowly grow into rocks, forcing them apart.

In cold areas, water seeps into cracks in the rocks during the day. At night, the water freezes and expands, cracking the rocks even more. This continual freeze and thaw cycle causes rocks to splinter and break into small pieces.

In the desert, rocks expand during the heat of the day and contract at night when temperatures cool. Sheets of rock slowly flake away.

Weathering Vocabulary

Learn More All About Weathering

Check out this cool video about Weathering for kids:

This video explains the factors and the process of weathering.

Weathering Q&A

Question: How are the types of weathering described?

Answer: Chemical weathering occurs when a chemical, such as acid rain, breaks down rocks. Mechanical weathering is the process of weathering through external forces, such as freeze and thaw cycles. When plants or microbes break down rocks, the process is known as organic weathering.

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

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Let's say you made a cake and left it outside. What would happen? Maybe it would dry up and crack in the hot sun. Or perhaps rain would wash it away. If it froze, it might crack too. This process would probably take just a few days.

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Erosion is a process where natural forces like water, wind, ice, and gravity wear away rocks and soil. It is a geological process, and part of the rock cycle. Erosion occurs at the Earth's surface, and has no effect on the Earth's mantle and core.

Most of the energy that makes erosion happen is provided by the Sun. The Sun's energy causes the movement of water and ice in the water cycle and the movement of air to create wind.

Erosion can cause problems that affect humans. Soil erosion, for example, can create problems for farmers. Soil erosion can remove soil, leaving a thin layer or rocky soil behind. Erosion can also cause problems for humans by removing rocks or soil that support buildings.

Erosion by water

Temperature changes cause pieces of rock to flake away from the surface. Also, the acid in rainwater dissolves rocks containing calcium carbonate. These processes are called weathering.

Water erosion happens when water moves the pieces of rock or soil downhill. Waves also carry away small pieces of material. A wave can wash up onto the surface of rock or soil and then carry away pieces of material as it flows back into the ocean or lake.

The size of earth materials that can be moved by water depends on how fast the water is moving. A fast-flowing stream can carry large rocks while a slow moving stream might only be able to carry very small things like clay. Canyons, like the Grand Canyon, are among the most obvious features made by erosion. Where a river meets the sea, it drops the solids, sometimes making a river delta.

Tropical rivers

Large tropical rivers like the Paraná, Indus, Brahmaputra, Ganges, Zambezi, Mississippi and the Amazon carry huge amounts of sediment down to the sea. The Nile, perhaps the world's longest river, carries much less sediment than the others because, part of the way, it runs through less fertile regions than the other great rivers.

The Amazon has by far the largest waterflow, with an average discharge greater than the next seven largest rivers combined. It has the largest drainage basin in the world, about 7,050,000 square kilometres (2,720,000 sq mi). The Amazon accounts for about one-fifth of the world's total river flow.

The sediment discharged by the gigantic mouth of the Amazon stains the sea brown for hundreds of miles out to sea.

Erosion by ice

Ice erosion happens when a glacier moves downhill. As the ice of the glacier moves downhill, it pushes and pulls earth materials along with it. Glaciers can move very large rocks. Ice erosion can happen in another way. Cold weather causes water inside tiny cracks in rocks to freeze. As it freezes, the ice gets bigger, and pushes hard against the rock. This can break the rock.

Erosion by wind

Wind erosion occurs when wind moves pieces of earth materials. Wind erosion is one of the weakest kinds of erosion. Small pieces of earth material can be rolled along the ground surface by wind. Very small pieces can be picked up and carried by the wind. Sometimes, wind can carry small pieces of earth materials over large distances. Some sediment from the Sahara Desert is carried across the Atlantic Ocean by wind.

One of the most famous examples of wind erosion occurred in the Dust Bowl, when wind erosion severely damaged farming communities.

Erosion by gravity

Gravity erosion is the simplest kind of erosion. Gravity simply pulls loose earth materials downhill. Landslides are dramatic examples of gravity erosion.

Erosion and tectonics

Tectonic effects on erosion has long been recognized. For example, rivers form as a result of tectonic uplift (as Himalayas and Tibetan Plateau). All of the Earth's mountain ranges were created by the upward movement of the land by changes beneath the Earth's surface. When the ground rises the whole weather system can also be changed including local sea levels, wind strength and direction, rainfall and more.

The Earth's landscape is a product of two factors. Tectonics builds up height by surface and rock uplift, and climate controls the erosion. Erosion wears away upland areas over time. The interaction of these processes can form, modify, or destroy features of the Earth's surface.

Images for kids

Wave cut platform caused by erosion of cliffs by the sea, at Southerndown in South Wales

In Spanish: Erosión para niños

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Ever heard the word erosion in Geography or someone talking about it, and you don't know what it is? Well read on, and we'll tell you all you need to know. What is erosion? Erosion is where land is worn away by different forces. These forces can be water, wind and ice.

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Kids learn about the Earth science subject of erosion including water, wind, and glacial erosion, fun facts, human causes, and controlling it.