Weathering and Erosion

by Tom Day


What weathering is.

Weathering is a process in which rocks are worn away.

Mechanical Weathering

What mechanical weathering is.

Mechanical weathering is the process in which rocks are broken down through a physical change. The three main types of mechanical weathering are by temperature, by wind, rain and other water and by ice.

Weathering by temperature.

When rocks get hotter they expand. When they cool they contract. If a rock expands and contracts a lot it forms cracks and the outside breaks off.

Weathering by wind, rain and water.

Rain and water carry debris that can cut into rock. Wind blows small particles that scrape against rocks. When a rock bumps into another rock the force can cause breaks in the rock to form or break off a piece of rock. Wind can blow small particles that scratch other rocks and slowly weather them.

Weathering by ice.

Water expands when it freezes so when it is ice it takes up more space than when it is water. Water can freeze in a crack in a rock. When water freezes in a crack in a rock it expands pushing the crack further apart. When it thaws the crack in the rock stays. Then new water can come in and freeze. Then the water freezes and pushes the crack even further apart. Eventually the crack gets so big that part of the rock falls off.
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This picture is an example of physical weathering because it shows a river cutting into a canyon.

Chemical Weathering

Definition of chemical weathering.

Wearing away of rocks by chemicals.


Hydrolysis is the process in which water is broken into H and HO molecules. These molecules can react with other rocks.

Rain and Acid Rain.

Rain and Acid Rain are acidic but normal rain is only a little acidic. The acid in the rain can cause chemical reactions. One example is Calcite (CaCO3) which fizzes and leaves a material that is easily moved away.
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This picture is an example of chemical weathering because it shows damage to a stone work by acid rain.

Biological Weathering

What biological weathering is.

Biological weathering is when plants and or animals ware away rocks. The two main types of biological weathering is plant roots and animals.

Weathering by plant roots.

Plant roots can enter cracks in rocks. As the roots grow they start to push at the rock. The crack then gets bigger. Eventually the crack gets big enough that part of the rock breaks off.

Weathering by animals.

Animals can ware away rocks over time. Paths are worn down by feet and hooves over time. Humans mine which weathers rocks.
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This picture is an example of biological weathering because a human is breaking rocks.


Definition of erosion.

The moving of rocks from one place to another.

Erosion by Wind

How it happens.

Wind blows small particles over time they can travel large distances.

What rock sizes are carried.

Small particles like ash, sand and dust are moved because they are relatively light.

Effects on Landforms

This makes Sand dunes and can move a mountain over time. It also makes Arches like in Arches national park and can cause sandstorms.
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This picture is an example of wind erosion because it shows sand being blown by the wind.

Erosion by Water


Water flowing downhill can push rocks along with it. And some substances dissolve in water and are carried away with the water.

What rocks can be carried?

The faster the stream the larger the rock can be carried. Slow stream may only be able to move silt and sand. Fast rivers may move boulders.

What happens to Land forms.

Water can carry away or drop sediments in areas and change the shape of the coastline. Water can carve canyons one example is the grand canyon. Flooding can even move cars and houses.
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This picture is an example of water erosion because it shows a river carrying sediments.

Erosion by Gravity


Gravity a force pulling down on all things can pull a rock downhill or just straight down. When water undercuts rock gravity eventually pulls it down.

How big of a rock can gravity move

All of the rocks on earth are effected by gravity. This means that any rock can be pulled down by gravity. Even the moon is effected by gravity which isn't on the earth.

Effects on land forms.

The pulling of gravity can make sinkholes. This happens when the ground can't support the dirt above it and it falls down. Gravity also makes valleys, lakes, plains and change coastline
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This picture is an example of gravity erosion because it shows rocks that were dragged down from above.

Erosion by Glaciers

How it happens.

Glaciers slowly move downhill and and pick up or push almost everything they come across. The items they pick up gouge the land around them also.

Rock sizes.

They pick up whatever they find that's loose. Anything from sand to boulders could be picked up.

Effects on land forms.

They make valleys, lakes, basins, rivers and kettles.
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This picture is an example of glacial erosion because it shows a glacier moving small rocks

Cited Sorces


National Geographic

Eschool today

Discovery Education

Britanica Image Quest