Weathering and Erosion

By: Betsy and Brittany


Definition~ Weathering is the continuous breakdown of rocks.

Mechanical/Physical Weathering

Definition~ Physical weathering is the breakdown of rocks when temperature, weather (rain, wind), or physical changes occurs.

How does it occur (Examples)~

> Temperature: When rocks are cooled, the rocks contract; and when rocks are warmed, they expand. When the process of contracting and expanding happens too much, this is when rocks crack.

> Wind, waves, and rain: This happens when rain and waves breakdown grains of rock by raining on rocks and waves colliding with rocks. Over time this will cause the rock to break away. Wind will pick up and sweep away rocks and even push rocks and push against cliffs.

> Freeze and Thaw: When water get through to a crack in a rock and then is frozen , it expands the rock/ crack. When the water thaws it then get further into the crack and expands it even more until the rock breaks.

Chemical Weathering

Definition- Chemical weathering is the breakdown of rocks when chemicals are involved.

How does it occur (Examples)~

>Acid Rain: The chemical is formed when fossil fuels are burned. Carbon dioxide and sulfur outbreak from the fossil fuels and diffuse into the air, leaving the chemicals to dissolve in the clouds with the water. The rainwater is then toxic which the the water on the rocks are more dangerous and cuts through the rocks.

> Hydrolysis: When water breaks apart to H+ and OH, the elements then react causing their atom in compositions to be destroyed.

Biological Weathreing

Definition- Biological weathering is when plants, animals or any living thing breaks down rocks.

How does it occur (Examples)~

>Animals: An animal can breakdown a rock by crawling into a crack of the rock and widening the crack until it splits or just gets bigger.

>Plants: A rock could be sitting on top of a plant root and the plant can grow through the rock or pavement and split the rock open.


Definition- Erosion moves rocks and sediments.

Erosion by Wind

How does it occur?:

When wind blows it picks up sediments and moves them to different areas. Also when rocks are moved they can hit other rocks and cause erosion as well.

Sediment sizes that are carried:

Dust, sand, and volcanic ashes can be carried by wind and this happens when the sediments break off from the rock and wind sweeps it up and carries it around.


>Sand dunes can be made by wind and sand

>Wind blasts against cliffs and make it smoother

>Creates arches

>Creates Dust storms

>Dries out lands

Erosion by Water

How does it occur?:

When water flows it picks up rocks big and small and slowly chips away rock fragments.

Sediment sizes that are carried:

All different size sediments can be carried by water. Boulders can be carried in a flood to just a little particle of sand getting washed away on a beach.


> Creates Rivers like the Fox River

> Boulders rushing in water during a flood

> Creates Canyon like the Grand Canyon

> Creats Creeks like Antietam Creek in Maryland

> Disappearance of beaches

> Expands coastlines and beaches

Erosion by Gravity

How does it occur?:

Gravity can cause erosion by bringing/ pulling rocks and boulders down a mountain. When the rock comes down, it hits other rocks forcing the rock (part of the mountain or hill) to break or take sediments away from the mountain.

Sediment sizes that are carried:

Any size rock, as long as it starts to fail/ break off because gravity pulls everything down, big or small.


> Brings Avalanches down

> Brings Flowing water down

> Creates Landslides

> Creates Sinkholes

Erosion by Glacier/Ice

How does it occur?:

A glacier occurs when snow doesn't melt or water freezes into very thick blocks of ice. These blocks are normally massive The weight is what moves it along its path along with gravity. When moving the glacier scrapes against landforms and scoops up sediments that can get frozen to the glacier.

Sediments that can be carried:

Glaciers can pick up any size sediments. The can scoop/scrape up sand from a beach. Also glaciers can scoop up boulders that eventually freeze to the side of the glacier.


> Glaciers can carve canyons

> Glaciers can melt into lakes. (Lake Michigan)

> Glaciers can scrape over the land and destroy it moving sediments away from their original spots.

> Creates Valleys

> Creates Plains

> Creates Glacier lakes

> Creates Coastlines


National Geographic

KS3 bitesize