AIM: What causes weathering and

erosion?

Weathering is the physical and chemical breakdown of rocks into smaller pieces called sediment.

Due to:• Air• Water• Pressure changes• Actions of living things

Physical Weathering• Breaking a rock by force– Ex: hitting, scratching, cracking

• The smaller pieces of rock have the same composition as the rock they came from.

• CAUSES OF PHYSICAL WEATHERING:1. Freezing & Thawing (ice wedging): a) Water seeps into cracks in rocks and freezes

when the temperature drops.b) Water expands when it freezes.c) With repeated freezing and thawing, the cracks

expand until pieces of the rock break off.

Ice Wedging• Happens the most in areas where

the temperature swings above and below freezing

2. Release of Pressure (exfoliation): a release of pressure can cause outside layers of a rock to crack and flake off like an onion

3. Plant Growth: roots of plants can enter tiny cracks in rock and force the cracks further apart.

4. Abrasion• This process occurs when sediments carried by

streams and wind blown sand causes particles to collide into each other and the surrounding rock.

Chemical Weathering• Rock material is changed into

another substance by reacting with a chemical.

Causes of Chemical Weathering1. Water: weathers rock by DISSOLVING it. - most important cause of chemical weathering

Weathering Granite

Causes of Chemical Weathering2. Oxygen: oxygen in the air can combine

with minerals in a rock.– For example, when oxygen combines with iron

minerals, iron oxide (RUST) forms. – The chemical change of the mineral weakens the

rock and the rock crumbles.

Causes of Chemical Weathering3. Carbon Dioxide: dissolves in rainwater to

form carbonic acid.- Carbonic acid reacts with certain rocks and minerals that include: calcite, limestone, marble and chalk.

Caves form as a result of carbonic

acid weathering

rock

Sinkholes formed as a result of chemical weathering

Limestone bedrock

Carbonic acid rain water seeps into the limestone bedrock through the cracks. This water dissolves the limestone rock.

1. Sinkholes2. Columns3. Stalactites4. Stalagmites

Causes of Chemical Weathering4. Living Organisms: plants can produce acids that chemically breakdown rock.

Lichens chemically weathering a fallen tree

5. Man-made Acids – Gases produced by humans can dissolve in the water droplets of a cloud to produce acid rain.– H2SO4 – sulfuric acid– HNO3 – nitric acid

Causes of Chemical Weathering

Acid Rain formation

What affects the RATE of weathering?

1. Type of Rock: some minerals break down more easily than others.

What affects the RATE of weathering?

2. Climate: weathering occurs FASTER in locations with wet climates.

Due to climate and different weathering processes, landscapes

develop differently.

Arid climate Humid climate

What affects the RATE of weathering?

3. Particle Size: Weathering takes place on the outside surface of rocks. –The more surface area that is exposed to

weathering, the faster the rock will be broken down. –As a rock breaks into smaller pieces, the surface

area increases, therefore the rate of weathering increases.

A full solid block has the least surface area. The interior is safe from exposure.

A smashed piece has the greatest surface area exposed. The interior can now be attacked.