Weathering

What is weathering?

The process that breaks down rock into smaller

pieces, called sediments.

Not to be confused with WEATHER!

There are two types of weathering:

Rocks are physically broken into smaller

pieces.

Rocks are broken down through chemical

changes.

The rate of weathering is affected by climate.

Mechanical happens faster in the cold weather.Chemical is faster in warm weather.

Mechanical Weathering

(physical)

Chemical Weathering

Forms of Mechanical Weathering

Ice Wedging

Exfoliation

Abrasion

Plants and animals

Ice Wedging (a.k.a. Frost wedging)

The cycle of water freezing and thawing in the cracks of rocks, causing the rock to break.

Click the picture for ice wedging animation!

ExfoliationPressure causes rocks to crack and “peel’ away in slabs.

Abrasion

Sediments carried by wind or water rub against other rock and wear it down. Like sandpaper!

Plant Wedging

Plant roots grow large and break apart rock.

Animals

Animals burrow into the ground and loosen sediment and soil.

Surface Area of Rock

As rock is broken apart by mechanical

weathering, the amount of rock

surface area exposed to air and water increases.

These smaller pieces will be

weathered faster than a larger piece.

EXIT SLIP1. What is weathering?

2. How do mechanical weathering and chemical weathering differ?

3. What type of weather conditions would increase the rate of chemical weathering?

4. The diagram shows the process of ice wedging. Explain how this process physically weathers rocks.

5. How can plants and animals contribute to the mechanical weathering process?

Forms of Chemical Weathering

Oxidation

Dissolution

Hydrolysis

Organic Acids

OxidationWhen materials that

contain iron are exposed to oxygen and water, they become a reddish color.

Ayer’s Rock, Australia

Dissolution Carbonic acid in rain dissolves rock. This can form caves and cause sinkholes.

Hydrolysis

Water combines with the minerals in rock and cause a chemical change.

If water combines with the mineral feldspar, clay is formed.

Organic Acids

Plant roots give off acids that dissolve rock.

EXIT SLIP6. Oxidation occurs when materials that contain iron are

exposed to what two compounds?

7. Dissolution can form sinkholes. Explain the process of dissolution.

8. How do plants and animals chemically weather rocks?

Can you tell which mountain is older?

What is soil?

A mixture of weathered rock, decayed organic matters, mineral fragments, water, and air.

Factors Affecting Soil Formation