Prentice Hall EARTH SCIENCEEARTH SCIENCE

Tarbuck Lutgens

Chapter

55 Erosion and weathering are major forces

that shape Earth’s surface.

For example, the Grand Canyon was formed through erosion by the Colorado River running through it!

Weathering, Soil, and Mass Movements

Mechanical Weathering

5.1 Weathering

Mechanical weathering occurs when physical forces break rock into smaller and smaller pieces without changing the rock’s mineral composition.

In nature three physical process are especially important causes of weathering: frost wedging, unloading, and biological activity.

What is weathering?

Weathering: The breaking down of rocks into smaller pieces.

1. Mechanical /Physical

2. Chemical

So what is erosion?

Erosion:

The movement

of weathered

rock by wind, water, glaciers & gravity

5 Agents of Mechanical Weathering:

1. Release of Pressure

2. Freezing & Thawing

3. Animal Actions

4. Plant Growth

5. Abrasion

Mechanical Weathering

5.1 Weathering

• Reduced pressure on igneous rock causes it to expand and allows slabs of outer rock to break off in layers in a process called exfoliation.

1. Release of Pressure

Unloading and Exfoliation of Igneous Rocks

Mechanical Weathering

5.1 Weathering

2. Frost wedging

• The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices

Freezing & ThawingWhen water in the cracks

of rocks freezes it expands causing the crack to enlarge or get bigger. The ice melts & refreezes over & over, breaking the rock apart.

Frost Wedging

Mechanical Weathering

5.1 Weathering

3. Biological activity

• The activity of organisms, including plants, burrowing animals, and humans, can also cause mechanical weathering.

Mechanical Weathering

5.1 Weathering

3. Biological - Plant growth

• Plants roots can grow into cracks in the rock, slowly breaking them apart.

Plant Root Growth

Weathering and Biological Activity

Mechanical Weathering

5.1 Weathering

4. Biological – Animal actions

Animals dig (burrow) through the ground to make their homes. This loosens the soil & breaks apart rocks.

5.1 Weathering

5. Abrasion

Sand and other rock particles in wind, water or ice can wear away exposed rock surfaces.

Like sandblasting or sandpaper on wood

Sand-Blasting

Chemical Weathering

5.1 Weathering

Chemical weathering is the breaking down of rock through chemical reactions.

Chemical Weathering

5.1 Weathering

5 Agents of Chemical Weathering1. Water2. Oxygen3. Carbon Dioxide4. Living Organisms5. Acid Rain

Chemical Weathering

5.1 Weathering

5 Agents of Chemical Weathering1. Water – Water dissolves rock.

Chemical Weathering

5.1 Weathering

5 Agents of Chemical Weathering1. Water – Water dissolves rock.2. Oxygen – Chemically changes rock

through a process called Oxidation.

Oxygen + Water + Iron = RustOxygen + Water + Iron = Rust

Rusted rock on hillsideRusted rock on hillside

Chemical Weathering

5.1 Weathering

5 Agents of Chemical Weathering1. Water – Water dissolves rock.2. Oxygen – Chemically changes rock

through a process called Oxidation.3. Carbon Dioxide – forms carbonic acid.

Chemical Weathering

5.1 Weathering

CO2 + rainwater = Carbonic Acid

Carbonic Acid weathers softer rock like limestone & marble as it seeps into spaces in rock.

Examples: Karst topography – caves, sinkholes

Chemical Weathering

5.1 Weathering

Examples: Karst topography – caves, sinkholes

Chemical Weathering

5.1 Weathering

5 Agents of Chemical Weathering1. Water – Water dissolves rock.2. Oxygen – Chemically changes rock

through a process called Oxidation.3. Carbon Dioxide – forms carbonic acid.4. Living Organisms -

The roots of plants make a weak acid that slowly dissolves rocks around the plant.

Chemical Weathering

5.1 Weathering

5 Agents of Chemical Weathering1. Water – Water dissolves rock.2. Oxygen – Chemically changes rock

through a process called Oxidation.3. Carbon Dioxide – forms carbonic acid.4. Living Organisms -

Chemical Weathering

5.1 Weathering

5 Agents of Chemical Weathering1. Water – Water dissolves rock.2. Oxygen – Chemically changes rock

through a process called Oxidation.3. Carbon Dioxide – forms carbonic acid.4. Living Organisms - Lichen, mosses5. Acid Rain – rapid weathering

5.1 How does Acid Rain form?

Acid rain dissolves granite

Acid rain dissolves limestone and marble

Click

• http://classroom.synonym.com/effects-acid-rain-cemetery-stones-19291.html

• http://www.dnrec.state.de.us/DNREC2000/Divisions/AWM/aqm/education/airqualityLesson6.pdf

• Summary & Quiz

Rate of Weathering

5.1 Weathering

Increased surface area = Increased weathering