Weathering and Erosion

Natures way of tearing down everything that has been built up

over billions of years.

What is mechanical weathering?

Objective- explain the ways that Earth’s surface is worn away by mechanical weathering.

Weathering- breaking down of rocks and other materials on Earth’s surface.

Mechanical weathering- weathering in which the chemical makeup of rocks does not change.

* Involves only physical changes, such as size and shape.

Mechanical weathering occurs as a result of;– temperature changes.– Ice wedging– Root action

Mechanical Weathering

Temperature Changes• Rocks may be broken apart by temperature changes.

– Heat makes them expand. (daytime)– Cooling makes them contract. (night time)Exfoliation- the peeling of rock layers, created by temperature

extremes. (creates domed rocks)Ice wedging- mechanical weathering caused by the freezing and

melting of water.When water freezes it expands by 10%.Water enters cracks in the rock freezes, expands and

widens the crack. Repeated actions cause rocks to split apart.*Root wedging- Plant root in search of minerals and water can

grow in cracks of rocks.Roots force rocks apart, breaking them into smaller

pieces.*Burrowing animals- animals that dig next to rocks, exposing

them to the elements of weather.

Mechanical Weathering

Exfoliation

Mechanical Weathering

Ice wedging (frost wedging)

Mechanical Weathering

Root Wedging

Mechanical Weathering

Burrowing Animals

What is chemical weathering?

Objective- Explain how Earth’s surface is worn away by chemical weathering.

Types of Chemical weathering;

In chemical weathering, substances in water cause substances in rock to dissolve.

*Chemical changes in rock occurs when minerals are broken down into new substances.

*Chemical weathering is usually caused by reactions with; oxygen, water, or acids.

Chemical Weathering

Oxidation- chemical change that occurs when oxygen reacts with another substance.

New substances called oxides form.

*Rocks containing ferromagnetic minerals combine with oxygen forming rust. The rock is weakened and crumbles as a result of this process.

2Fe2SiO4 + 2H2O + O2 = 2Fe2O3.H2O + SiO2

Chemical Weathering

Hydration- chemical reaction that occurs when minerals with little water content react with water.

*Most chemical weathering is caused by water. When feldspar reacts with water it turns to clay.

Na-feldspar and K-feldspar undergo hydrolysis to form kaolinite (clay) and Na+ and K+ ions.

Chemical Weathering

Carbonation- chemical reaction that occurs when carbonic acid reacts with certain minerals.

*Carbon dioxide can dissolve in rain to form carbonic acid.

When the carbonic acid comes into contact with certain minerals a chemical reaction occurs called carbonation. The mineral calcite reacts with carbonic acid.

Chemical Weathering

Carbonation

Chemical Weathering

Acids and weathering

*Plants produce weak acids which can react with minerals weakening a rock and dissolve those minerals.

Factors that affect the rate of weathering.

Objective- Identify three factors that affect the rate of weathering.

#1 Climate

* moisture speeds up chemical weathering.

* weathering occurs fastest in hot, wet climates.• In very cold, dry areas, there is little weathering.

#2 Surface area

* Weathering occurs on exposed surface areas of rocks and minerals.

* The more surface area a rock has, the faster it will weather.

Factors that affect weathering

#3 Rock composition

* Slow weathering minerals; Quartz

* Fast weathering minerals; feldspar

* Weathering by carbonation; Calcium (limestone)

* Weathering by Oxidation; Iron

Factors that affect rate of weathering

#4 Chemical reactions

* Carbonic acid weathers calcite (limestone/marble)

• Natural weathering through carbonation is slow.

• Anthropomorphic (human activity); factories produce carbon dioxide, sulfur and nitrogen. When combined with rainwater they produce acids or acid rain.

• Acid rain- rain containing acids produced by water chemically combining with certain gases.

How does soil form?

Objective- explain how soil is a product of weathering and organic processes.

Formation of soil

Bedrock- solid rock that lies beneath the soil.• Bedrock is the parent material of soil. Weathering breaks

bedrock into soil.

Soil formation

Living things and soil

Humus- decaying remains of plants and animals.

* Water helps speed up the breakdown of rock.

Soil formation

Soil- mixture that includes silt, sand and clay.• Weathered pieces of rocks, minerals and humus are also

in soil.• Soil that is rich in humus is very dark.

Importance of soil

* Soil is important to plants. Potassium, phosphorous and nitrogen are important nutrinets.