Weathering

Weathering

What is weathering?

Weathering is the breakdown and alteration of rocks and minerals near or at the Earth’s surface.

The two types of weathering are: 1. physical or mechanical weathering 2. chemical weathering

Physical Weathering

• the breaking of rocks into smaller fragments without changing their mineral or chemical composition

• joints are cracks in rocks formed by tectonic forces

Physical Weathering

1. frost action – rocks break as water freezes in cracks Click for

animation!

Physical Weathering

2. abrasion or impact weathering – rocks break down when exposed to agents of erosion

Physical Weathering

2. abrasion or impact weathering – rocks break down when exposed to agents of erosion

Physical Weathering

3. pressure release – rocks fracture as they expand when exposed from beneath the Earth’s surface

Physical Weathering

4. insolation weathering – rocks break due to exposure of extremes of temperatures resulting in repeated expansions and contractions

Click for animation!

exfoliation – outer layers of rock peel off following pressure release or insolation weathering

Physical Weathering

5. biological weatheringa. rocks break as plant roots grow in cracksb. rocks and minerals break down as animals burrow and move Click for

animation!

Chemical Weathering

• the minerals or chemicals in rocks are altered and new substances are formed

• water is needed for chemical reactions to take place

Chemical Weathering

1. leaching – water dissolves chemicals in rocks and washes them away

iron leaching

Chemical Weathering

2. hydration - certain minerals absorb water and produce new substances (ex. feldspar + water → kaolinite, a type of clay used in pottery)

Click for animation!

Chemical Weathering

3. oxidation – certain minerals combine with oxygen in air or water forming oxides (ex. iron + oxygen → rust)

Click for animation!

Chemical Weathering

4. carbonation weathering – rocks with calcite (ex. limestone) are dissolved away by carbonic acid produced from water combining with CO2

Chemical Weathering

5. acid rain – sulfur and nitrogen oxide air pollutants combine with rain droplets forming acids that break down rocks

Chemical Weathering

6. biological weatheringa. chelation – organisms such as lichens and moss produce acids that break down rocks

Chemical Weathering

6. biological weatheringb. organisms can influence environmental factors that may enhance weathering (ex. moisture and pH)

Rate of Weathering

1. The bigger and more numerous the joints in a rock, the faster is the rate of weathering.

2. Climate affects the rate of weathering. a. Frost action depends on rain, snowfall and

temperature ranges. b. Chemical weathering is enhanced in humid

climates.

Rate of Weathering

3. The mineral composition of a rock may make it more or less susceptible to weathering.a. Quartz is resistant to both physical and chemical weathering.b. Calcite is easily dissolved away by carbonic acid.

Products of Weathering1. rock fragments2. rock formations3. limestone caves4. soil5. sediment6. nutritional minerals for plants7. solutes in bodies of water

Exercise

Physical or chemical?

Vocabulary matching

• abrasion• chelation• exfoliation• oxidation

Vocabulary matching

• abrasion• chelation• exfoliatio

n• oxidation

Vocabulary matching

• abrasion• chelation• exfoliation• oxidation

Vocabulary matching

• abrasion• chelation• exfoliation• oxidation

Reflection:Watch the following slideshow in silence. Look

at each picture. Be sensitive to the feelings and ideas each one evokes.

Choose the picture that made the most impact on you. Describe it. How did it make you feel? What thoughts and ideas came to you? Write a short reflection (5 to 10 sentences) about it.

The End