7-1 Rocks and Weathering

WEATHERING AND SOIL

FORMATIONChapter 7

ROCKS AND WEATHERING

Chapter 7 Section 1

EFFECTS OF WEATHERING

Weathering is the process that breaks down rock and other substances at Earth’s surface

Heat, cold, water, and ice all contribute to weathering

Oxygen and Carbon Dioxide also contribute

Forces of weathering break rocks into smaller and smaller pieces

Erosion is the movement of rock particles by wind, water, ice, or gravity

WHAT IS THE DIFFERENCE BETWEEN WEATHERING AND EROSION?

Weathering is the process the process that breaks down rock and other materials at Earth’s surface, while erosion is the movement of rock particles by wind, water, ice, or gravity

MECHANICAL WEATHERING

Mechanical Weathering- type of weathering in which rock is physically broken into smaller pieces

Mechanical weathering breaks rock into pieces by freezing and thawing, release of pressure, growth of plants, actions of animals, and abrasion

Abrasion- the grinding away of rock by rock particles carried by water, ice, wind, or gravity

Mechanical weathering works slowly over time and can wear away whole mountains

Ice wedging- frozen wedges of ice in rocks widen and deepen cracks

CHEMICAL WEATHERING

Chemical weathering- process that breaks down rock through chemical changes

Agents of chemical weathering include water, oxygen, carbon dioxide, living organisms, and acid rain

Chemical weathering creates holes or soft spots in rock, and rocks break apart more easily

Water

Water is the most important agent of chemical weathering

Water dissolves rocks

Oxygen

Oxygen in the air combines with iron causing oxidation

Carbon Dioxide

Living Organisms

CO2 dissolves in rainwater and forms carbonic acid

Carbonic acid easily weathers marble and limestone

Roots of organisms push into cracks in rocks

Plants roots produce weak acids that slowly dissolve rock

Lichens- plant like organisms that grow on rocks- also produce weak acids

Water is the most important agent of chemical weathering

Water dissolves rocks

Acid Rain

LICHEN

RATE OF WEATHERINGType of Rock

The minerals that make up the rock determine how fast it weathers

Rocks that dissolve easily in water weather more quickly

Permeable- a material is fully of tiny, connected air spaces that allow water to seep through it

Permeable rock weathers at a fast rate

Climate Climate- the average

weather conditions in an area

Chemical and mechanical weathering occur faster in wet climates

Rainfall provides the water needed for chemical changes as well as for freezing and thawing

Chemical reactions occur faster at higher temperatures

REVIEW 1. What factors cause mechanical weathering?

Freezing and thawing, heating and cooling, growth of plants, actions of animals, and abrasion

2. Describe three causes of chemical weathering.

Water that dissolves rocks, oxygen causes oxidation, carbon dioxide dissolves in rainwater, living organisms, and acid rain

3. What factors affect the rate of weathering?

Type of rock and climate

4. Explain why chemical weathering occurs faster in hot, wet climates than in cool, dry climates.

Rainfall provides the water needed for chemical changes and higher temps cause chemical reactions to occur faster