Weathering and Soil Formation Ch 10 Mrs Hutson

Weathering and Soil Formation Ch. 10 * Mrs. Hutson

What is weathering? n Weathering is the process by which rocks are broken down. – This can be either: § Mechanical § Chemical

Mechanical a. k. a. Physical n Mechanical weathering is the breakdown of rock into smaller pieces by a physical means. For example: – Wind – Water – Animals – Plants – Ice – Gravity

Think about it! n Which of the following things cannot cause mechanical weathering? – A. – B. – C. – D. Water Acid Wind Animals

Ice Wedging n Water seeps into cracks in rock. Then when it freezes it expands. This causes the cracks to enlarge.

Ice/Frost WEDGING

Pot Holes: a common form of ice wedging

Abrasion n The weathering or rocks due to them rubbing against other rocks or particles.

Wind, Water, Gravity n These are all ways that abrasion occurs.

Formed by wind abrasion Valley of Fire State Park (Nevada)

ABRASION OF WIND AND WATER

Formed by wind abrasion Arches Nation Park (Utah)

Think about it! n What are three ways abrasion occurs in nature?

Think about it! n What are three ways abrasion occurs in nature? Answer: Wind, Water, & Gravity

n Some plants can easily break through rocks. Plants

Plant Activity: Roots Split Rock

Animals n Burrowing animals such as rats, earthworms, ants, coyotes, and rabbits cause a lot of weathering.

Which method of mechanical weathering is shown below? ____________

Which method of mechanical weathering is shown below? ____________

Which method of mechanical weathering is shown below? ____________

Which method of mechanical weathering is shown below? ____________

Chemical Weathering n Chemical weathering is the process by which a rock is broken down as a result of a chemical reaction.

Water n Water is the main ingredient in chemical weathering. n It may take thousands of years, but water can even break down granite.

Acid Precipitation n Acid precipitation is any rain, sleet, or snow that contains large amounts of acid. n All precipitation is naturally acidic, however, acid precipitation contains more than normal.

Acid can also be found in groundwater or in the air. n Oxidation is the chemical reaction that occurs when elements react with oxygen.

Think about it! n Why does acid precipitation weather rocks faster than normal precipitation?

Think about it! n Why does acid precipitation weather rocks faster than normal precipitation? – Answer: Acid precipitation is more acidic than natural precipitation. Stronger acids break down rocks faster.

Summary Questions n 1. Explain the difference between mechanical and chemical weathering.

Answers Q: Explain the difference between mechanical and chemical weathering. A: Mechanical weathering is the breaking down of rock into smaller pieces by physical means only and chemical weathering is the process of breaking down rocks as a result of a chemical reaction.

Summary Questions 1. Describe how humans contribute to the process of chemical weathering.

Answers Q: Describe how humans contribute to the process of chemical weathering. A: Humans produce man-made gasses by burning so much fossil fuel (coal, oil, natural gas). These gases react with water and produce acid rain. This acid rain literally “eats” away at rocks.

Rates of Weathering n Ch. 10 Section 2

Rates of Weathering n Hard rocks weather slower than soft rocks. n This is also called differential weathering.

Devils Tower in Wyoming

Devils Tower in Wyoming

What Happened? n Long ago, magma cooled in the center of a volcano to form igneous rock. n Over time, the outer rock, softer rock weathered away leaving only the harder inner rock.

Think about it! n. A rock will have a lower rate of weathering when the rock – A. Is in a humid climate. – B. Is a very hard rock, such as granite. – C. Is at a high elevation. – D. Has more surface area exposed to weathering.

Surface Area n Because weathering occurs on the surface of rocks, the more surface area exposed to weather the faster a rock will weather.

Climate affects weathering. n Climate area. is average weather condition in an

Warm, humid climate n Chemical weathering occurs faster in warmer, wetter climates. n Like Georgia

Water and Temperature n More water and lower temperatures affect mechanical weathering. n If water freezes and thaws often then ice wedging occurs more.

Mountain Tops n Mountain tops weather faster because they are exposed to more wind, rain, and ice.

Think about it! n Why does the peak of a mountain weather faster than the rocks at the bottom of the mountain?

Think about it! n Why does the peak of a mountain weather faster than the rocks at the bottom of the mountain? – Answer: Rocks at the peak of a mountain weather faster because they are exposed to more wind, rain, and ice.