Weathering and Soil Formation

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

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

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

Ice Wedging 2. The water freezes (ice expands). This causes the cracks to get larger. 3. The cracks get so large that the rock breaks apart. 1. Water seeps into cracks in rocks.

Abrasion The weathering of rocks due to them rubbing against other rocks or particals.

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

Plants Some plants can easily break through rocks.

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

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

Water Water is the main ingredient in chemical weathering. It may take thousands of years, but water can even break down granite. See the difference? 1908 1968

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

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

Weathering Review Give three ways that living organisms can weather rocks. How does ice wedging occur? Give an example of how water can weather rocks mechanically (physically). Give an example of how water can weather rocks chemically. How does gravity help weather rocks?

Rates of Weathering

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

Devils Tower in Wyoming

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

Devils Tower

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

Warm Up Explain how climate affects the rate of chemical weathering. 2. Explain how climate affects the rate of mechanical weathering. 3. Describe how parent rock is used in the formation of soil.

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

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

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

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

From Bedrock to Soil

What is soil? Soil is a loose mixture of small mineral fragments, organic material, water, and air that can support the growth of vegetation.

All soil is different Soil (weathered rock fragments) can be made of many different types of rock. The type of rock that the soil was made from is called parent rock.

Parts of Soil

Bedrock Bedrock is the layer of rock beneath the soil. Some soil is made from bedrock, so it remains above the parent rock.

Humus Humus is the dark, organic material in soil that is formed from decayed remains of plants and animals.

Soil Horizons Soil is usually layered with humus-rich soil on top, sediment below that, and bedrock on bottom.

Soil Conservation

Soil Conservation Soil Conservation is a method to maintain the fertility of soil by preventing erosion and the loss of nutrients.

Importance of soil Soil provides nutrients to plant life. If the soil losses these nutrients then the plants will not grow. All animals get energy from plants. How can unhealthy soil effect us?

Housing and Water Soil is also important to providing shelter for animals that live in soil. It also stores water for plants and animals, and helps prevent flooding.

Can you tell which is grown in healthy soil?

Land Degradation When soil is overused it loses its nutrients. This can happen from poor farming techniques or overgrazing. Plants can’t grow in infertile soil. Without plants and moisture the soil can be washed or blown away.

Erosion Erosion is the process by which wind, water, or gravity transport soil and sediment from one location to another. This happens when land is left unprotected. This happened in south Georgia long ago. The result was Providence Canyon. What was once cotton fields is now a 150 ft. deep canyon.

Providence Canyon

Providence Canyon

Providence Canyon

Providence Canyon

Providence Canyon

Soil Conservation There are many ways that farmers help prevent erosion. Contour plowing Terracing No-till farming Cover crops Crop rotation

Contour Plowing

Terracing

No-till farming

Cover crops Cover crops are crops such as soy beans and peanuts that help restore important nutrients to the soil.

Crop rotation Rotating crops from one year to the next.