Weathering and Erosion

1. Weathering and Erosion By 6C

2. The Appalachian Mountains appear very different from the Sierra Mountains. The Appalachians are smaller, rounded, gently sloping, and covered with plants. The Sierras are twice as high, and very rocky and steep. Old and New Mountains

3. The process that breaks down exposed rock and turns it into soil. Heat, cold, water, and ice all can weather rock. Rocks get weathered into smaller and smaller pieces, forming the basis of soil. Weathering

4. Mechanical weathering is when rock is physically broken into smaller pieces It breaks rock down into pieces by freezing and thawing, releasing pressure, growth of plants, actions of animals, and abrasion. Mechanical Weathering

5. Abrasion is the grinding away of rock by particles carried by wind, water, ice, or gravity. Nature’s way of sandblasting. Works slowly, but over millions of years can wear down mountains. Abrasion

6. Ice Wedging • When the ice melts, the water seeps deeper into cracks. With repeated freezing and thawing, the cracks slowly expand until pieces of rock break off.

7. Chemical weathering is the process that breaks down rock through chemical changes. The agents of chemical weathering include Water Oxygen Carbon dioxide Living organisms Acid rain Key idea: new substances are made! Chemical Weathering

8. Water weathers rock by dissolving it. Oxygen gas combines with iron to form rust In a process called oxidation. Carbon dioxide dissolve in rainwater and the water sinks through air pockets in the soil. The result is a weak acid called carbonic acid. This acid easily weathers limestone and marble. Agents of Chemical Weathering

9. Living organisms have roots that push into the rock. The roots produce weak acids that slowly dissolve rock around the roots. Lichens also weather rock. Acid rain causes very rapid chemical weathering. The fossil fuels pollute the air, mix with rainwater, and form acid rain. More Agents

10. The rate of weathering is determined by the type of rock and climate. The minerals making up the rock determine how fast it weathers. Some rocks are permeable and weather quicker. Chemical reactions occur quicker in higher temperatures and wetter climates. Rate of Weathering

11. Soil Formation • Soil forms as rock is broken down by weathering and mixed with other materials on the surface. • Bedrock is the solid layer beneath the soil. • As bedrock weathers, it becomes the basic material of soil.

12. Soil is made up of Rock particles Minerals Decayed organic material Air water Soil Composition

13. Soil contains humus, a dark colored substance that forms as animal and plant remains decay. When describing soil, we use different textures by size, such as, gravel, sand, silt, and clay. Soil made up of equal parts of clay, sand, and silt is loam. Soil Description

14. Crumbly mixture that holds a lot of air and water. Great for growing most types of plants. Loam

15. The particles that make up soil are classified by size. From largest to smallest they are sand, silt, and clay. Pieces larger than sand are called gravel. Soil Size

16. As soil forms over long periods of time it develops layers called horizons. This is the soil profile. A soil horizon is a layer of soil that differs in color and texture from the layers above or below it. The more evolved a soil layer is the further it is from the original bedrock. (smaller and smaller pieces) Soil Horizons

17. The A horizon is made up of topsoil, a crumbly dark brown soil that is a mixture of humus, clay, and other minerals. It is the most evolved soil. Humus is decayed organic material. Dark colored. A Horizon

18. The B horizon often called subsoil usually consists of clay and other particles wasted down from the A horizon. It has little humus. B Horizon

19. The C horizon contains only partly weathered rock. Least evolved soil. Beginning stage of soil formation as the bedrock weathers. C Horizon

20. The rate at which soil forms depends on the climate and type of rock. Weathering occurs more rapidly in areas with a warm, rainy climate. As a result soil forms more quickly in these areas. In contrast, weathering takes place slowly in areas where the climate is cold and dry. Rate of Soil Formation

21. In every cubic meter of soil live billions of organisms. All organisms enrich the soil with humus with their remains or wastes. As plants shed leaves, they form a loose layer called litter. Decomposers are organisms that break the remains of dead organisms into smaller pieces and digest them with chemicals. Earthworms break up hard compacted soil. Burrowing animals nest in the soil. Life in Soil

22. Less than 1/4th of the Earth is dry land. Except for the small amount added by volcanoes, new land cannot be created. So the land we have must be used wisely. Conserving Land and Soil

23. Types of Land Use

24. Agriculture: New land must be cleared for crops and rangeland. Development: Land cleared for cities, towns. Homes, factories and other human uses. Mining: Land used to obtain natural resources. Ways We Change the Land

25. Soil is a valuable resource as everything that lives on land depends on it. Plants grow in soil. Animals need plants for many purposes (food, habitat) Value of Soil

26. Soil is a renewable resource, but soil formation takes a long time. Takes 100’s of years for a few cm of soil to form. Thick, fertile soil can take 1000’s of years to develop. Renewable Resource

27. Soil can be exhausted (lose it fertility) by over farming. Soil can be polluted by human activity. Wind and water can erode soil and wash it out to sea. Soil Damage and Loss

28. Desertification • The advance of desert-like conditions spreading across once fertile areas. • Caused by drought, climate change, overgrazing, and the cutting down of forests.

29. In the 1800’s settlers in the Great Plains turned the fertile, moisture laden sod into farmland. In drought, this land dried up and blew away as dust. In the 1930’s, severe drought over several years allowed this soil to be blown away in great, dark clouds. Some of these dust storms reached New York City. This lasted until 1938. Many farmers in the “Dust Bowl” had to abandon their homes and move away. Dust Bowl

30. Soil Conservation • Management of soil to prevent its destruction. • Uses contour plowing, conservation plowing, crop rotation, and allowing fields to lie fallow

31. Plowing fields along the contour lines of a slope. This prevents the rain runoff from making gullies and eroding the soil away. Can reduce the soil lost to erosion by 50%. Contour Plowing

32. Farmers use machines that plow the dead stalks back into the ground. This helps hold the soil in place and fertilizes the soil. Conservation Plowing

33. Farmers rotate the crops that they plant each year. Since different plants use different nutrients, the fields can be used longer. Some plants can actually add nutrients to the soil, especially those that are plowed back under. Crop Rotation

34. This is when farmers don’t plant a field for several years to allow the soil to restore its nutrients. Fallow Fields

35. Restoring land damaged by erosion, landfills, pollution, or mining. Often involves filling in strip mines or covering landfills. Is cheaper to avoid the problem that to have to restore the land. Soil Reclamation

36. Differences in climate and the local bedrock mean that different parts of the world will have different types of soil. Scientists classify soils by climate, common plants, and the composition-whether it is rocky, sandy, or rich in clay. Soil Types

37. Soil Types in the USA

38. Form where it is cold year round. Thin soil with little humus. Tundra Soils

39. Northern Forest Soils • Forms in cool, wet climates. • Range from thick and fertile to thin with little humus.

40. Forms in cool, dry climates of the grasslands. Topsoil thick and rich in humus. Prairie Soils

41. Topsoil often thin because cold temperature slow chemical weathering. Steep slopes allow erosion to cause soil loss. Mountain Soils

42. Found in warm, wet climates. May be low in humus. Southern Forest Soils

43. Forms in areas with few plants. Little chemical weathering due to lack of rainfall Often sandy, thin soil that is low in humus Desert Soils

44. Form in wet, tropical climates Often low in humus and minerals. Tropical Soils