Weathering and Soil Chapter 7

1. Weathering and SoilChapter 7

2. Section 1 Weathering

3. This formation is called a “tor.”

4. WEATHERING • Weathering is a process that breaks down rock into smaller pieces. • Two different types of weathering: • Mechanical • Chemical

5. Mechanical Weathering • Mechanical weathering occurs when rocks are broken apart by physical processes. • Something has to hit, grind, or crack rock. • Things that are responsible for mechanical weathering are: • Plants and animals • Ice Wedging • Rain • Chuck Norris

6. Mechanical Weathering by Plants and Animals • Plant roots are very strong and can push rocks apart. • Animals dig and burrow, loosening sediments and bringing them to the surface to weather more. • Tiny living organisms also help break down rock.

7. Mechanical Weathering by Ice Wedging • Ice wedging occurs in climates where water enters cracks and freezes. • Water expands when it freezes, pushing rock apart. • This process repeats itself, the crack widens, and the rock eventually breaks apart.

8. Mechanical Weathering by Rain • Rain drops act as miniature hammers, pummeling the ground, breaking rock into soil.

10. Surface Area and Speed of Weathering • As rocks break apart into smaller pieces, more surfaces are exposed to weathering. • The inside of the rock is now also exposed to weathering, so weathering will occur faster.

12. Chemical Weathering • Chemical weathering occurs when chemicals break down rock or change the rock into different minerals. • These chemicals can come from • Natural acids • Plant acids • Oxygen

13. Chemical Weathering by Natural Acids • Water can chemically react with carbon dioxide and create a weak acid called “carbonic acid”—the same acid found in many soft drinks. • This acid reacts with rock that contains calcite, like limestone, and dissolves it. • Other rocks are also affected.

14. Cave Formation from Chemical Weathering • Caves form when acidic groundwater dissolves underground limestone. • Stalactites can form on cave ceilings from dripping dissolved rock. • Stalagmites can form on the floor when the drips hit.

15. Chemical Weathering from Plant Acids • Plant roots and decaying plants give off acids that can dissolve rock. • Plants thrive on the broken down rock (new soil) and take the nutrients into their roots.

16. Chemical Weathering by Oxygen • Oxidation is the process of oxygen chemically combining with other matter to change it. • Rust is caused by oxidation—oxygen combining with iron. • Many rocks contain iron and will turn reddish through oxidation. The reddish material is softer and eventually crumbles —like rust.

17. Weathering by Climate • Climate is the pattern of weather in an area over many years. • Warm, wet climates cause weathering to happen more quickly. • Chemical reactions happen faster with water and heat. • Cold, dry climates slow weathering down.

18. How Climate Affects Different Types of Rock • Soft rocks break down easier in wet climates. • Limestone • Marble • Hard rocks don’t allow water to soak in as much, so they are harder to weather in wet climates. • Granite • Basalt

19. Section 2 The Nature of Soil

20. Soil Formation • Five things affect soil formation: • Climate • Types of parent rock • Slope of land • Types of vegetation in the area • Amount of time rock has been weathering

21. Climate

22. Parent Rock

23. More on ParentRock

24. Slope of the Land

25. Type ofVegetation • The type of minerals in a rock will affect the type of vegetation that forms in an area. • The type of vegetation then affects the type of soil that will form.

26. Time • It takes time for weathering to take place. Time

27. THE NATURE OF SOIL • Soil is a mixture of weathered rock, decayed organic matter, mineral bits, water, air, and living organisms. • Can take thousands of years to form • Decayed organic matter turns into nutrient rich material called humus. • Humus comes from the decay of a layer of material on the surface called litter. • Includes leaves, twigs and other dead organisms • http://www.ucopenaccess.org/courses/APEnvSci/course%20files/multimedia/lesson17/animations/2c_soil_formation.html

28. How Soil Forms • Parent rock begins to break down through chemical and mechanical means. • Organisms begin to grow in and on rock, further breaking it down. • As the organisms die, they add nutrients to the soil (humus). • Rain carries dissolved nutrients down into the soil layers (leaching).

29. Soil Profile • Make-up of different layers of soil • Horizon O – top organic layer—humus. • Horizon A—top layer of soil. • Fertile layer with more humus and less rock and mineral particles than other soil horizons • http://courses.soil.ncsu.edu/resources/soil_classification_genesis/soil_formation/soil_transform.swf

31. Horizon B • Horizon B – middle soil layer • Contains less humus and is lighter in color than A horizon • Minerals travel from A horizon to B horizon in a process called leaching.

32. Horizon C • Bottom layer • Has very little organic matter and is not strongly affected by leaching • Contains rock – the parent material of the soil • Soil Formation Animation

33. Glacial Deposits • Glaciers deposit sediments when they melt. • These types of soils are extremely fertile. • http://mrbdc.mnsu.edu/mnbasin/flash/glaciers/glaciation_animation.html • Soil from one place is moved to another by glaciers. • http://www.wwnorton.com/college/geo/egeo/flash/18_1.swf • http://www.brainpop.com/science/earthsystem/glaciers/

34. Soil Types • Different climates yield different types of soils • Prairie soils have thick, dark A horizons because grasses there leave lots of organic matter. • Temperate forests, like those in the eastern US have thinner A horizons than prairies. • Deserts usually contain little organic matter and upper horizons are thinner than in wetter regions.

35. Other Factors • Type of parent material will dictate what types of soils come from it. • Basalt will yield clay soils. • Sandstone yields sandy soils. • Time is a factor. • The longer weathering has been going on, the more soil will have developed in the area. • The slope of the land is important in how soils develop. • Slopes often lose their soil due to gravity. • Soil is often deposited thickly at the bottom of a slope. • This soil in bottomlands is often moister, too, due to water settling at the bottom of a slope due to gravity.

36. Deposits at the base of hills and mountains • Called alluvial fans

37. Section 3 Soil Erosion

38. So, What’s the Big Deal About Soil? • Soil is important because we grow our crops in soil. • We eat the crops. • We eat animals that ate the crops. • If soil is gone or damaged, we don’t get as much food from the soil.

39. Erosion • http://www.youtube.com/watch?v=w7yis7nlczs (Dust Bowl Days)

40. Causes of Soil Erosion • Agriculture Cultivation • Farming methods in the past contributed to soil erosion. • Areas with lost soil need more chemical fertilizer, which contributes to soil damage.

41. Causes of Soil Erosion • Forest Harvesting • When trees are removed, soil is exposed to weathering and erosion. • Large amounts of soil can be lost if new trees or other vegetation aren’t planted in place of the harvested trees. • Tropical rainforests are often cleared by burning. • Farming the land then increases chances for soil loss.

42. Causes of Soil Erosion • Overgrazing • If livestock are allowed to graze too long in the same pasture, there are no more grass roots to hold the soil in place. • Soil erosion is more likely to take place.

43. Effects of Soil Erosion • Eroded land can erode even further. • Eroded sediments can clog streams.

44. Effects of Erosion • The effects of strip mining can be mountaintop erosion.

45. Preventing Soil Erosion • Farmers can use proper grazing methods. • Farmers can use terracing. • Terracing stair-steps the land so that water does not flow straight downhill. • Farmers can use contour farming. • Farming around hills instead of up or down them. • The furrows slow down the water as it flows downhill. • Farmers can use no-till or low-till farming methods. • Land is not tilled or tilled very little so that root systems are left in place.

46. Preventing Soil Erosion • Construction workers can keep areas moist to prevent soil from blowing away. • Plants can be planted immediately after construction is complete. • Topsoil treatments can be put in place to hold soil down until plants grow. • Rocks and rip-rap can hold hillsides in place.

47. Lay down straw to hold soil in place until plants grow.

48. Preventing Soil Erosion Farmers and others can plant shelter belts (wind breaks) of trees and bushes around fields vulnerable to erosion Shelter belts slow down the effects of the wind.

49. Terraces

50. Contour Farming • Farming around hills