1. Weathering and Erosion 2013By 6C

2. Old and New Mountains
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.
The Appalachians are much older so they have had more time to weather and erode.

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

4. Physical/Chemical Changes
In a physical change, the original substance still exists, it has only changed in form. Examples are tearing paper in half, ice melting, sugar dissolving in tea.
In a chemical change, a new substance is produced. Examples are the burning of paper, iron rusting, milk going sour.

6. Mechanical/Physical Weathering
Mechanical (physical) 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.

7. Abrasion
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.
The primary method of physical weathering.

8. 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.

9. Ice Wedging Chapter 10 Section 1 Weathering
Click below to watch the Visual Concept.
Visual Concept

10. Chemical Weathering
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!

11. Agents of Chemical Weathering
Water weathers rock by chemically 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.

12. Oxidation Chapter 10 Section 1 Weathering
Click below to watch the Visual Concept.
Visual Concept

13. More Agents
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.

14. Differential Weathering Section 2
What Is Differential Weathering? Differential weathering is a process by which softer, less weather resistant rock wear away and leave harder, more weather resistant rock. The image below is an example of differential weathering.

15. Rate of Weathering
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.

16. The Shape of Rocks
Surface Area The more surface area of a rock that is exposed to weathering, the faster the rock will be worn down.
Increasing the Rate of Weathering If a large rock is broken down into smaller fragments, weathering of the rock happens much more quickly.

17. Weathering and Climate
What Is Climate? Climate is the average weather condition in an area over a long period of time.
Temperature and Water The rate of chemical weathering happens faster in warm, humid climates. Water also increases the rate of mechanical weathering.

18. Weathering and Elevation
High Elevations Rocks at higher elevations, as on a mountain, are exposed to more wind, rain, and ice than rocks at lower elevations.
Steep Slopes The steepness of mountain slopes increases the effects of mechanical and chemical weathering. Steep slopes cause water and sediments to quickly run down the side of the mountain.

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

20. 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.

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

22. Loam
Rich, fertile soil that is made up of about equal parts of sand, silt, and clay.
Crumbly mixture that holds a lot of air and water.
Great for growing most types of plants.
Farmers love this type of soil.

23. Soil Sizes
The particles that make up soil are classified by size (texture).
From largest to smallest they are gravel, sand, silt, and clay.

24. Soil Description
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.

25. Regolith
A term that describes the weathered material that is on top of the bed rock
Top soil is the top layer of regolith

26. Soil Properties
Soil Fertility A soil’s ability to hold nutrients and to supply nutrients to a plant is described as soil fertility.
Soil Horizons Because of the way soil forms, soil often ends up in a series of layers called horizons.
Soil pH Soils can be acidic or basic. The pH scale is used to measure how acidic or basic a soil is.

27. Soil Layers

28. Leaching Chapter 10 Section 3 From Bedrock to Soil
Click below to watch the Visual Concept.
Visual Concept

29. Residual and Transported Soil
Chapter 10
Section 3 From Bedrock to Soil
Residual and Transported Soil
Click below to watch the Visual Concept.
Visual Concept

30. Soil Horizons
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) R

32. A Horizon
The A horizon is made up of topsoil, a crumbly dark soil that is a mixture of humus, clay, and other minerals.
It is the most evolved soil.
Humus is decayed organic material.
Usually dark colored.
Most fertile layer.

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

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

35. Soil Triangle
A soil texture triangle is used to classify the texture of a soil.
The sides of the soil texture triangle are scaled for the percentages of sand, silt, and clay.
Clay percentages are read from left to right across the triangle
Silt is read from the upper right to lower left
Sand from lower right towards the upper left portion of the triangle
. The intersection of the three sizes on the triangle give the texture class. For instance, if you have a soil with 20% clay, 60% silt, and 20% sand it falls in the "silt loam" class.  

36. Rate of Soil Formation
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.

37. Soil Conservation
Methods of maintaining the fertility of soil by protecting the soil from erosion and nutrient loss.
Plants are used to cover the ground and prevent erosion.
Farmers are taught not to overgraze or overuse the land when planting crops which prevents soil depletion.

38. Conserving Land and Soil
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.

39. Types of Land Use

40. Ways We Change the Land
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.

41. Life in Soil
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.

42. Value of Soil
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)

43. Renewable Resource
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.

44. Soil Damage and Loss
Soil can be exhausted (lose its fertility) by over farming (over use/depletion).
Soil can be polluted by human activity.
Wind and water can erode soil and wash it out to sea (erosion).

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

46. Dust Bowl
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 Many farmers in the “Dust Bowl” had to abandon their homes and move away.
Read Steinbeck’s “The Grapes of Wrath”

47. Providence Canyon
Providence Canyon is near Lumpkin, Georgia.  It has beautiful gullies formed by erosion 150 years ago. This park is part of Georgia's East Gulf Coastal Plain region. People call it Georgia's "Little Grand Canyon."  There are 16 canyons altogether.  Some canyons are 1 mile long and 300 feet across.  An ancient ocean formed all the canyons.

48. Georgia Red Clay Georgia is famous for its red clay.
This red color comes from the high iron content in the soil.
Think rust!

49. Soil Conservation Methods
Management of soil to prevent its destruction through erosion or soil depletion.
Uses contour plowing, terracing, conservation plowing, crop rotation, cover crops, and allowing fields to lie fallow.

50. Prevents erosion and soil depletion
Cover Crops
Plants grown to suppress weeds, help build and improve soil, and control diseases and pests.
Are also called "green manure" and "living mulches."
They're called "green manure" because they provide nutrients to the soil much like manure does. And as "living mulches," cover crops prevent soil erosion.
Once grown, cover crops are usually mowed and then tilled back into the soil.
Prevents erosion and soil depletion

51. Contour Plowing 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%.
Prevents erosion

52. Terracing
Used on very steep hills. Changes a steep hill into many, smaller, flatter hills.
Prevents erosion

53. Wind Breaks
Prevents erosion
Rows of trees or shrubs planted along the edge of a field to protect the soil from wind erosion.

54. No Till Plowing
By not making furrows, the ground is less prone to erosion.
Farmers use machines that plow the dead stalks back into the ground.
This helps hold the soil in place and fertilizes the soil.
Also called conservation plowing.

55. Prevents soil depletion
Crop Rotation
Prevents soil depletion
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.

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

57. Soil Reclamation
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.

58. Soil Types
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.

60. Soil Types in the USA

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

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

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

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

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

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

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