1. Weathering and Erosion

2. What is Weathering?
Is the breaking down and changing of rocks near Earth’s surface
Two Types
Mechanical
Chemical

3. What is Mechanical Weathering?
When physical forces break rock into smaller pieces without changing the rock’s composition
Three Ways
Frost Wedging
Unloading
Biological Activity

4. Mechanical Weathering: Frost Wedging
Water enters cracks and crevices in rocks
Water freezes expanding the cracks
Eventually breaking rocks into pieces

5. Mechanical Weathering: Unloading
The uplift and weathering of rocks overlying igneous rocks because pressure on igneous rocks is reduced causing uplift
Exfoliation: slabs of outer rock separate and break loose

6. Mechanical Weathering: Biological Activity
Activities of living organisms
Plant roots wedge into rocks, breaking them apart

7. What is Chemical Weathering?
The transfer of rock into one or more new compounds

8. Agents of Chemical Weathering
Water
Most important agent
Oxygen
Causes oxidation of metal minerals
Ex: rusting
Carbon Dioxide
Combines with water in the atmosphere
Causes acids to form like in acid rain

9. Chemical Weathering in Action
Granite
Minerals turns into clay
Washed away with water
Spheroidal Weathering
Causes the corners and edges of rock to be rounded

10. Rate of Weathering What affects it?
Rock Characteristics
Mineral composition
Mineral solubility
Climate
Temperature and moisture
Favors high temperatures and abundant moisture

11. What is Soil? Part of the regolith that supports the growth of plants
Layer of rock and mineral fragments that cover most of Earth’s land surface

12. How is Soil Formed? Weathering of rocks that is carried away Factors
Parent Material
Time
Climate
Organisms
Slope

13. Soil Formation Factors
Parent Material
Source of the mineral matter in the soil
Time
Important in all geologic processes
The longer a soil has been forming, the thicker it becomes

14. Organisms Climate Slope Furnish organic matter to soil
Steep slopes often have poorly developed soils
Climate
Greatest effect on soil formation
Influences of temperature and precipitation affect rate, depth and type of weathering

15. Characteristic of Soil: Soil Composition
45% mineral matter
25% air
25% water
5% humus
Decayed remains of organisms

16. Characteristic of Soil: Soil Texture
Refers to the proportions of different particle sizes
Sand (large size)
Silt (feels like flour)
Clay (small size)
Loam (a mix of all three; best for plants)

17. Soil Texture Triangle 60 20 40 10 70 Percent Clay Percent Silt
Percent Sand
Texture Type 60 20 40 10 70

18. Characteristic of Soil: Soil Structure
Clumping together of the particles

19. Soil Types Pedalfer Pedocal Laterite Forest areas Drier grasslands
Hot, wet, tropical climates

20. What is Erosion?
Removal and transport of weathered material from one location to another

21. Agents of Erosion Running Water Wind Glaciers Ocean currents and Waves
Biological Organisms

22. What happens to the Material?
Deposition
Materials are dropped in another location
Final stage of erosion

23. How does Water Erode Soil?
Rain uses gravity as a force to move soil down a slope

24. Process of Water Erosion
Sheet Erosion
Thin surface of water moving soil particles
Rills
Tiny streams
Gullies
Trenches
Each move the soil a small distance

25. How does Wind Erode Soil?
Strong in areas of little vegetation cover
Picks up and carry sediment
These particle batter other structures

26. Landscapes Shaped by Wind
Sand Dunes
Mounds or ridges of sand
Wind also can cause them to move
Loess
Windblown silt that blankets the landscape

27. How can humans control erosion?
Planting rows of trees called windbreakers
Terracing hillsides
Plowing along the contours of hills
Rotating crops

28. What is Mass Movement?
The transfer of rock and soil down-slope due to gravity

29. Triggers of Mass Movement
Water
Heavy rain and rapid snow melting saturate the surface
Particles slid past one another easier
Over-steepened Slopes
The steeper the slope, the greater the chance for movement

30. Removal of Vegetation Earthquakes Roots keep soil intact
Removing plants increase chances of movement and erosion
Earthquakes
Dislodge rocks and minerals

31. How to Classify Mass Movement?
Classified by
Kind of material the move
How it Moves
Speed of movement

32. Types of Mass Movement Rock falls Slides Slumps Flows Avalanches Creep
Rockslides
Landslides
Slumps
Flows
Mudflow
Earthflow
Avalanches
Creep

33. Rock falls
When rock or rock fragments fall freely through the air

34. Slides
A block of material moves suddenly along a flat, inclined surface
Rockslides
Include segments of bedrock
Landslides
Movement of relatively thin block of loose soil, rock and debris

35. Slumps
Downward movement of block of material along a curve surface

36. Flows
Containing a large amount of water which move downslope as a thick fluid
Mudflow
Swiftly moving mixture of mud and water
Earthflow
Moves relatively slow
Carry clay-rich sediment

37. Extremely rapid movement of Earth material or snow
Avalanches
Extremely rapid movement of Earth material or snow

38. Creep Slow, downhill movement of soil
Only noticeable over long period time
Slowest type of mass movement

39. Preventive Actions Dig series of tranches to divert running water
Constructing protective fences on highways
Retaining walls for weak slopes
Don’t build on steep slopes