1. Weathering and Erosion

2. Objective:
2.1.3
I can explain how natural actions such as weathering, erosion (wind, water and gravity), and soil formation affect Earth’s surface.

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

4. What is Mechanical Weathering?
When physical forces break rock into smaller pieces
Does not change the rock’s composition
Three Ways
Frost Wedging
Unloading
Biological Activity

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

6. Mechanical Weathering: Unloading
The uplift and weathering of rocks overlying igneous rocks
Why?
Pressure on igneous rocks is reduced causing uplift
Exfoliation: slabs of outer rock separate and break loose

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

8. What is Chemical Weathering?
Is the transfer of rock into one or more new compounds

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

10. 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

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

12. 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

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

14. 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

15. Organisms Climate Slope Furnish organic matter in 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

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

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

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

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

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

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

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

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

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

25. 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

26. What is a Glacier?
Large, moving mass of ice that forms near Earth’s poles and in mountainous regions at high elevations

27. How do Glaciers Erode Soil?
Scrape and gouge out large sections of landscape
Can carry huge rocks and piles of debris over great distance

28. Landforms Created by Glaciers
Glaciated Valley
U-shaped valley
Cirques
Bowl-shaped depression at the head of a glaciated valley, that is surrounded on three sided by steep rock walls
Arêtes
Snaking ridge
Horns
Pyramid-like peaks

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

30. 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

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

32. Objective:
2.1.4
I can explain the probability of and preparation for geohazards such as landslides, earthquakes, tsunamis, sinkholes, groundwater pollution, and flooding.

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

34. 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

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

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

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

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

39. 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

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

41. 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

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

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

44. 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