1. Weathering, Soil, and Mass Movement

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

3. What is Mechanical Weathering?
Mechanical Weathering: Physical forces break rock into smaller and smaller pieces without changing the rock’s mineral composition.

4. Three Types of Mechanical Weathering
Frost Wedging
Unloading
Biological Activity

5. Frost Wedging Expansion of freezing water in cracks and crevices
Eventually breaking rocks into pieces
Sections of rock that are wedged loose are called talus

6. Unloading
The uplift and erosion of rocks overlying igneous rocks because pressure on igneous rocks is reduce
Exfoliation—slabs of outer rock separate and break loose

7. Biological Activity
The activity of organisms, including plants, burrowing animals, and humans
Plant roots wedge into rocks breaking them apart

8. What is Chemical Weathering?
Chemical weathering: the transformation of rock into one or more new compounds.

9. Agents and Evidence of Chemical Weathering
Water: most important agent of chemical and mechanical weathering. It picks up CO2 and SO2 in the air which forms acid rain.
Granite: Weathering of potassium feldspar produces clay minerals, soluble salt (potassium bicarbonate), and silica in solution. Quartz remains unaltered.

10. Silicate Materials and Spheroidal Weathering
Weathering of Silicate Minerals: Produces insoluble iron oxides and clay minerals
Spheroidal Weathering: Causes the corners and edges of rock to be more rounded

11. Rate of Weathering How fast the rocks erode Two factors
Rock characteristics
Mineral composition and solubility
Climate
Temperature and moisture
Favors high temperature and abundant moisture

12. Soil Soil: part of the regolith that supports the growth of plants.
Regolith: layer of rock and mineral fragments that covers most of Earth’s land surface.

13. How is Soil Formed?
Soil is formed by rock being eroded away.

14. Parent material Residual soil Transported soil
parent material is the bedrock
Transported soil
parent material has been carried from elsewhere and deposited

15. Characteristics of Soil
Soil Composition
Soil has four major components
A. Mineral matter (broken-down rock)
B. Humus (decayed remains of organisms)
C. Water
D. Air

16. Characteristics of Soil
Soil Texture
Texture refers to the proportions of different particle sizes.
A. Sand (large size)
B. Silt – feels like flour
C. Clay (small size)
D. Loam (a mixture of all three sizes) is best suited for plant life.

17. Characteristics of Soil

18. Characteristics of Soil
Soil Structure
Soil particles clump together to give a soil its structure.

19. Time, Climate, Organisms and Slope
Important in all geologic processes.
The longer a soil has been forming, the thicker it becomes.
Climate
Greatest effect on soil formation
Organisms
Furnish organic matter to soil
Slope
Steep slopes often have poorly developed soils.

20. Soil Profile O Horizon: Humus A Horizon: Topsoil
E Horizon: Eluviation layer
B Horizon: Subsoil
C Horizon: Regolith
R Horizon: Bedrock

21. Soil Types Soil Types Location Contents Pedalfer Pedocal Laterite
under forest vegetation
iron oxides and aluminum-rich clays in the B horizon
Pedocal
drier grasslands
Calcium carbonate
Laterite
Hot, wet, tropical climates
Intense chemical weathering to the top layers of soil

22. How does water erode the soil?
Rain uses gravity as a force to move soil.
Flash flooding and runoff of water causes erosion
Strong winds move particles

23. Processes of Water Erosion
Sheet erosion -
Rills (tiny streams)
Gullies (trenches)
Transports sediments for deposits.

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

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

26. Triggers of Mass Movement
Water
Heavy rains and rapid melting of snow
Oversteepened Slopes
The steeper the slope the greater the chance for movement
Removal of vegetation
Roots keep the soil intact. Removing plants causes erosion
Earthquakes
Aftershocks dislodges rocks causing movements

27. Classification of Mass Movements
Rockfalls occurs when rocks or rocks fragments fall freely through the air.

28. Classification of Mass Movements
Avalanches
--extremely rapid movement of earth material or snow

29. Classification of Mass Movements
Slides
In a slide, a block of material moves suddenly along a flat, inclined surface.
Slides that include segments of bedrock are called rockslides.

30. Classification of Mass Movements
Slumps
A slump is the downward movement of a block of material along a curved surface.

31. Classification of Mass Movements
Flows
Flows are mass movements of material containing a large amount of water.
Mudflows move quickly and carry a mixture of soil, rock, and water that has a consistency of wet concrete.
Earthflows move relatively slowly and carry clay-rich sediment.

32. Classification of Mass Movements
Creep is the slow, downhill movement of soil and regolith.
 slowest type of mass movement