1. Weathering, Soil and Mass Wasting

2. Earth’s External Processes
Weathering – disintegration of rock at or near the earth’s surface
Mass wasting – transfer of material down slope in response to gravity
Erosion – transportation of material by a mobile agent such as water, wind, or ice

3. These are non–stop, never-ending processes!

4. Weathering must happen before erosion can take place!
Which comes first
Erosion or weathering?
Weathering must happen before erosion can take place!

5. Mechanical Weathering
Breakdown of bigger pieces into smaller pieces
This is also referred to as physical weathering
Only size changes occur in this process
No chemical composition change occurs in mechanical weathering

6. Weathering
Mechanical weathering – the physical breaking or fragmentation of rock into smaller pieces

7. What things can affect mechanical weathering?
-Temperature
-Most of the temperature influence comes from the freezing of H2O
-Ice expands by 9% over the volume of liquid H2O
-Freezing H2O cracks rocks

8. Frost wedging -Repeated freezing and thawing of H2O in rocks
-Can form potholes in cold climate areas
-Can be responsible for splitting trees as well

9. Biological Activity
Plant roots in search of minerals and water grow into fractures, and as the roots grow, they wedge the rocks apart. This is physical weathering.

10. Pressure -Reduced pressure is what we are talking about -Bedrock moves upward as overlying rock is removed -Bedrock expands upward -Cracks form as pressure is reduced -Cracks are called joints -Joints/cracks form parallel to the ground

11. Mechanical Weathering
Exfoliation:
Rock breaks apart in layers that are parallel to the earth's surface; as rock is uncovered, it expands (due to the lower confining pressure) resulting in exfoliation.

12. Mechanical Weathering
Many igneous rocks, particularly granite, are formed at great depth.
When they come to the surface, they expand.
Creates a morphology with exfoliation slabs – slabs sheet off in onionlike layers
Stone Mountain, Georgia
Expansion of rocks pose a risk in deep mines – explode off walls
These fractures, or joints can enhance frost wedging and other erosive processes

13. Sheet Joints (Exfoliation)

14. Half Dome, Yosemite, CA Stone Mountain, GA
Summit of Half Dome, Yosemite, shows exfoliation
Half Dome, Yosemite, CA
Stone Mountain, GA

15. Exfoliated Domes, Yosemite

16. Stone Mountain, Georgia, showing the product of exfoliation due to unloading
Summit of Half Dome, Yosemite, shows exfoliation
Stone Mountain, GA

17. Chemical Weathering of Statues, Bath, UK
Oxygen dissolved in water will oxidize some materials like nails and rocks!
(Rust)
Carbon dioxide dissolved in water forms a weak acid called carbonic acid, which helps dissolve rock material.
Chemical Weathering of Statues, Bath, UK

18. The Result of Chemical Weathering -New Minerals Are Formed and Dissolved Particles Are Released -The Amount of Chemical Weathering Is Determined by the Composition of the Parent Rock -Temperature increases leads to an increase chemical reactions

21. How Granite Weathers Potassium Feldspar + carbonic acid + water 
Chemical weathering – the alteration of the internal structure of minerals by chemical reactions
Potassium Feldspar + carbonic acid + water 
Clay mineral + Potassium bicarbonate + Silica

22. Spheroidal Weathering
Fluids enter rock along joints or fractures and the edges become rounded.

23. Factors influencing weathering: Differential Weathering
Rates of Weathering
Factors influencing weathering:
Mineral makeup
Climate
Differential Weathering
Granite versus Marble

24. Differential Weathering
Rocks weather at different rates because of different mineral makeup, degree of jointing, and exposure to the elements.
More resistant rock protrudes as ridges and pinnacles.
Bryce National Park, Utah

25. The four components of soil:
What Is Soil?
Soil is the layer of rock and mineral fragments along with organic matter, water and air that supports the growth of plants.
The four components of soil:
Decomposed rock
Humus
Air
Water

26. Dirt is what gets on your clothes and into your house
What is Dirt?
Dirt is what gets on your clothes and into your house

27. Controls on Soil Formation
Parent material – Bedrock vs. Unconsolidated
Time – longer time, more soil
Climate – temperature and precipitation
More plants and animals = more organic matter
Poorly developed soils on steep slopes

28. Soil Texture and Structure
Point A:
10% silt
40% clay
50% sand
Clay loam has no single particle size percentage that dominates!

29. Controls of Soil Formation
If the parent material is bedrock, then we get residual soils
On unconsolidated sediments, we get transported soils

30. How quickly is soil formed?
Soil composition
-Soil forms in layers
-Larger materials are found on the bottom
How quickly is soil formed?
-It may take several hundred years for 1cm to form

31. Soil profile
A vertical column showing the sequence of layers of particles in the soil

32. Soil Horizons -A distinct layer or zone within a profile
-There are four major zones (O, A, B, C)
O zone -Leaf litter, high decomposition
A Zone
-High organic matter
-Generally the darkest in color
-High humus content
B Zone
-Less developed
-Lighter in color
-Zone of accumulation (highly soluble mineral build-up)
-Red or brown in color
-Clay accumulated (Hard pan formation)
C Zone
-Contains weather parent material

33. Soil Horizons O zone -Leaf litter, high decomposition A Zone
-High organic matter
-Generally the darkest in color
-High humus content
B Zone
-Less developed
-Lighter in color
-Zone of accumulation (highly soluble mineral build-up)
-Red or brown in color
-Clay accumulated (Hard pan formation)
C Zone
-Contains weather parent material

34. Rill and Gully Erosion

35. Eroded channels ranging in size from rivulets to small gullies caused mainly by runoff waters rather than raindrop dislocation.

36. Gully erosion in Tanzania. What is the main factor for it’s cause?

37. Who cares about soil erosion?

38. Mass Wasting: The Work of Gravity
Mass wasting refers to the down slope movement of rock and soil under the influence of gravity.
Hurricane Mitch in 1998 caused severe mud flows in Central America

39. Triggers of Mass Wasting
The Role of Water
Oversteepened Slopes
Vegetation
Earthquakes

40. Flows, Slides, and Falls (All types of Mass Wasting)
Type of material, the kind of motion, and the velocity of movement dictate kind of mass movement
Falls involve the free-fall of debris or rock
Slides occur when the material remains coherent and moves along a well-defined surface
Flow occurs when material moves down slope as a viscous fluid (liquidy)

41. Mass Wasting Processes
A debris flow involves a flow of soil and regolith containing a large amount of water.

42. Mass Wasting Processes
Earthflows form on hillsides in humid areas during times of heavy rainfall.

43. Slow Movements
Creep involves the gradual downhill movement of soil and regolith.
Freeze and thaw cycles contribute to creep.

44. Slow Movements Slump Landslide movement along a curved understructure
Occur on thick soils with moderate slopes
Common after rainfalls
Mixing of debris
Crescent shaped scar on the landscape
Triggered by rain or EQ

45. The frozen bottom layer stays in place.
Solifluction
Solifluction occurs in regions of permafrost when the thawed upper region flows down slope.
The frozen bottom layer stays in place.

46. Rock Avalanches
The high speed of rock avalanches suggests that trapped air has helped them attain velocities of 125 miles per hour.

47. What does this coin have to do with Rock Falls?
"The Old Man of the Mountain" is a rock formation that can be found on Mt. Cannon in the Franconia Notch gateway to Northern New Hampshire. From the right view, this unique rock formation, comprised of five layers of Conway red granite, depicts the distinct profile of an elderly man gazing eastward. Geographers believe that the layers of granite were positioned by the melting and slipping away action of an ice sheet that covered the Franconia Mountains at the end of the glacial period - some 2,000 to 10,000 years ago. Today, the formation, measuring over 40 feet high with a lateral distance of 25 feet, is held in place by cables and turnbuckles to prevent further slipping and possible destruction.
What does this coin have to do with Rock Falls?

48. The Old Man is no more!!