1. Weathering, Erosion & Deposition

2. THINK!!!!
Imagine the tiniest rock you have ever found. How did it get so small? It didn’t start out that way! What forces created this rock?

3. Weathering is the breaking down of rocks and other materials on the earth’s surface

4. What is the difference between weathering and erosion?

5. Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down by air, water, plants and animals
Erosion - process of removing Earth materials from their original sites through weathering and transport by water, wind or gravity

6. What are the two types of weathering?

7. Mechanical/Physical Weathering
2 Types of Weathering
Mechanical/Physical Weathering
processes that break a rock or mineral into smaller pieces without altering its composition
Chemical Weathering processes that change the chemical composition of rocks and minerals

8. What is Mechanical/Physical Weathering?
A rock is physically changed without a
change in chemical composition
Processes include:
Frost Action / Ice Wedging
Abrasion by wind and water
Plant and Animal Action
Thermal Expansion and contraction
Pressure Unloading / Exfoliation

9. Frost Action / Ice Wedging
Alternating freezing and thawing of water causes material to break up
Example – Pot holes, Ice cubes in an ice tray
Water expands between 4 and 0 degrees Celsius
Volume increases by 9%!!!!
The Bigger the crack gets, the more water it lets in……causing a snowball effect

11. Frost Action / Ice Wedging

12. Abrasion
Wearing down or smoothing of a material due to constant collisions
Example – Beach glass, sandblasting
Breakdown caused by friction
Rocks become rounded
Waterfalls may result

13. Abrasions

14. Plant and Animal Action
Plant root growth and uplift fracture rocks
Animals burrowing also cause breakdown of rocks
Actions also increase the exposure of rocks to air and water

15. Plant Action

16. Lichen (moss) on a rock or growth of tree out of the rock

17. Animal Action

18. Thermal Expansion and Contraction
Extreme changes in temperature may cause cracking

19. Pressure Unloading / Exfoliation
Cracking at weak joints due to a release of pressure
Cause and effect of Exfoliation
Rock breaks off into leaves or sheets along joints which parallel the ground surface
Expansion of rock due to uplift and erosion
removal of pressure of deep burial
Occurs often in bedrock when glaciers recede

21. Exfoliation
Peeling away of surface layers, caused by changes in temperature, pressure or vegetation (trees, grass, vegetation growing on rocks.)
Roots wedge into pores and cracks, splitting the rock

22. Dome Exfoliation

23. What is Chemical Weathering?
The Chemical composition of
the rock is altered causing a change
in properties
Processes include:
Hydrolysis
Oxidation
Acid Reactions / Carbonation

24. Hydrolysis Reaction of water with other substances
Change is a very slow process
Examples are:
Feldspar  Kaolinite
Anhydrite  Gypsum

25. Kaolin mine in Central Georgia

26. Where Oxygen combines with other substances to produce rust
Oxidation
Where Oxygen combines with
other substances to produce rust
Oxidation in the presence of water takes
on a
reddish- yellow brown color

27. Oxidation of basalt

28. Acid Reactions / Carbonation
Carbon reacts with other substances to alter the chemical makeup of rocks
Example: Carbonic acids (water + carbon dioxide) dissolve limestone which can results in the formation of underground caves
Nitric acids produced by the decay of organic material can alter soil composition

29. Caves are formed when Carbonic Acid dissolves limestone

30. Stalactites (from the top) and Stalagmites (from the bottom) are formed in a limestone cave as a result of Chemical Weathering

31. Acid Rain has a drastic effect on rocks!

32. Nitric Acids in Soil
When organisms or plants decay Nitric Acid is produced. This is absorbed into the soil and the chemical make-up of the soil has been changed.

33. Differential Weathering
The variable rate of which rocks weather is called differential weathering
Factors affecting the rate of weathering include:
Composition (granite vs. limestone)
Climate (hot, wet, cold, dry)
Rock size (surface area)

34. Rocks weather at different rates due to. differences in mineral
Rocks weather at different rates due to differences in mineral composition. The harder
the rock, the slower the
rate of weathering is.
Some minerals are more Stable at the earth’s surface than
others! These take
longer to weather.
Composition dictates
hardness which determines
resistance to weathering.

35. The climate that a rock is in is a factor in the rate of weathering.
Cold Climates– mechanical weathering breaks down rocks rapidly
Warm, wet climates –
chemical weathering breaks down rocks rapidly

36. How much exposed area of the rock will also effect weathering
In which shape will weathering occur faster?

37. EROSION/DEPOSITION
The process of removing Earth materials from their original sites through weathering and transport agents or forces
Transport Agents or Forces include:
Water (Rain, streams, rivers, oceans, and ice/glaciers)
Wind
Gravity

38. Stream Erosion and Deposition

39. Streams

40. Glaciers

41. Wind Transport of Dust

42. Wind Transport of Dust

43. Gravity

45. Deposition Formations

46. Delta Formation from Deposition

47. Alluvial Fan from Deposition

48. What is the difference between Weathering and Erosion?
REVIEW
What is the difference between
Weathering and Erosion?
Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down by air, water, plants and animals
Erosion - process of removing Earth materials from their original sites through weathering and transport by water, wind or gravity

49. REVIEW- 2 Types of Weathering
Mechanical/Physical Weathering - A rock is physically changed without a change in chemical composition
Frost Action / Ice Wedging Alternating freezing and thawing of water causes material to break up
Abrasion by wind and water Wearing down or smoothing of a material due to constant collisions
Plant and Animal Action Plant root growth and animals burrowing increase the exposure of rocks to the air and water and causes breakdown
Thermal Expansion and contraction Extreme changes in temperature causes cracking
Pressure Unloading / Exfoliation Earth’s forces can push rock that formed deep underground up to the surface. The pressure causes the rock to expand and crack. This leads to exfoliation.
Mechanical/Physical Weathering - In the natural process of mechanical weathering, physical forces split rocks apart but do not change their composition (like smashing a walnut).

50. REVIEW -2 Types of Weathering
Chemical Weathering - Processes that change the chemical composition of rocks and minerals
Hydrolysis Water is very slow reaction and the main cause of chemical weathering.
Oxidation Where Oxygen combines with other substances to produce rust
Acid Reactions / Carbonation Carbon reacts with other substances to dissolve and alter the chemical makeup of rocks forming caves. Nitric acid produced by the decay of organic material can alter soil composition

51. REVIEW (Continued)
Differential Weathering - The variable rate of which rocks weather is called differential weathering. Most weathering occurs over long periods of time- hundreds, thousands, or even millions of years.
Factors affecting the rate of weathering include:
Composition (granite vs. limestone) What minerals a rock is made from
Climate (hot, wet, cold, dry) hot, wet regions weather rocks faster than cold, dry ones
Rock size (surface area) How large or small a rock’s surface is