1. Weathering & Erosion

2. Weathering
The breaking down of rock.

3. Physical (or mechanical) Weathering
Physical (or mechanical) breakdown: it is the mechanical breakdown of rock or minerals. It only breaks the rock or mineral into smaller pieces, the composition of the material is NOT changed!!

5. Physical (Mechanical) Weathering
There are several different types of physical weathering:
1.) Frost or Ice Wedging –The breaking down of rock by the force exerted by water expanding as it freezes into ice.

6. Water expands as it freezes, this breaks the rock into angular fragments.

7. Frost Wedging animation
This occurs A LOT in Western New York –because we have alternating freezing and thawing of moisture in rock openings, causing rock disintegration, in other words POTHOLES.
This will ONLY occur in areas where the temperature alternates above freezing and below freezing!
Frost Wedging animation

8. 2.) Exfoliation
Exfoliation – Erosion of upper rock causes underlying rock to expand resulting in cracking and peeling of rock in slabs.
Think of onion skin layers and peeling them off.

9. PHYSICAL WEATHERING EXFOLIATION – PEELING AWAY OF ROCK
due to unloading (reduced pressure at earth’s surface) or fluctuations in temperature. Rocks expand and crack

10. PHYSICAL WEATHERING - EXFOLIATION

11. Stone Mountain, Georgia- exfoliation has caused an overall rounded shape to the mountain.

12. 3.) Organic Activity (plant and animal)
Organic Activity – plant roots or animals like burrowing worms can cause rock to breakdown.

13. PHYSICAL WEATHERING – ROOT ACTION
PLANT ROOTS UPLIFT AND FRACTURE ROCK

14. 4.) Wetting/Drying
Wetting and Drying - addition of water to mineral structure causes structure to expand.
Mudcracks form from the wetting and drying of clay material.

15. Important!
What happens to the erosion rate when you increase the surface area?
Physical weathering increases the surface area of rocks/minerals.
Taking a rock/mineral and breaking it up into smaller pieces causes it to take up more space (surface area) and will eventually increase the rate of chemical weathering to occur.

17. Physical Weathering occurs
Let’s Work This Through!
Starting Volume:_______________ Volume:________________________
Total Surface Area:____________ Surface Area:__________________
(2 feet)3 = 8ft3
(2 feet)3 = 8ft3
6 x (2ft)2=24ft2
6 x (1foot)2 x 8 = 48ft2

19. Chemical weathering: is the decomposition of material.
The composition IS Changed!
Oxidation: iron turns RED!

20. Chemical Weathering

21. 1.) Hydrolysis
Hydrolysis – the chemical reaction between water and other substances.
Silicate minerals will often form clay from this process.
Kaolin mine, central Georgia (feldspar weathered into clay by hydrolosis)

22. Hydrolysis cont…
Halite, gypsum, and limestone are most susceptible to becoming weathered by water, and most compounds are at least slightly soluble in water, so water is called the universal solvent.
Chemically Weathered Limestone

23. 2.) Carbonation
Carbonation (Carbonic Acid) – dissolving of substances by acids in water often leaving insoluble remains.
Carbonic Acid can devastate rocks made of calcite. Rocks such as limestone and dolomite can be entirely dissolved, leaving extensive caverns.

24. Caves formed from Carbonation

25. 3.) Oxidation
Oxidation – chemical reaction of a substance with oxygen causing a rust material to form.
Note: Most rocks/minerals containing iron will appear RED in color after an oxidation reaction.
Oxidation of Sandstone

26. Climate and Weathering
Climate plays a very important role in weathering.
The temperature and amount of moisture influences the type of weathering that will occur.
Warm and wet climates produce mostly chemical weathering. Never any frost wedging.
Cool and slightly wet climates produce mostly physical weathering.

27. Factors Effecting Weathering Rate
Low
Highly resistant minerals
Massive rocks (big blocks)
Little to no rainfall
Low temperatures
Little or no soil
Little organic activity
Medium
Moderately resistant minerals
Average rock size
Some rainfall
Medium temperatures
Soil is present
Organic activity is moderate
High
Unstable minerals (easily broken down)
Small rock particles
Heavy rainfall
High temperatures
Thick soils
A lot of organic activity

28. 80 years later: look what’s happened
Cleopatra’s Needle
80 years later: look what’s happened
Cleopatra’s Needle in Egypt: warm, dry climate, little to not weathering occurs.
Cleopatra’s Needle was moved to New York and has weathered significantly on only 80 years due to: cold and wet climate

29. Weathering and Resistance
The harder the rock or mineral is, the more resistant it will be to weathering.
Any rock with quartz will be quite resistant due to quartz’s hardness.
Rocks made mostly of calcite, a very soft mineral, will be easily weathered.

30. WHAT KIND OF CLIMATE SUPPORTS WEATHERING?
HIGH
PPT ↑
LOW
COLD →→→→→→→→→→ HOT

31. CLIMATE CONTROLS WEATHERING
PHYSICAL WEATHERING:
COLD AND MOIST
ALTERNATE FREEZE / THAW
CHEMICAL WEATHERING:
WARM AND MOIST
IN BOTH CASES – WATER IS THE PRIMARY INGREDIENT THAT PROMOTES WEATHERING

34. WHICH LAYER IS MORE RESISTANT TO WEATHERING? LEAST RESISTANT?D C B

35. THE END PRODUCTS OF WEATHERING
The end products of weathering are sediments. They can be pieces that range in size from boulders to silt…

36. Do I have to say it?

37. Or they can be ions in solution

38. WEATHERING SUMMARY WEATHERING IS THE BREAKDOWN OF ROCK INTO SEDIMENTS
PHYSICAL WEATHERING – INCREASES SURFACE AREA - COLD/HUMID CLIMATE
CHEMICAL WEATHERING – WARM/HUMID CLIMATE
IN BOTH CASES, WATER IS THE PRIMARY INGREDIENT

39. Erosion
the removal and/or transport of material by 5 possible agents: running water, glaciers, waves, wind, and gravity.

40. Five Agents of Erosion are:
1- Water
2- Wind
3- Waves
4- Glaciers
5- Gravity
A good way to remember these are:

41. We also have to remember that humans and animals may also play a part in erosion