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

2. WEATHERING
Definition: The physical and chemical processes that break down rock on earth’s surface.

3. 2 Types of Weathering ROCK AFTER WEATHERING (just smaller)
PHYSICAL/ MECHANICAL WEATHERING – rocks are broken apart increasing the surface area.
ROCK BEFORE WEATHERING =
ROCK AFTER WEATHERING (just smaller)
CHEMICAL WEATHERING – Chemical reactions CHANGE minerals.
ROCK BEFORE WEATHERING ≠ ROCK AFTER WEATHERING

4. PHYSICAL WEATHERING INCREASES SURFACE AREA
MORE CHEMICAL WEATHERING CAN OCCUR

6. There are four main sources of power for mechanical weathering.
Gravity, Water, Wind, & Waves
Of these, water appears to be the leader in changing the surface.

7. PHYSICAL WEATHERING FROST ACTION – FROST WEDGING
MOST IMPORTANT IN OUR CLIMATE
FROST ACTION – FROST WEDGING
ALTERNATE FREEZE AND THAW
Water expands when frozen

8. ROCKS ARE CRACKED BY WATER FREEZING

9. EXAMPLES: POT HOLES AND FROST HEAVES

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

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

13. Powerful plant roots grow into rock cracks and cause fractures.
Root Penetration
Powerful plant roots grow into rock cracks and cause fractures.

14. PHYSICAL WEATHERING - ABRASION
ROCK PARTICLES GRIND AGAINST ONE ANOTHER
WATER
WIND

15. Abrasion
Both wind and water can cause abrasion as rock fragments bounce off each other.

16. Abrasion
This “moon looking” picture of an Antarctic rock, shows weathering from the wind blown sands.

17. PHYSICAL WEATHERING EXFOLIATION – PEELING AWAY OF ROCK
Unloading – due to reduced pressure at earth’s surface rocks will expand but they will crack because they are brittle
Fluctuating Temperatures will cause rocks to contract and expand causing cracks Examples: deserts and mountains

18. PHYSICAL WEATHERING - EXFOLIATION

19. Unloading and Exfoliation of Igneous Rocks

20. Dome Exfoliation

21. Exfoliation domes form as the slabs of rock slip or slide off the bedrock. E.g. Yosemite

22. Glaciers and avalanches can cause weathering as ice and rock interact.
Glacial Weathering
Glaciers and avalanches can cause weathering as ice and rock interact.

23. Other Agents of Weathering
Things like flash floods, mud slides, landslides, and other forms of mass wasting can cause weathering.

24. Chemical
Weathering

27. EXAMPLES OF CHEMICAL WEATHERING
OXIDATION OCCURS when free oxygen combines chemically with metallic elements (usually iron)
AKA RUST

28. 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

29. CARBONATION
Water containing carbonic acid dissolves minerals (all rain water is slightly acidic)
Most strongly affected are calcite minerals:
limestone and marble

30. CARBONATION
Stalagmites and stalactites

32. CARBONATION – SINK HOLES
Karst Topography
forms caves, caverns,
and sinkholes

33. CAVES AND SINK HOLES

34. 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

35. CHEMICAL WEATHERING HYDRATION
OCCURS WHEN Water combines with minerals – most often in granite (mica and feldspars) to form CLAY

36. Chemical
weathering

37. 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

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

39. Differential Weathering due to Climate and Composition
Masses of rock do not weather uniformly due to regional factors and composition.
Results in many unusual and spectacular rock formations and landforms

40. 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

41. More resistant rock on top

42. Factors influencing weathering:
Rates of Weathering
Factors influencing weathering:
Mineral makeup
Granite versus Marble

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

44. YOU MIGHT ALSO SEE IT LIKE THIS.

45. WHICH DIAGRAM IS AN ARID CLIMATE? HUMID CLIMATE?B
Humid – more rounded
Arid – more angular

46. Weathering Review Chemical
Rocks are broken down through chemical changes
Common in warm, humid climates
Example: Limestone highly affected by acids
Mechanical
Rocks are broken down through physical changes
Common in harsher climates
Example: water freezing in cracks expands and breaks rock apart

47. WEATHERING SUMMARY
PHYSICAL WEATHERING – INCREASES SURFACE AREA - COLD/HUMID CLIMATE
CHEMICAL WEATHERING – WARM/HUMID CLIMATE
IN BOTH CASES, WATER IS THE PRIMARY INGREDIENT

48. THE END PRODUCTS OF WEATHERING
CALLED SEDIMENTS OR SOIL
SOIL: a combination of sediment, rock minerals, and humus (organic material from biologic activity)