1. Lab: What effect does increased surface area on weathering?
Topic: Weathering
DN: Water is a major agent of chemical weathering because water
cools the surrounding when it evaporates;
dissolves many minerals that make up rocks;
has a density of 1g/cm3;
has the highest specific heat of all common Earth materials.

2. What causes the Earth to wear down?
1. PHYSICAL/ MECHANICAL WEATHERING – rocks are broken apart increasing the surface area.
ROCK BEFORE WEATHERING =
ROCK AFTER WEATHERING (just smaller)

3. What causes the Earth to wear down?
2. CHEMICAL WEATHERING – Chemical reactions CHANGE minerals.
ROCK BEFORE WEATHERING ≠ ROCK AFTER WEATHERING

4. What are agents of Mechanical Weathering?
Frost action
Wave action
Growth of plants
abrasion
Actions of animals
Temperature changes
What factors are involved in mechanical weathering?
Changes in temperature and pressure.

5. PHYSICAL WEATHERING FROST ACTION – FROST WEDGING
MOST IMPORTANT IN OUR CLIMATE (effect of temperature)
FROST ACTION – FROST WEDGING
ALTERNATE FREEZE AND THAW
Water expands when frozen

6. ROCKS ARE CRACKED BY WATER FREEZING

7. EXAMPLES: POT HOLES AND FROST HEAVES

9. PHYSICAL WEATHERING – ROOT ACTION (effect of pressure)
PLANT ROOTS UPLIFT AND FRACTURE ROCK

10. Wave Action
Waves pounding against rocks - sand and rocks in the waves help to break up the shoreline.

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

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

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

14. Stream abrasion
‘cutting tools’ of the stream which ‘downcut’ the stream’s V-shaped channel as they roll along.

15. Exfoliation: As pressure decreases the outer layers of rock are stripped away.

16. Actions of animals loosen and break apart rocks in soil

17. How does the hardness of a rock relate to the rate of weathering?
Rate of physical weathering
depends on the resistance (hardness) of the rock and on the kind of climate.

18. Chemical Weathering
The process that breaks down rock through chemical changes.
1) Changes kind of material (ex. iron into iron oxide - rust)
2) Surface phenomenon - reactions occur on the surface of rocks, not inside them (usually).
3) Like most chemical reactions, water is required.
4) Hotter = faster
5) Fastest chemical weathering occurs in warm/moist climates

19. Agents of chemical weathering
Water
Oxygen
Carbon dioxide
Living organisms
Acid rain

20. Water
hydration - minerals in rocks combine with water.

21. Chemical Weathering: Rust
What items have you seen rust?
What can you do to prevent or reduce rusting?

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

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

24. CARBONATION
Stalagmites and stalactites

26. Living Organisms
Plant-like organisms produce weak acids that slowly dissolve rock.

27. Acid Rain
Compounds from burning coal, oil and gas react chemically with water forming acids.

28. Activity: What effect does increased surface area have on weathering?