1. Aim: How can we identify the forces that break down rocks?
Weathering
Aim: How can we identify the forces that break down rocks?

2. Do Now: Compare the 2 obelisk pictures.

3. 1. Weathering and Erosion
erosion carries the pieces away.
a. Weathering breaks down rock into sediments
b. Weathering and erosion work together to change Earth’s surface.

4. 2. Weathering:
Physical and chemical processes that break down and change the shape of rock on Earth’s surface.
Physical weathering = mechanical changes
Chemical weathering = chemical changes weaken the rock

5. Physical Change:
Does not produce a new substance
Changes phase or shape
Ex: cutting, melting, freezing
Chemical Change:
New substances are formed
Ex: burning, rusting

6. 3. Physical (mechanical) weathering:
a. The rock is:
broken into smaller pieces
peeled or cracked
edges are worn down
b. The rock is the same type, but changed in size and shape.

7. 4. Types of physical weathering
1. Ice wedging or frost action: Repeated freezing and thawing (melting) of ice/water
2. Plant growth: in cracks of rocks
3. Animal action: digging or burrowing
4. Abrasion: grinding away of rock pieces carried by water, wind, ice, or gravity.
5. Temperature Change: Heating expands rock and Cooling contracts rock

8. Ice wedging – repeated freezing and thawing of ice in cracks of rocks eventually splits the rock.

9. Why does water break apart rocks when it freezes?
Water expands (gets bigger) when it freezes!
Why does ice float?

10. Plant growth – seeds can drop into cracks in rocks and grow…eventually splitting the rock.

11. Abrasion – sharp edges get worn down and smoothed by water

12. Heating/Cooling or freeze/thawing can crack roads

13. Abrasion by wind

14. 5. What does a rock look like that weathered in water?
1. Rocks weathered in water are rounded and smooth.
2. Water causes more weathering and erosion than any other force on earth.

15. 6. What do gravity and glaciers do to rocks?
Abrasion by gravity and glaciers breaks rocks into jagged pieces.

16. Down fell a face The Old Man in the Mountain…. Weathered away!
Of a million years counting
The king of the mountain
And guard of the valley below
The last generation
The very last era
Never to see again
5/3/03
Weathered away!

17. Compare – which is older?

18. Which weathering agents might have changed Cleopatra’s needle?

19. HW Read pgs 40-42 Answer questions 1,2,3, & 5 on pg. 45
What factors cause mechanical weathering?
Describe 3 causes of chemical weathering.
What factors affect the rate of weathering?
Explain what you expect to find after a boulder with many cracks is left for 100 years.