1. Forces That Shape Our
Earth:
Weathering
And
Erosion

2. Weathering & Erosion:
 Erosion and weathering are major
forces that shape Earth’s surface.
 For example, the Grand Canyon
was formed through erosion by the
Colorado River running through it!

5. What is weathering?
Weathering: The breaking down
of rocks into smaller pieces.
1. Mechanical /Physical
2. Chemical
Hulk
Rock
Smash!

6. So what is erosion?
Erosion:
The movement
of weathered
rock by wind,
water, glaciers
& gravity

8. Types of Weathering:
Mechanical/Physical:
Rock is physically broken into smaller
pieces (larger pieces become smaller
pieces of the same rock)
Chemical:
Rock is chemically changed (like
rusting or dissolving away)

9. 5 Agents of Mechanical
Weathering:
1. Release of Pressure
2. Freezing & Thawing
3. Animal Actions
4. Plant Growth
5. Abrasion

10. Release of Pressure
 As the surface of a rock is
eroded, the rock begins to release
pressure
 Causes top layers of the rock to
crack and flake off

11. Release of pressure: rock
cracks like an egg shell

12. Freezing & Thawing
When water in the cracks
of rocks freezes it
expands causing the
crack to enlarge or get
bigger. The ice melts &
refreezes over & over,
breaking the rock apart.

13. Result of Freezing & Thawing

14. Animal Actions
Animals dig (burrow) through
the ground to make their
homes. This loosens the soil &
breaks apart rocks.

16. Plant Root Growth
Plants roots can grow into
cracks in the rock, slowly
breaking them apart.

18. Abrasion
 Sand and other rock particles in
wind, water or ice can wear
away exposed rock surfaces.
 Like sandblasting or sandpaper
on wood

21. Chemical Weathering
The process that breaks down
the surface of rock by
chemical changes.

22. 5 Agents of Chemical
Weathering
1. Water
2. Oxygen
3. Carbon Dioxide
4. Living Organisms
5. Acid Rain

23. Water
Water dissolves rock
Water is the most important
cause of chemical weathering

25. Oxygen
 Oxygen + Water + Iron = Rust
through the Chemical reaction
called Oxidation
 Rock will become crumbly, soft,
and appear reddish-brown in color

26. Rusted rock on hillside

27. Carbon Dioxide
CO2 + rainwater = Carbonic Acid
Carbonic Acid weathers softer rock
like limestone & marble as it seeps
into spaces in rock.
Ex: sinkholes, caves

29. Living Organisms
The roots of plants make a
weak acid that slowly
dissolves rocks around the
plant.

30. Lichens grow on rock

31. Acid Rain
Acid rain causes rocks to
weather very rapidly.