2. Weathering, Erosion, and Soil

3. Yosemite Valley, California
Mountains Carved by Glaciers

4. Grand Canyon, Arizona
Carved out by the Colorado River

5. Bryce Canyon, Utah Acidic Rainfall has worn away these rocks.
The harder rocks remain standing… but for how long?

6. Weathering The 2 G’s and the 3 W’s
Process by which rocks are broken down due to exposure to processes occurring at the Earth’s surface
Caused by
Water
Waves
Wind
Gravity
Glaciers
The 2 G’s and the 3 W’s

7. 2 Types of Weathering
A. Mechanical Weathering also called Physical weathering
Rock is broken down into smaller pieces of the same material
(no change in composition)
B. Chemical Weathering
The breakdown or decomposition of rock that occurs when minerals are changed into different substances
(change in composition)

8. Mechanical/Physical Weathering
Frost (Ice) Wedging
Process in which water freezes in the cracks of rock and wedges (pushes) it apart because water expands when it freezes.
Occurs where there are frequent freezes and thaws.

9. Explain what is happening.

10. Frost/Ice Wedging can cause Potholes to form in pavement

11. Mechanical/Physical Weathering
2. Abrasion
The wearing away of rock material by grinding action
Usually caused by sediment in Wind, Water, and Glaciers

12. Wind abrasion- sandblasting effect on stationary rocks as seen here in Arches National Park

13. Hydraulic abrasion- water & sediments flowing over boulders as seen here in Ohiopyle State Park, Pennsylvania
Notice the rounded river rocks

14. Mechanical/Physical Weathering
3. Plants and Animals
Plant roots can split rock
Also known as: “Root pry” or “Root action”
Animals dig holes ,breaks up rocks

15. Tree growing
out of rock,
Shenandoah
National Park
Tree roots also break up sidewalks

16. Mechanical/Physical Weathering
Exfoliation- gradual peeling of layers due to uplift and frost action, typical of granite domes like those in Yosemite N.P.

17. Exfoliation of Igneous rock

18. O2 Chemical Weathering Chemical Weathering
The breakdown or decomposition of rock that occurs when minerals are changed into different substances
(change in composition)
Involves Water ,water vapor, Acids, and/or Oxygen O2

19. Chemical Weathering Hydrolysis
Carbonic Acid in water dissolves Calcite. This chemical weathering can hollow out underground Caverns
Limestone and Dolomite both dissolve because they contain Calcite

20. Acid rain (carbonic acid) weathering the details of statues and tombstones Ex: Marble and Limestone

21. Chemical Weathering Oxidation This is why Mars is the red planet
Oxidation of minerals with iron (magnetite, pyrite) results in the formation of rust or iron oxide.
This is why Mars is the red planet
Copper turns rocks green

22. Rate of Weathering Surface area Rock composition Climate
How fast a rock weathers depends on 3 factors:
Surface area
Rock composition
Climate

23. Rate of Weathering Surface area
The greater the surface area, the faster the weathering rate
There are more surfaces to be weathered

24. Rate of Weathering Rock composition
Some minerals are more resistant than others
For example, quartz is more resistant (harder) than calcite
Quartz
Calcite

25. Rate of Weathering Climate
(long term pattern of moisture and temperature)
Weathering rates are faster in warm, wet climates
Desert vs. Rainforest