1. Ch.12, Sec.1 - Weathering Weathering
- weathering is the breakup of rock due to exposure to processes that occur at Earth’s surface
- mechanical weathering, or disintegration, takes place when rock is split or broken into smaller pieces of the same material without changing its identity
- mechanical weathering is also called “physical weathering”

2. Ch.12, Sec.1 - Weathering
- chemical weathering, or decomposition, takes place when rock’s minerals are changed into different substances
- mechanical & chemical weathering almost always act together

3. Ch.12, Sec.1 - Weathering Mechanical Weathering
- water occupies 10% more space when it freezes, so more pressure is applied to surrounding walls
- when water freezes in the cracks of rocks, it wedges the rock apart
- frost wedging only occurs in areas where the temperature fluctuates above and below freezing point

4. Ch.12, Sec.1 - Weathering
- frost wedging occurs on mountaintops, in porous rocks, and also on our highways (potholes)

5. Ch.12, Sec.1 - Weathering

6. Ch.12, Sec.1 - Weathering

7. Ch.12, Sec.1 - Weathering
- mechanical weathering can also create abrasion, which is the grinding of rocks, pebbles, and boulders against one another
- sand is a product of abrasion as pebbles get ground down into particles of sand as they are carried by rivers, streams, and ocean waves

8. Ch.12, Sec.1 - Weathering
- the growth of plants and the activities of animals also contribute to the mechanical weathering of rock
- the roots of trees, shrubs, & mosses help to split rocks as they grow
- ants, earthworms, rabbits, woodchucks, and other animals dig holes in soil allowing air & water to weather bedrock

9. Ch.12, Sec.1 - Weathering
- the upward expansion of rocks that are formed deep underground may result in a mechanical weathering process called exfoliation
- reduced pressure on the surface of granite can create curved joints that are parallel to the surface – eventually they get exposed and break down over time
Half Dome (exfoliation dome) at Yosemite National Park, California
Yosemite National Park

10. Ch.12, Sec.1 - Weathering

11. Ch.12, Sec.1 - Weathering Stone Mountain (exfoliation dome) in Georgia
Stonewall Jackson, Jefferson Davis, & Robert E. Lee
(Civil War Heroes for the Confederacy)
Stone Mountain (exfoliation dome) in Georgia

12. Ch.12, Sec.1 - Weathering
Sugarloaf Mountain (exfoliation dome) in Brazil
Sugarloaf Mountain in Rio de Janeiro, Brazil

13. Ch.12, Sec.1 - Weathering Chemical Weathering
- chemical weathering occurs almost everywhere because water or water vapor is found almost everywhere
- all chemical weathering involves at least one of the following: water, water vapor, oxygen, and acids
- the chemical weathering by reaction of water with other substances is called hydrolysis

14. Ch.12, Sec.1 - Weathering
- water’s chemical effect on minerals is increased by the presence of acids that are dissolved in the water: carbonic acid & sulfuric acid
- carbonic acid is created from excess carbon dioxide (vehicles) & sulfuric acid is created from sulfur burn-off in manufacturing plants
- these acids mix with rain in the atmosphere and cause acid rain, which further increases chemical weathering

15. Perry’s Cave at Put-in-Bay, Ohio Mammoth Cave in Kentucky
Ch.12, Sec.1 - Weathering
- carbonic acid has a dissolving effect on limestone and can create caverns once it mixes with water and seeps into the ground
Perry’s Cave at Put-in-Bay, Ohio
Mammoth Cave in Kentucky

16. Zion National Park, Springdale, Utah Cathedral Rocks, Sedona, Arizona
Ch.12, Sec.1 - Weathering
- the brown or red color of some exposed rocks may be the result of a process called oxidation
- oxidation is a chemical reaction of oxygen with other substances, especially iron-rich rocks
Zion National Park, Springdale, Utah
Cathedral Rocks, Sedona, Arizona

17. more surface area = faster mechanical/chemical weathering
Ch.12, Sec.1 - Weathering
Rates of Weathering
- under average conditions, weathering is a slow process
- the three factors that increase weathering are: surface area, composition of the rock, and climate
- more surface area exposed to the elements means faster weathering of the rock
more surface area = faster mechanical/chemical weathering

18. McMurdo Dry Valley Desert, Antarctica
Ch.12, Sec.1 - Weathering
- granite, quartz, and marble are not easily weathered, whereas gypsum, feldspar, and limestone weather at faster rates
- warm, wet climates are conducive to faster mechanical/chemical weathering because of the excessive moisture, changes in pressure, and changes in temperature
- cold, dry climates are conducive to faster mechanical weathering because of the excessive winds
McMurdo Dry Valley Desert, Antarctica