ch.12, sec.1 - weathering weathering weathering - weathering is the breakup of rock due to exposure...
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Ch.12, Sec.1 - WeatheringWeathering
- 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”
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
Ch.12, Sec.1 - WeatheringMechanical 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
Ch.12, Sec.1 - Weathering
- frost wedging occurs on mountaintops, in porous rocks, and also on our highways (potholes)
Ch.12, Sec.1 - Weathering
Ch.12, Sec.1 - Weathering
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
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
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
Ch.12, Sec.1 - Weathering
Ch.12, Sec.1 - Weathering
Stonewall Jackson, Jefferson Davis, & Robert E. Lee(Civil War Heroes for the Confederacy)Stone Mountain (exfoliation dome) in Georgia
Ch.12, Sec.1 - Weathering
Sugarloaf Mountain (exfoliation dome) in Brazil Sugarloaf Mountain in Rio de Janeiro, Brazil
Ch.12, Sec.1 - WeatheringChemical 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
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
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
Mammoth Cave in KentuckyPerry’s Cave at Put-in-Bay, Ohio
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
Ch.12, Sec.1 - WeatheringRates 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
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