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Weathering. Weathering and Erosion. Weathering is the chemical or physical breakdown of a rock or mineral due to exposure to the atmosphere . Erosion is the removal or transport of material by 5 possible agents: running water, glaciers, waves, wind, and gravity.
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Weathering and Erosion • Weathering is the chemical or physicalbreakdown of a rock or mineral due to exposure to the atmosphere. • Erosion is the removalor transport of material by 5 possible agents: running water, glaciers, waves, wind, and gravity. • Humans and animals may also play a part in erosion.
Types of Weathering • There are two major types of weathering: • 1. Mechanical (physical) – breakdown of rock or mineral. Just breaks it into smaller pieces, composition of the material is NOT changed!! • 2. Chemical – changes the composition of material as it breaks down.
Physical (Mechanical) Weathering • Some ways physical weathering can occur: • 1. Freezing and thawing of moisture in rockopenings causing rock disintegration. (Water expands as it freezes, this breaks the rock into pieces. Occurs A LOT in our state – causes most potholes!!!) Frost Wedging animation
2. Erosion of upper rock causes underlying rock to expand resulting in cracking and peeling of rock in slabs. • Think of onion skin layers and peeling them off!!
3. Organic Activity – plant roots or animals like burrowing worms can cause rock to breakdown.
4. Wetting and Drying - addition of water to mineral structure causes structure to expand.
Chemical Weathering • There are also several different types of chemical weathering: • 1. Hydrolosis – chemical reaction between waterand other substances. (feldspar weathered into clay by hydrolosis)
2. Carbonic Acid – dissolving of substances by acids in water often leaving insoluble remains.
3. Oxidation – chemical reaction of a substance with oxygen causing arust or patina to form.
Weathering and Climate • Climate plays a very important role in weathering. • The temperature and amount of moisture influences the type of weathering that will occur. • Warm and wet climates produce mostly chemical weathering. • Cool and slightly wet climates produce mostly physical weathering.
Cleopatra’s Needle in Egypt – warm dry climate – little to no weathering occurs Cleopatra’s Needle was moved to New York and has weathered considerably in only 80 years due to the cold and wet climate.
Weathering and Resistance • The harderthe rock or mineral is, the moreresistant it will be to weathering. • Any rock with quartz will be quite resistant due to quartz’s hardness. • What is quartz’s hardness? • Rocks made mostly ofcalcite, a very soft mineral, will be easily weathered. • What is calcite’s hardness?
Porosity and Permeability • Porosity: The percentage of pore space in a material • Permeability: The ability of a material to let liquid (water) pass through it. • Impermeable:When something will not let liquids pass through it(usuallywateris the liquid).
Permeability • If something has Low Porosity, then permeability will be SLOW • If something has High Porosity, then permeability will be FAST