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Weathering and Erosion Notes Weathering: Breaking down of rock or soil Mechanical: physically breaking it down Chemical: chemically breaking it down Types of Mechanical Weathering: Plants growing through rocks and breaking them (trees through sidewalks) Rocks growing crystals can split rocks Rapid cooling can cause rocks to weaken and split Rapid heat (like a campfire or forest fire) can cause rocks to expand and break Animals burrowing in rocks When rocks freeze, the water expands and causes rocks to break Water and the sediments it contains flowing through rock Rain pelting rocks Windstorms Sandstorms ****Most mechanical weathering happens in cold and wet climates due to water freezing in rocks and splitting them apart. Types of Chemical Weathering: Weak acids can be formed in water and cause chemical weathering Carbonic acid is produced when CO2 reacts with water and can weather rocks Some chemicals can cause rusting reactions in rocks Acid Rain Animal Waste Pollution ****Since most chemical weathering occurs where there is lots of rain due to weak acids forming in water, most chemical weathering occurs in warm and wet climates where there is lots of rain. The following can indicate that a chemical change took place, although this evidence is not conclusive: Change of color (for example, silver to reddish-brown when iron rusts) Change in temperature or energy, such as the production (exothermic) or loss (endothermic) of heat Change of form (for example, burning paper) Light, heat, or sound is given off Formation of gases, often appearing as bubbles Formation of precipitate (insoluble particles) The decomposition of organic matter (for example, rotting food) Erosion: Moving of sediments produced by weathering Glaciers: A slow moving river of ice that flows downhill carried forward by its huge weight. How glaciers form: When snow remains in one location long enough, it transforms into ice. How glaciers cause erosion: The rocks dragged along underneath it gouge deep into the ground creating U-shaped valleys with steep sides and flat bottoms. Glaciers can also melt and then re-freeze causing rocks to break apart.