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Weathering Notes I. II. III. Weathering A. Weathering is a slow, continuous process that affects all substances exposed to the atmosphere. B. Evidence of weather a. Rust, peeling paint, fading colors, cracks in buildings b. Piles of broken rock at the base of a cliff (talus) Mechanical weathering A. Rocks are broken into different shapes and smaller pieces. B. Examples a. Temperature changes (hot or cold) i. Results in cracks, flakes or exfoliation (sheets) b. Frost action i. Water gets into cracks and freezes, expanding the size of the crack c. Organic activity i. Root pry by growing roots ii. Animal activity d. Gravity i. Falling rocks may break e. Abrasion i. Wearing away material by particles carried by wind, water or ice Chemical weathering A. Changes occur in the mineral composition (chemical) of rocks a. Decomposition i. Minerals are broken down into other substances b. Water i. Most chemical weathering is caused by water ii. Rocks that dissolve are soluable c. Oxidation i. Process in which oxygen combines with another substance ii. Example—rust d. Carbonation i. When carbonic acid (water + soil) reacts with another substance (calcium or limestone) ii. Results can be caves or sinkholes e. Sulfuric acid i. Sulfur dioxide combines with moisture in the air to form an acid ii. Results can be the dissolving of materials iii. Common source is volcanic gases f. Plant acids i. Plant produce acids that may dissolve rocks IV. ii. Root tips produce this acid iii. Lichen produces this acid Rates of weathering A. The rate of weathering depends on 5 factors a. Mineral composition of rocks b. Climate c. Time d. Air pollution e. Amount of exposed surface