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Weathering Weathering is the process that produces change in the surface of rocks exposed to the atmosphere and/or hydrosphere. Two Categories Of Weathering: Mechanical Chemical weathering weathering is the is where the rock breakdown of rock material is changed into smaller bits and into another pieces without a substance by reacting change in its chemical with a chemical. makeup. ex: hitting, scratching, cracking Frost action (ice wedging)- 1. Water seeps into small cracks in rocks. 2.When the water freezes it expands creating great pressure. 3. The crack widens and allows water to seep deeper into the rock. Plant action- 1. Tiny root hairs seek out small cracks and pits in rock. 2.Once the root hairs find a place they grow and expand. 3.The expansion causes great pressure and cracks the rock. Exfoliation 1. 2. 3. Rocks formed deep in the Earth are made under high pressure. When the pressure is released the rocks expand & crack. May also be caused by alternate heating and cooling of rocks by weather conditions. Abrasion- grinding away of rock by water, wind, ice, or rubbing other rocks. Wetting and Drying When earth gets wet it expands As it dries it cracks OxidationOxygen in the atmosphere chemically reacts with minerals. ex.: rusting of a nail Water (hydrolysis) Minerals are dissolved in water. ex.: Halite, calcite Acid- Carbonic acid: C02 dissolves in rain water forming a weak acid. ex. stalactites and stalagmites Acid Rain: Sulfur Dioxide in the atmosphere dissolves in rain water forming a strong acid (sulfuric acid). Time For a Investigation One student has a bowl with a rock and small croutons in it. Another student has a bowl with a rock and a large crouton in it. Both students will aggressively shake their bowls. Which crouton will experience the most weathering? Rates of Weathering will depend on: Surface area exposed - weathering occurs on the surface. More surface exposed, the faster the weathering will occur. A full, solid block has the least surface area. The interior is safe from exposure. A smashed piece has greatest surface area exposed. The interior can now be attacked. Rates of Weathering will depend on: Mineral composition- some minerals are more resistant than others. –ex.:Quartz is resistant to chemical and physical weathering. Rates of Weathering will depend on: Climatic Conditions: Cold and/or dry climates favor physical weathering. Warm and wet climates favor chemical weathering. Frost action works best in areas where the temperature fluctuates wildly. LET’S SEE IF YOU CAN FIGURE THIS OUT???? Where is the rock more resistant to weathering? Where is the rock least resistant to weathering? You might also see it like this… You might also see it like this…