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Weathering • Weathering- the breaking down of rock due to physical and chemical changes at the earth’s surface. 2 types: • Physical Weathering- the breaking of rocks into smaller particles. • Chemical Weathering- the changing of minerals into new substances. Typical ways of breaking rocks • Frost Action • Plant roots • Animal burrows • Abrasion Physical Weathering Frost Action- this occurs when liquid water seeps into cracks in rock and freezes. It expands as it becomes ice and tends to widen the crack. Over time this can break up the rock. Plant Roots- As a plant grows it sends roots into cracks in rocks. The roots push against the cracks and eventually push the rock apart. Bare rock is eventually covered with soil by weathering & Organic Succession O- Live Organics A- Organic Rich B- Leeched Zone C- Sediments SoilMixture of sediment and Humus HumusDecaying organic matter Soil HorizonsA- Organic Rich B- Leeched Zone C- Sediments D- Bedrock Residual Soil – Soil that was derived from the underlying bedrock. Transported SoilsEroded sediments that have been deposited Soil DepletionRemoving nutrients from the soil by either erosion or pollution Methods of Soil Depletion Over Farming Erosion Salinization Soil DepletionRemoving nutrients from the soil by either erosion or pollution Methods of Soil Depletion Over Farming Erosion Salinization Methods for Soil Conservation Rotational Crop Farming Strip Farming Soil DepletionRemoving nutrients from the soil by either erosion or pollution Methods of Soil Depletion Over Farming Erosion Salinization Methods for Soil Conservation Rotational Crop Farming Strip Farming Terracing Wind Breaks Desalinization of irrigation water Soil DepletionRemoving nutrients from the soil by either erosion or pollution Methods of Soil Depletion Over Farming Erosion Salinization Methods for Soil Conservation Rotational Crop Farming Strip Farming Terracing Wind Breaks Desalinization of irrigation water Soil DepletionRemoving nutrients from the soil by either erosion or pollution Methods of Soil Depletion Over Farming Erosion Salinization Methods for Soil Conservation Rotational Crop Farming Strip Farming Terracing Wind Breaks Desalinization of irrigation water (remove salts) • Abrasion- As rocks are carried by a stream they smash into one another and are broken apart. Other agents of abrasion: • Wind • Moving ice • Gravity Resistance to weathering • Some minerals are harder than others. • Quartz and feldspar are very hard and resist physical weathering. • Softer minerals like mica are quickly broken apart at the surface. Surface Area and Weathering • Breaking the rock into smaller pieces increases the surface area. • The more surface area, the faster the rock weathers. Chemical Weathering •Rocks can also be broken down by a chemical change. •Chemical change breaks down the rocks to form a different substance. •Example: Rain mixes with CO2 and forms carbonic acid. This chemically reacts with CaCO3 (calcite)and causes it to dissolve in water. •The water then carries the material away and a cavern is left behind. •If the overlying rock is not supported it will collapse forming a sink hole Although chemical weathering is accelerated by heat and moisture it also occurs slowly in arid regions. Example: Iron bearing rocks and minerals are broken down by oxidation. This process is accelerated in the presence of water. Iron Oxide is formed. Review: Chemical Weathering is accelerated by____________ Abrasion is caused by________ A rock that weathers slower than another is said to be_________ ___ __________ http://www.youtube.com/watch?v=Xtk_bqkfeyE&list=PL2E5EA2EBAE6A463D&safe=active http://www.youtube.com/watch?v=iZDJCxa_qis&safe=active http://www.youtube.com/watch?v=0Va7E7KOz94&safe=active http://www.youtube.com/watch?v=K1qY8nPqcCw&safe=active
