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Transcript
Weathering and Erosion Soil formation Standards • • • • • • S6E5, S6CS2, S6CS3, S6CS4, S6CS5, S6CS6 S6E3, S6E5, S6CS2, S6CS3, S6CS4, S6CS6, S6CS10 Weathering • 2 types –Mechanical –Chemical Effects of rock type • Hardness of rock determines weathering rate • Chemicals in air – air pollution • Amount of water in air • Temperature of area Mechanical Weathering • When rocks are broken apart by physical processes • Chemical makeup of rock stays the same • Pressure release –Under Earth’s surface –Rock layers break apart –Exfoliation • Layers slowly break off Plants and animals • Water and nutrients collect in cracks and soil • Plants grow in cracks • Animals burrow and leave tunnels and holes in ground Ice wedging • Water enters cracks in rock and freeze. • Expanding water causes rock to break apart • Ice melts and processes repeat. • Abrasion –Wearing down by friction –Moving water (river) –Rocks hitting each other –Ocean waves Chemical weathering • Chemical reactions dissolve the minerals in rocks or change them into different minerals • Weakens rock • Dissolving –Water + carbon dioxide –Dissolves rock into new substance • Rusting –Iron in soil –Oxygen rusts iron –Soil is red in color Natural Acids • Water mixes with carbon dioxide gas and form carbonic acid • Roots and decaying plants give off acids • Dissolve minerals in rock Effects of Climate • Pattern of weather that occur in a particular area over a period of time • Cold areas – mechanical weathering – ice wedging • Warm areas – chemical weathering – rain Surface area • Small pieces of rock have more surface area exposed than large rock • Allows more rock to be exposed and weathering to occur 4.2 Weathering and organic soil formation 1. 2. 3. 4. 5. Climate Slope of land Type of rock Type of vegetation Amount of time rock has been weathering Composition of Soil • • • • • • • Rock sediment Minerals Organic plant matter Decayed animals Microorganisms – bacteria Humus – decayed organisms water Soil horizons • Horizon A – top layer of soil – litter of leaves twigs and other organic material – litter prevents erosion – topsoil – dark and fertile • Horizon B – below A – lighter in color – no litter – less fertile – leaching – removal of dissolved minerals – move from A to B • Horizon C - bottom layer – thickest layer- not much organic matter-not fertile – many rocks Soil types • Type of soil determined – Climate – Region – Rainfall – Types of rock Observable properties of soil • • • • Texture Color Pore space Chemistry Human activities affect soil Land-use • Farming – Overgrazing of animals=desertification – Adding nutrients (organic or artificial) – Top soil erosion – Clear trees – Wind Construction and development • • • • • Roads Houses Malls Stores What are some problems with this? Mining • How would this affect an area? Protection of soil • Crop-rotation • Conservation tillage • Terraces • Contour plowing • Windbreaks Contour plowing Crop-rotation Windbreaks Preventing Soil Erosion • Managing crops • Plant shelter belts – protect soil from wind • Proper grazing management – arid areas farmers do not plow under vegetation – allow grazing of natural vegetation • “No-till” farming – – stalks are left as ground cover during the winter. – Farmers seed area without plowing. – Leftover stalks stop erosion, keep moisture in ground and control weeds. Reduce erosion at construction sites • Cover cleared areas with mulch, mats, or plastic coverings • Water sprayed onto cleared area • New topsoil is added to exposed areas • Area is seeded and reinforced with netting or straws • Retaining walls are built for steeper areas – made of stone, concrete or wood