Lecture 10 - Weathering - Chapter 15 15.0-15.4 and...

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Chapter 15 15.0-15.4 and 15.7-15.12 and 15.14
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Caraballeda Caraballeda Caracas Caracas Caracas airport Caracas airport Landslide Landslide scars scars Alluvial fan Alluvial fan 15.00.a -How does soil and other loose material form on hillslopes? -What factors determine whether a slope is stable or is prone to downhill movement?
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Weathering - disintegration and decomposition of rock Mechanical weathering – physical breakdown Chemical weathering – chemical reactions Carbonic acid (H 2 CO 3 ), reacts with calcite (CaCO 3 ) and feldspar (SiO 2 ) 4Fe 3 O 4 (Magnetite) + O 2 6Fe 2 O 3 (Hematite) Erosion – Transport of weathered rock particles Water, wind, ice thelenduflo.weebly.com
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Weathering Rock breaks down in place, without moving Erosion Weathered rock particles are picked up and moved by flowing water, wind or glacial ice Weathering and erosion provide the sediment that eventually makes up sedimentary rock (Chapter 6)
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Weathering - disintegration and decomposition of rock at or near the Earth's surface Mechanical Weathering - disintegration Chemical Weathering - decomposition Text 15.1
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Overlying material removed from rock Pressure decreases Rock expands Joints ( cracks) form * exfoliation joints * columnar joints * planar joint sets Text 15.1 Example: Joints
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exfoliation joints : form in plutonic rocks - curved, parallel cracks in the rock, giving the overall appearance of an onion Text 15.1
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Text 15.1
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columnar joints (lava flows) - flow cools lava contracts (like mudcracks) cracks go through as cooling progresses. Devil’s Postpile, California Devil’s Tower, Wyoming Text 15.1
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planar joint sets form in layered rocks -- one set commonly forms parallel to the layering, and two or three sets perpendicular to that plane. Text 15.1
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When joints form. water can seep down into the rock, starting physical and chemical weathering. Text 15.1 www.geography.learnontheinternet.co.uk
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Frost wedging - As water in joints freezes, it expands and pushes against the walls of a joint. This forces the crack tip to grow further into the rock. Text 15.1 After Joints Form…
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Mechanical Weathering Once loose, a block of rock can be moved outward, eventually allowing gravity to pull it down. Text 15.1
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Loose blocks of rock fall from steep or overhanging cliffs (mass wasting) Text 15.1
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Talus slope Text 15.1
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Root wedging -- Tree roots work their way into cracks in rocks, and then grow larger and larger through time. This also wedges rocks apart. Text 15.1 After Jointing…
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Mechanical Weathering Differential Weathering Different rock - different resistance to weathering More resistant layers (lava flows, sandstone) form cliffs Less resistant layers (shale) form slopes Text 15.1
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Chemical Weathering Chemical weathering Water and ions dissolved in water + minerals Change mineralogy and chemical composition Text 15.2
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Three Types: Solution - calcite dissolve in acidic rain water Oxidation - mafic (iron-rich) minerals can rust Hydrolysis – Mineral + water Clay Text 15.2 Chemical Weathering
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