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© 2014 Pearson Education, Inc.
Chapter 2 Lecture McKnight's Physical
Geography
Chapter 15Preliminaries to Erosion:
Weathering andMass Wasting
Modified by AJ Allred for Geography 1000
Salt Lake Community College
© 2014 Pearson Education, Inc.
Original by Andrew MercerMississippi State University
© 2014 Pearson Education, Inc.
Learning Goals of Chapter 15• Define denudation, weathering, mass wasting, and
erosion.
• Differentiate between mechanical, chemical, and biotic weathering.
• Explain frost wedging, salt wedging, temperature changes, exfoliation, angle of repose, and oxidation.
• Identify mass wasting, glaciation, landslide, slump, earthflow, mudflow, creep and solifluction.
© 2014 Pearson Education, Inc.
The sun uses water & gravity to wear down landforms
– Weathering
– Mass wasting
– Erosion
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Weathering and Rock Openings
Notice how water gradually opens joints by gravity flow, freeze/expansion and chemically dissolving rocks.
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More examples of weathering into joints
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Weathering Agents
• Oxygen, carbon dioxide, and water
• Temperature changes – freeze/thaw, expand/contract
• Water penetration in bedrock openings
• Biotic agents – Burrowing and/or plant roots
– Chemical alteration
• Three principal categories– Mechanical
– Chemical
– Biotic
© 2014 Pearson Education, Inc.
Weathering Agents
• Mechanical Weathering– Physical disintegration of rock without changes to its
chemical composition
• Frost wedging– Freeze–thaw action of water
– Ice wedges downward in openings
– Ice melts and water falls farther into larger opening
– Process repeats
– Frost shattering
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Weathering Agents
• Salt wedging– Salt left behind from evaporated water collects and pries
apart rock openings
• Temperature changes– Diurnal and seasonal temperature fluctuations modify
volumes slightly
– Fracturing of rock over long time scales
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Weathering Agents
• Exfoliation– Curved layers peel off of bedrock
– Exfoliation dome
– Unloading through erosion
– Hydration
• Other mechanical weathering processes– Chemical and
biotic impacts on mechanical weathering
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Biological Weathering Agents
– Plant roots break apart rocks, and may also hold soils together.
– Burrowing animals promote water entry and chemical change to soil and rock
– Lichens slowly consumes rock, turning it into soil and dust.
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Mass Wasting
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Mass Wasting
• Fall– Rockfall
– Talus/Scree
– Uniform accumulation of rockfall material – talus apron
– Material tends to collect in cone shaped heaps – talus cones
– Talus cones grow up the mountain
– Slow talus flow in glaciers – rock glaciers
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Slumping – semi-wet material
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Very wet soil can flow
© 2014 Pearson Education, Inc.
Slow Creep
Walls, poles, head stones and other structures slowly move downhill over many years.
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