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Physical Weathering - Environmental Geology - Lecture Slides, Slides of Earth Sciences

In these Lecture Slides, the Lecturer covered the following basic concepts of Environmental Geology : Physical Weathering, Unusual Behavior, Important Property, Wedge, Freezes and Expands, Shatters the Rock, Repeats the Process, Temperatures, Adequate Moisture, Presence of Pathways

Typology: Slides

2012/2013

Uploaded on 07/23/2013

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Physical Weathering
Frost wedging (or freeze-thaw)
Works because water expands when it freezes
This is unusual behavior
Very important property
Water acts as a wedge
Works its way into cracks in the rocks
Freezes and expands
•Shat
ters the rock
Repeats the process as temperatures rise and fall
Frost wedging works best
Adequate moisture
Presence of pathways into the rocks
Cycling of temperatures above and below freezing
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Physical Weathering

Frost wedging (or freeze-thaw)

  • Works because water expands when it freezes
    • This is unusual behavior • Very important property
      • Water acts as a wedge
        • Works its way into cracks in the rocks • Freezes and expands • Shat t ers the rock - Repeats the process as temperatures rise and fall - Frost wedging works best - Adequate moisture • Presence of pathways into the rocks • Cycling of temperatures above and below freezing

Frost Wedging

Skinner, Brian J. and Porter, Stephen C., 2000, The Dynamic Earth: An Introduction to Physical Geology , 4 th^ edition., p. 124.

Mechanical Weathering

Crystal Growth

  • As water evaporates crystals grow – Crystal growth generates huge forces which can shatter rocks

Root wedging

  • Roots of plants work their way into cracks in rocks – Root growth splits rock – Plant acids attach rock (chemical)

Mechanical Weathering—Root Wedging

Physical Weathering

Fire or Heat Spelling

  • Rocks are poor conductors – Intense heating from fire heat only a thin outer shell which spalls away from the rock

Hiker erosion

  • Footsteps over the same area repeatedly wears away surface material

Heat Spalling at Yellowstone

Skinner, Brian J. andPorter, Stephen C.,2000, The Dynamic Earth: An Introductionto Physical Geology , 4 th edition., p. 124.

Effect of Grain Size

Skinner, Brian J. and Porter, Stephen C., 2000, The Dynamic Earth: An Introduction to Physical Geology , 4 th^ edition., p. 131.

Chemical Weathering Factors

Climate

  • Temperature—Warm favors chemical weathering – Moisture—Wet favors chemical weathering – Rates are fastest in the tropics – Rates are intermediate in temperate climates like our own - Rates are slow in arctic or dry climates where mechanical weathering predominates