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The Process of Studying Landforms
Several important aspects
Internal Processes: building up landforms
1. Crustal Rearrangement: Earth's dynamic crust and the consequences
2. Vulcanism: origin and movement of molten rock
3. Diastrophism
Next: External processes
McKnight 15.1: Denudation: three processes
Denudation: disintegration, wearing away, and removal of rock material; implies a lowering of earth's surface (via wearing away, not internal processes)
Most of these processes get lumped together as "erosion," but look at them
individually for our discussion.
1. Weathering
"The mechanical disintegration and/or chemical decomposition that destroys the coherence of bedrock and begins to fragment rock masses into progressively smaller components."
Weathering occurs when bedrock is exposed to the atmosphere
1a. A Typology of Cracks and Crevices in Rock
1a1. Microscopic spaces: tiny but allow weathering agents into bedrock
McKnight 15.4 Joints vs Faults
1a2. Joints: stress cracks without movement of the rock on either side of the crack
1a3. Faults: more substantial cracks with movement of the rock on either side of the crack
1a4. Lava vesicles: crevices in lava caused by gases being trapped in cooling lava
1a5. Solution cavities: holes formed in calcareous rocks (limestone) as the soluble minerals
are dissolved and carried away by percolating water
1b. Weathering Agents
The agents that get into the cracks and crevices and continue the process of breakdown
Three principal categories of weathering: mechanical, chemical, biological...
1b1. Mechanical Weathering
Physical disintegration of rock material without any change in its chemical composition
McKnight 15.8: Freeze Thaw action on big rock
McKnight 15.9: Freeze Thaw action on big rock
Salt wedging
Temperature variations and mechanical weathering
Biotic activities: living organisms promote mechanical weathering
McKnight 15.13: Surface Area and Mechanical Weathering
1b2: Chemical Weathering
Decomposition of rock by changes in the chemical composition of its minerals
Mechanical weathering exposes rock to chemical weathering
Common chemical weathering: oxidation
Oxidation: when oxygen dissolved in water comes in contact with rock minerals
WWW) Iron Oxide (rust) on rock
Hydrolysis: chemical union of water and minerals
Carbonation: carbon dioxide (atmosphere) and carbonate rocks
1b3. Biological Weathering
Weathering at interface of the lithosphere and biosphere
McKnight 15.15: Tree Roots
WWW) Lichens
McKnight 15.17: Climate, Biomes, and Weathering
McKnight 15.1: Weathering, Mass Wasting, Erosion
2. Mass Wasting
Mass wasting: process whereby weathered material is moved a relatively short distance downslope under the direct influence of gravity
Angle of repose:the steepest angle that can be assumed by loose fragments on a slope without downslope movement
McKnight 15.18: Mass Wasting
Types of mass wasting vary in speed and relationship to moisture
2a. Fall
McKnight 15.19: talus or scree
2b. Slide
An instantaneous collapse of a slope
Slump: related to a slide
2c. Flow
2d. Creep
Slowest and hardest to see of mass wasting phenomena
Cannot normally see creep
McKnight 15.25: Terracettes
Sum: External Processes
McKnight 15.1: Denudation: three processes
Denudation: disintegration, wearing away, and removal of rock material; implies a lowering of earth's surface
1. Weathering: processes that break up rock at the earth's surface
2. Mass Wasting: processes that move fragmented rock short distances down slope
Next:
3. Erosion
E-mail: jbkrygier@owu.edu
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