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The Process of Studying Landforms

Several important aspects

• Knowing Where particular landforms are

• Knowing What the characteristics of the landforms are

• Knowing Why the landform came to be: internal and external processes

Internal Processes: building up landforms

1. Crustal Rearrangement: Earth's dynamic crust and the consequences

• plasticity, isostacy, continental drift, plate tectonics

2. Vulcanism: origin and movement of molten rock

• Volcanic Processes: Extrusive Vulcanism: Surface volcanic landforms
  
• Plutonic Processes: Intrusive Vulcanism: Sub-surface volcanic forms

3. Diastrophism

• deformation of solid rock in the Earth's crust due to pressure from below
  
• some due to continental plate movement some to vulcanism

• Folding: solid rock gets bent
  
• Faulting: crustal stresses also lead to rock being broken

Next: External processes

• operate from the earth's surface or above

• forces in atmosphere + hydrosphere: break down landforms built up by internal forces

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)

1. Weathering: processes that break up rock at the earth's surface

2. Mass Wasting: processes that move fragmented rock relatively short distances down slope

3. Erosion:
   processes that move fragmented rock relatively long distances

Most of these processes get lumped together as "erosion," but look at them individually for our discussion.

WWW) Grand Canyon

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

• characteristics

1a. A Typology of Cracks and Crevices in Rock

1a1. Microscopic spaces: tiny but allow weathering agents into bedrock

• characteristics

McKnight 15.4 Joints vs Faults

1a2. Joints: stress cracks without movement of the rock on either side of the crack

• characteristics

  
  
  
  
  

• McKnight 15.5: joint systems

• McKnight 15.6: master joints

1a3. Faults: more substantial cracks with movement of the rock on either side of the crack

• characteristics

1a4. Lava vesicles: crevices in lava caused by gases being trapped in cooling lava

• characteristics

1a5. Solution cavities: holes formed in calcareous rocks (limestone) as the soluble minerals are dissolved and carried away by percolating water

• characteristics

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

• how it works

McKnight 15.9: Freeze Thaw action on big rock

• where it happens

Salt wedging

• characteristics and how it works

Temperature variations and mechanical weathering

• characteristics and how it works

Biotic activities: living organisms promote mechanical weathering

• characteristics and how it works

McKnight 15.13: Surface Area and Mechanical Weathering

• Intensification of break up: as mechanical weathering increases

1b2: Chemical Weathering

Decomposition of rock by changes in the chemical composition of its minerals

Mechanical weathering exposes rock to chemical weathering

• Moisture vital: why?

  
  
  
  

• Temperature vital: why?

  
  
  
  

• Where chemical weathering occurs

Common chemical weathering: oxidation

Oxidation: when oxygen dissolved in water comes in contact with rock minerals

• what happens

WWW) Iron Oxide (rust) on rock

• why it helps break down of 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

• Algae and fungi living together; draw minerals from rock; and can weaken it

McKnight 15.17: Climate, Biomes, and Weathering

• relationship between temperature, precipitation, and depth of 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

• gravity important here: why, and why variations in slope matter

Angle of repose:the steepest angle that can be assumed by loose fragments on a slope without downslope movement

• effect of water

McKnight 15.18: Mass Wasting

Types of mass wasting vary in speed and relationship to moisture

2a. Fall

• Weathering loosens rock and it tumbles down a slope

McKnight 15.19: talus or scree

• what it is, how it works

2b. Slide

An instantaneous collapse of a slope

• characteristics

Slump: related to a slide

• characteristics; why different from slide or flow

2c. Flow

• part of a slope gently slips downhill

2d. Creep

Slowest and hardest to see of mass wasting phenomena

• speed

• Very slow downhill movement of soil and regolith

• Usually involves the entire slope

• Water is an important factor (speeds up creep)

• McKnight 15.23: Freeze Thaw and Creep

Cannot normally see creep

• but can see its effect on objects on a slope

  
  
  

• McKnight 15.24: Visual Evidence of Soil Creep

• McKnight 15.18: also trees

McKnight 15.25: Terracettes

• terracettes: complicated sets of faint terraces or trails

Sum: External Processes

• operate from the earth's surface or above

• forces in atmosphere + hydrosphere: break down landforms built up by internal forces

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

1a. A Typology of Cracks and Crevices in Rock: microscopic spaces, joints, faults, lava vesicles, solution cavities

1b. Weathering Agents: mechanical, chemical, biological

2. Mass Wasting: processes that move fragmented rock short distances down slope

• fall, slide, slump, flow, creep

Next:

3. Erosion

• processes that move fragmented rock relatively long distances

• Fluvial Processes: any environmental phenomena involving the flowing of water

E-mail: jbkrygier@owu.edu

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