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The Process of Studying Landforms

• 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
   
2. Vulcanism: origin and movement of molten rock
   
3. Diastrophism: deformation of solid rock in the Earth's crust due to pressure from below

External Processes: breaking down landforms: forces in atmosphere + hydrosphere

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
   
   • cracks and crevices in rocks: microscopic, faults, joints
     
   • weathering agents: mechanical, chemical, biological

2. Mass Wasting: processes that move fragmented rock relatively short distances down slope: falls, slides, slumps, flows, and creep

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

McKnight 9.5: The Hydro Cycle

Weathering and mass wasting enhanced by presence of water: hydro cycle

But erosion is fundamentally the result of the presence of water

Fluvial Processes: any environmental processes involving the flow of water

• overland flow: un-channeled down-slope movement of surface water

• stream flow: channeled movement of water along a valley bottom

• More: Geology 275: Hydrogeology

1. Impact of Fluvial Processes on the Landscape

McKnight 16.1: Fluvial Process Photo

• flowing water has huge effect on shaping landforms

• theories of landform development are based on fluvial processes

1a. Traditional Theory of Landform Development: The Geomorphic Cycle

• William Morris Davis: around 1900

McKnight 16.35a, b, c, d: Davisian Geomorphic Cycle

• evolutionary theory: the life-cycle for landscape: like an organism

• initial surface:

  
  
  
  

• youth:

  
  
  
  

• maturity:

  
  
  
  

• old age:

  
  
  
  

• peneplain: flat, featureless landscape with minimal relief

  
  
  

• rejuvenation:

1b. Critique of Davisian Cycle Theory: Crustal Change and Slope Development

• various ways in which Davis's theory did not work

  
  
  
  McKnight 16.36: Slope Retreat: Penck

  • slopes retreat, retaining their angle of slope

  • rather than wear down (lessening angle) a la Davis

  
  Further problem: both Davis and Penck assumed uniformity of bedrock and tectonics

Much variation in bedrock, regolith, soil around the earth: some soft, some hard

Crustal movement (vertical, horizontal) also varies: excessive uplift, minimal uplift

• development of dynamic crust theory after Davis and Penck

McKnight 16.37: Dynamic Equilibrium

Simultaneous uplift (internal forces) and denudation (external forces, primarily water)

Dynamic equilibrium rather than evolution

• problems:

Both Davisian evolution and Dynamic Equilibrium theories explain some landforms

Key: geographic variations (where) in bedrock and tectonic activity vital to understand

2. Fundamental Definitions and Concepts of Fluvial Processes

McKnight 16.2: Valleys and Interfluves

2a. Valleys and Interfluves

• valley:

  
  
  

• interfluves:

2b. Drainage Basins - Watersheds

• watershed:

  
  
  

• drainage divide:

2c. Erosion

Weathering >> Mass wasting >>

• erosion: moves soil and regolith substantial distances from original location

• deposition: when soil and regolith moved by erosional forces is set back down
  WWW) Grand Canyon

Two basic types of erosion: by overland flow and steam flow

Erosion by Overland Flow

Beginnings of erosion: on interfluves

McKnight 16.5: Splash erosion

• splash erosion:

• sheet erosion:

• rill erosion:

• gully erosion:

Erosion by Streamflow

Channeled flowing water has more ability to erode material

• dislodge

• undercut

• abrasion

Erosive effectiveness

• speed and turbulence of the flow:

• resistance of bedrock:

2d. Transportation: of rock particles via overland or streamflow

McKnight 16.7: Transport of particles

stream load: material carried by stream flow: three components

1. dissolved load:

2. suspended load:
   • majority of stream load

3. bedload:
   • saltation:

   • traction:

   • bedload least amount of stream load

Any stream varies in the amount of material it can transport:

Competence: measure of the particle size a stream can transport, expressed by the diameter of the largest particle that can be moved; varies with flow speed and amount

Capacity: measure of the amount of solid material a stream has the potential to transport, expressed as the volume of material passing a given point in the stream channel during a given time interval

2e. Deposition

Alluvium:

Changes in gradient, channel widening, or change in direction

• deposits at canyon mouths, floodplains, river-bends

Most material deposited in sitting bodies of water: lakes, oceans

• more on all these later...

3. Stream Channels

Reiterate: fluvial processes: those that involve running water

• overland flow: unchanneled down-slope movement of surface water

• stream flow: channeled movement of water along a valley bottom

Overland flow relatively simple

Streamflow more complicated: four characteristics of individual streams and rivers

3a. Structural Relationships

The course of a stream channel is guided and shaped by the nature and arrangement of the underlying bedrock

McKnight 16.15: Dendritic Drainage Pattern

• most common: little or no influence of underlying bedrock (eg., in regolith, soil)

McKnight 16.16: Trellis Drainage Pattern

• folded strata: ridge and valley landforms

McKnight 16.17: Trellis and Dendritic Drainage Patterns

• both in W. Virginia

McKnight 16.18: Radial Drainage Pattern

• shaped by isolated mountain (usually a volcano)

McKnight 16.19: Centripetal Drainage Pattern

• inverse of Radial: convergence on a central basin

3b. Channel Flow

McKnight 16.9: Friction and Streamflow

• friction: where?

3c. Turbulence

• turbulence:

3d. Channel Changes

McKnight 16.11: Straight and Meandering channels

Straight: uncommon and usually caused by underlying geologic structure

• thalweg:

McKnight 16.12: Meandering Stream

Meandering: serpentine pattern

softer underlying material, on flat land
dynamic:
oxbow lakes

McKnight 16.13: Braided channel

interwoven and interconnected shallow channels w/islands
moist areas, marshy

4. Stream Systems

• Stream Channels: characteristics of individual streams and rivers

• Stream Systems: how streams and rivers relate to each other

4a. Drainage Basins

McKnight 16.3: Drainage Basins

• hierarchy of drainage basins

McKnight 16.4: Stream Order

• hierarchy of streams in any drainage basin

4c. Permanence of Flow

Perennial streams: permanent, year round flow

• where

Intermittent (ephemeral) stream: flow only part of the year

• where/when

5. Shaping and Reshaping of Valleys by Fluvial Processes

Horizontal and vertical reshaping of valleys

• deepening: largely erosion

• widening: weathering, mass wasting, erosion

• lengthening: due to deposition

• other depositional features

• and rejuvenation: when land's surface is uplifted by internal forces

5a. Valley Deepening

McKnight 16.21: Base Level

Limits to deepening (vertical erosion): base level

• exceptions:

• local base levels:

Deepening caused by hydraulic power of flowing water, prying and lifting by moving water, abrasion

Deepening most effective in upper reaches of streams: steepest slopes

McKnight 16.22: Knickpoints

• collective term for waterfalls and rapids

• where occur:

• why:

McKnight 16.B: Niagara Falls

• undermining leads to break up of resistant material: falls migrate upstream

5b. Valley Widening

• weathering and mass wasting lead to valley widening

• also stream flow: lateral erosion

• more effective with lesser streambed gradients, flatter areas

McKnight 16.23: Meanders and Lateral Erosion

• patterns of erosion and deposition

McKnight 16.24: Valley Widening

• the floodplain

5c. Valley Lengthening

McKnight 16.25: Headward Erosion

Headward Erosion: key location

• what is it

  
  
  

• McKnight 16.26: Headward Erosion Image

Delta Formation: also lengthens valleys

how

5d. Deposition in Valleys

While valleys are deepened, widened, and lengthened over time deposition of sediments does occur

McKnight 16.29: Flood plain

• much deposition due to floods and resultant floodplains

McKnight 16.31: Natural Levees

Floodplain slightly higher along edges of stream channel

• why and how

• backswamps:

• yazoo stream:

5e. Steam Rejuvenation

McKnight 16.33

• When internal processes and external processes meet

• tectonic uplift: isostacy

McKnight 16.34: Entrenched Meanders

• how it happens

Sum: Fluvial Processes: any environmental processes involving the flow of water

• overland flow: unchanneled down-slope movement of surface water
  
• stream flow: channeled movement of water along a valley bottom

1. Impact of Fluvial Processes on the Landscape

• effects great: major theories of landform development based on fluvial processes
  1a. Traditional Theory of Landform Development: The Geomorphic Cycle
  
  1b. Critique of Davisian Theory: Crustal Change and Slope Development
  
  1c. Equilibrium Theory

2. Fundamental Definitions and Concepts of Fluvial Processes

2a. Valleys and Interfluves

2b. Drainage Basins - Watersheds - Drainage Divides

2c. Erosion: by overland flow vs. streamflow

2d. Transportation: of rock particles via overland or streamflow

2e. Deposition: of alluvium

3. Stream Channels: Key Characteristics of individual streams and rivers

3a. Structural Relationships: relation to bedrock

3b. Channel Flow: friction

3c. Turbulence

3d. Channel Changes: depth, straight, meandering, braided

4. Stream Systems: how streams and rivers relate to each other

4a. Drainage Basins: hierarchy

4b. Stream Orders: first, second, third,...

4c. Permanence of Flow: perennial vs intermittent

5. Shaping and Reshaping of Valleys by Fluvial Processes

• deepening, widening, lengthening, depositional, rejuvenation

E-mail: jbkrygier@owu.edu

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