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51 Cards in this Set

  • Front
  • Back

How are rivers able to sculpt landscapes?

Through...



  1. Erosion
  2. Transportation
  3. Deposition

Define: Erosion

Physically picking up sediment.

Define: Transportation

Moving the sediment.

Define: Deposition

The settling of transported materials.

What does river velocity indicate?

River energy.



  • The speed of the water - determined by the amount of friction on the bank and bed.
  • Deeper rivers flow faster.

What may river energy be used for?


  • Erode the bed and banks.
  • Transport eroded material.

What type of energy do rivers have?

Kinetic Energy 
Evaporation provides rivers with potential energy
Measured as mass times acceleration.
Due to gravity times height above base level.

Kinetic Energy


  • Evaporation provides rivers with potential energy
  • Measured as mass times acceleration.
  • Due to gravity times height above base level.



Where do rivers ultimately derive their energy from?

  • The Sun

Note: Hydrologic Cycle




  • Energy is neither created nor destroyed

Note: First law of thermodynamics

Why changes in height above base level can occur:



Method 1/2


  • Define: Eustatic sea level changes.

Eustatic change is when the sea level changes due to an alteration in the volume of water in the oceans or, alternatively, a change in the shape of an ocean basin and hence a change in the amount of water the sea can hold. Eustatic change is alway...

Eustatic change is when the sea level changes due to an alteration in the volume of water in the oceans or, alternatively, a change in the shape of an ocean basin and hence a change in the amount of water the sea can hold. Eustatic change is always a global effect.



Why changes in height above base level can occur:



Method 2/2


  • Define: Isostatic sea level changes.
  • The result of an increase or decrease in the height of the land. When the height of the land increases, the sea level falls and when the height of the land decreases the sea level rises.
  • Isostatic change is a local sea level change whereas eustatic change is a global sea level change.



Define: Isostatic Uplift

Rivers have more potential energy, thus more kinetic energy, and erode more. 
The Grand Canyon formed as a result of the Colorado Plateau uplifting slowly, and the Colorado River cutting down through it.
  • Rivers have more potential energy, thus more kinetic energy, and erode more.
  • The Grand Canyon formed as a result of the Colorado Plateau uplifting slowly, and the Colorado River cutting down through it.

Define: Isostatic Depression

Rivers have less potential energy, and thus less kinetic energy and erode less.
  • Rivers have less potential energy, and thus less kinetic energy and erode less.

What is the main indicator of a river's ability to erode/transport/deposit?

Its Velocity

For any given particle size...



A river flowing fast will...?

Be able to erode

For any given particle size...



As a river slows down...?

Active erosion seases and the river is able to transport particles of that size.

For any given particle size...



As a river slows down even more...?

The river will have to start depositing those particles -- it no longer has enough energy either to erode or transport them.

As a particle size increases, what also increases?

  • The velocity required to accomplish any given process (erosion, transportation or deposition) also increases.


  • The velocity required to erode particles increases as particle size increases.

Why are river erosion and channel shape related?


  • As a river fills towards bankfull levels it becomes more and more efficient.
  • River velocities increase
  • Erosion becomes more and more powerful.

What are the three processes of river erosion?

 
Hydraulic Action
Abrasion
Solution 
 


  1. Hydraulic Action
  2. Abrasion
  3. Solution


Process of River Erosion



Define: Hydraulic Action

Physical force of river


  • The force of the water breaks rock particles away from the river channel.
  • The pressure weakens the bank and gradually wears it away.

Process of River Erosion



Define: Abrasion

Pebbles, sand etc...


  • Dragged along river bed and banks.
  • Wearing down the river bed and banks.

Process of River Erosion



Define: Solution

  • Rivers often carry mild concentrations of various chemicals (both natural and unnatural).


  • These chemicals can work to dissolve bed, banks, and particles being transported.


  • In effect, this is chemical weather, but the river is moving.

Define: Drainage Basin

The area that drains into a river.
 
 

The area that drains into a river.



Define: Tributary

A small river that joins a larger one.
 
 

A small river that joins a larger one.



What are the processes of river transport?

What are the four processes of transportation?

Traction
Saltation
Suspension
Solution 
 
 
  1. Traction
  2. Saltation
  3. Suspension
  4. Solution



Process of Transportation



Define: Traction

Large particles (i.e. boulders) are pushed along the river bed by the force of the water.

Process of Transportation



Define: Saltation

Pebble sized particles are bounced along the river bed by the force of water.

Process of Transportation



Define: Suspension

Small particles (i.e. silt or clay) are carried along the water.

Process of Transportation



Define: Solution


  • Soluble materials dissolved in water.
  • Then are carried along.

The faster the river flows...

...the more erosion that happens.

What is the river's load?

The total material carried as the be load

(traction and saltation)

+

Suspended Load

(suspension)

+

Dissolved Load

(solution)

What does a rivers behavior depend on?

The balance between its energy and its load.

What happens if a river does not have sufficient energy to transport its load?

It will begin depositing material, and become braided.

Define: Braided Channels

Numerous channels that split of and rejoin each other to give a braided appearance.
 

Numerous channels that split of and rejoin each other to give a braided appearance.


What type of profiles do rivers typically have?

Concave long profiles

What are the characteristics of upper, middle, and lower reaches or river long profiles?

Upper Reaches of River



What is the simplest way a waterfall forms?

The presence of a resistant layer of rock. 
 
 

The presence of a resistant layer of rock.



Upper Reaches of River

VS

Middle Reaches of River

VS

Lower Reaches of River

Upper Reaches of River

Characterized by: V-Shaped Valleys

VS

Middle Reaches of River

Shaped by: Meander Bends

VS

Lower Reaches of River

Characterized by: Delta

Middle Reaches of River



Define: Meander Bends


  • Tend to migrate downstream (like a snake slithering on the ground)
  • This carves our a flat plain (floodplain) with steep buffs on either side.

Middle Reaches of River



What are common features of the middle reach?


Middle Reaches of River



When meander bends cut off, what do they form?

Ox-Bow Lakes
 
 

Ox-Bow Lakes



Middle Reaches of River



Define: Floodplain Formation and Features

Middle Reaches of River



What can changes in a river's potential energy (height above base level) do?


  • Rejuvenate a river
  • Cause it to form alluvial terraces
  • Cause it to form entrenched meanders

Middle Reaches of River



Define: Alluvial Terraces

Middle Reaches of River



Define: Entrenched Meanders

Are symmetrical
Form when the river down-cuts quickly
Due to this speed there is little opportunity for lateral erosion to occur.  
 
  • Are symmetrical
  • Form when the river down-cuts quickly
  • Due to this speed there is little opportunity for lateral erosion to occur.


What are lower reaches of rivers characterized by?


Deltas

Lower Reaches of River



Define: Deltas

Where the river enters the sea
Slows down
Deposits much of the material it carries
Rivers appear as braided streams where the amount of sediment > river's ability to transport it. 
  • Where the river enters the sea
  • Slows down
  • Deposits much of the material it carries
  • Rivers appear as braided streams where the amount of sediment > river's ability to transport it.

Lower Reaches of River



What are the main types of Deltas?


  1. Arcuate Delta
  2. Bird's Foot Delta

Lower Reaches of River



Define: Arcuate Delta

Fan-shaped delta
Delta has been eroding since the construction of the Aswan High Dam, which cut off the supply of sediment.
Example: Nile Delta 
 
  • Fan-shaped delta
  • Delta has been eroding since the construction of the Aswan High Dam, which cut off the supply of sediment.
  • Example: Nile Delta


Lower Reaches of River



Define: Bird's Foot Delta

A delta with long, projecting distributary channels that branch out like the toes or claws of a bird.
Example: Mississippi Delta 
 
  • A delta with long, projecting distributary channels that branch out like the toes or claws of a bird.
  • Example: Mississippi Delta