A.Erosion – The transportation of weathered sediments

1. Agents of Erosion or Transport Systems:

a. Running waterb. Windc. Glaciersd. Waves & Tidal Surges e. People

 2. Driving force of erosion: GRAVITYGRAVITY

 

B. EROSION BY RUNNING WATER 

1. Transport of Stream Sediments can be…

a. dissolved salts in solution

b. in a suspension

c. carried by rolling ,bouncing, sliding, or floating.

Clay particles called "Colloids" do not

settle to the bottom of a stream.

The rate of Erosion: The rate of Erosion:

Determined by the velocity of a stream.

1. Gradient: slope of the land

A steeper slope has a greater rate of erosion.

2.Volume of discharge: (Water added to the stream)

Rain or Snow

Groundwater

Tributaries

Increase Stream Velocity

A greater amount of discharge increases the rate of erosion.

TributariesIncreasing Stream Flow.

Q

A

3. Channel Shape:

Narrow channels have less surface area and reduce the friction on the water

Velocity Increases.

Streams create V- shaped valleys

4.Sediment Size and Stream Velocity

As the velocity of the stream increases the size of the sediments that can be moved increases.

  

Graph shows the velocity needed to maintain movement of a sediment, but not to start.

Stream Development:

Youthful: Steep Gradient / High Velocity / Erosion Dominate

Low Volume of Water  

Mature: Moderate Gradients & Velocity

Depositional & Erosional forces are in balance w/ flood plains 

Old: Gentle Gradients / High Velocity / Deposition Dominate

Large Volume of Water  

A Youthful Stream Narrow V-shaped Downcutting Swift water Steep gradient Erosion is dominant

Mature StreamLateral Erosion begins Meanders develop Floodplains develop Gradient lowers

Old AgeWide meanders and oxbow lakes Wide floodplain Low velocity Low gradient Dynamic equilibrium between erosion and deposition

3. The differing points of velocity within the stream.

Depends on channel shape, meanders, and surface friction. 

A. Straight Channel: Velocity greatest below the surface @ center.

B Meandering Channel:

Velocity greatest on outside of curve

Resulting in more erosion.

Velocity decreases on inside curve

Resulting in deposition.

Velocity Controlling

Erosion

&

Deposition

Deposition

Erosion

Meanders

Found in Old Streams

Low Velocity & Gradients

Deposition DominateOxbow Lakes

Flood Plains

Mississippi Floods

Pink are Metropolitan Areas

Mississippi Delta

Deposition Dominate

C. EROSION BY GLACIERSC. EROSION BY GLACIERS 

1. 1. Glaciers moved by gravity.Glaciers moved by gravity.

2. Ice actually flows (plasticity).2. Ice actually flows (plasticity).

3. Velocity greatest in the center.3. Velocity greatest in the center.

4. Form U-shaped Valleys4. Form U-shaped Valleys

GLACIAL Movements GLACIAL Movements

Flow is always from High Flow is always from High to Low elevation.to Low elevation.

U- Shaped Valleys After Glacial RetreatU- Shaped Valleys After Glacial Retreat

Slightly Filled in with DepositionSlightly Filled in with Deposition

D. Erosion by Wind

1. As wind velocity increases the size of the particles carried will increase. 

       

E. FEATURES OF ERODED SEDIMENTS  

1.Streams: Round and smooth

  

2. Wind: Angular Sediments

 

3. Glacial: Rounded with scratched surfaces called striations indicating direction of ice flow.

4. Gravity: Produces sharp angular features from the break during the fall.