Unit 4: Deposition

Do Now: What happens to all this transported material?

1.  Cause: Erosion agent’s motion stops. Water decreases in velocity.

2.  Location:

  1. ______of a meander
  2. where a stream enters a still body of water forming a delta (Niger river delta)
  3. where a stream exits a narrow steep valley forming an alluvial fan (Bonneville salt flats)

3. Factors Affecting Deposition : (keeping all other factors constant)

a. Particle Size vs. Settling Time:

______

b.  Shape:

______

c.  Density:

______

4. Particle Property Results:

When water velocity slows, particles begin to settle out. What could cause water to decrease in velocity?

#1. A stream enters a still body of water

#2. A stream’s discharge decreases (dry season)

#3. ______

Factor #1 causes horizontal sorting. This occurs when the largest and most dense particles settle nearest the mouth of the stream and the sediments decrease in size as you continue out to sea.

horizontal sorting

Factor #2 causes vertical sorting. When the stream velocity is decreasing, the largest particles settle first and the grain sizes decrease as one observes up through the bed. This will often occur repeatedly in a particular location due to seasonal or other variations in stream velocity.

Wow, that dude is excited about graded bedding!

5. Erosional / Depositional Systems:

a. Either erosion or deposition may be dominant at a particular location. Label the diagram where you think the following terms/conditions apply.

A) Erosion dominant

B) Deposition dominant

C) Interface between erosion and deposition

A state of dynamic equilibrium between erosion and deposition exists within the system where erosion and deposition rates are equal (C).

6. Stream Life Cycle:

A Youthful Stream (Upper Course)

Narrow V-shaped

Downcutting

Swift water

Steep gradient

Erosion is dominant

Mature Stream (Middle Course)

Lateral Erosion begins

Meanders develop

Floodplains develop

Gradient decreases

Old Age (Lower Course)

Wide meanders and oxbow lakes

Wide floodplain

Little downcutting

Low velocity

Low gradient

Dynamic equilibrium between

erosion and deposition

Where does the energy come from that gets the water back to the top of the mountain? ______