erosion the transport of earth materials from one place to another. agents –running water (most...
TRANSCRIPT
Erosion• The transport of earth materials from one
place to another.
• AGENTS– Running water (MOST ACTIVE AGENT)– Moving air (Wind)– Glaciers
• FORCE driving all agents = GRAVITY
Erosion by water• Streams carry sediments four (4) ways:
1. Floatation – Light materials on surface.2. Suspension – materials between top and
bottom, sometimes causing streams to look muddy
3. Solution – Materials that dissolve in water (soluble materials) can’t be seen.
4. Traction – Bed load materials along bottom of stream.
Sediment size & Stream velocity
• All sediments are moving slower than the stream due to gravity and friction.
• Size of sediments that can be eroded depend on the velocity of the stream (See pg 6 ESRT).
• As velocity decreases larger sediments are deposited.
• As velocity increases lager sediments are eroded. • Become familiar with chart on page 6 ESRT and
page 261 in text.
DEPOSITION• Factors that affect RATE of
DEPOSITION:1. Particle size – The larger particles settle
fastest.2. Particle shape – The roundest ones settle
fastest.3. Particle density – The more dense sediments
settle fastest. 4. Stream velocity – As already discussed
Sorting of Sediments• Since some sediments settle faster or slower than
others they tend to get separated (sorted) by size, shape & density.
• SORTING only happens with WIND or WATER
• GLACIAL DEPOSITS ARE UNSORTED. All mixed up!!!
Two types of sorting1. Vertical sorting or Graded bedding
– Associated with still water.– Larger sediments on bottom smaller on top.
2. Horizontal Sorting• Associated with moving water that is slowing
down.• Larger sediments near the mouth smaller
sediments farter down stream.
Mission of a River• Running water (Most active agent of
weathering & erosion.• The job of a river is to lower the land!!!
1. Steep slopes = high velocity
2. High velocity = lots of erosion
3. Erosion decreases slope
4. Decreased slopes = lower velocity
5. Lower velocity = more deposition usually further down hill.
Erosion vs. Deposition along Meanders!
– Outside of Meander• Faster water (high velocity)• Deeper channel due to more erosion *SEE PICTURE
– Inside of Meanders • Slower water (lower velocity)• Shallower channel due to more deposition• Sand and Gravel bars
*SEE PICTURE
Dynamic equilibriumUPLIFT vs. EROSION
– If the forces of UPLIFT are more active than EROSION that part of the crust will appear to grow higher.
– If the amount of EROSION is greater than the amount of UPLIFT that part of the crust will be lowered.
Stages of stream development
• Rivers take hundreds or thousands of years to wear down the land. Rivers go through stages of development as they do their work.– Youthful – Mature– Old age
Youthful• Early stage of stream development.• Low volume of water (Discharge).• Very steep slopes (Gradient).• Lots of kinetic energy used to “down cut”
a narrow “V” shape (lots of erosion).• Straight path (Stream channel) for water.
Water attempts to blast through obstacles rather than go around.
Mature• Middle stage of stream development.
• Tributaries and groundwater add to stream volume.
• Slope (gradient) become less steep
• Less kinetic energy (erosion & deposition)
• Meanders Develop Stream channel begins to bend as water goes around obstacles.