Topic: Erosion & Running Water
* Earth’s main agent of natural erosion
What is erosion?
• Erosion is -
Agents of Erosion
• Agents of erosion include --• Running water is the big Kahuna of all
erosional agents.
How does water carry the sediments?
• Water carries sediments in the following ways:–Solution – -–Suspension – -–Rolling or bouncing along the streambed.–Floating – -
River Floor
Flow of the River
Cobbles & PebblesMove by sliding, rolling along the river floorSlower than the water flow
SandBounces along river floorSlower than the water flow
Colloids (Silt & Clay) & Dissolved IonsCarried in suspensionSame speed as water
Streams act as conveyor belts
Lake
Ocean
Stream Side ViewGreatest Potential Energy = Stored Energy
Greatest Kinetic Energy = Energy of Motion
Low Kinetic & Potential Energy
Most Erosion
Most Deposition
Dynamic EquilibriumRate of Erosion = -
Changing Stream Velocity:
• A. --• B. --
Stream velocity determines size of sediment carried.
ESRT pg 6 Take out your ESRT!
Streambed--
--
Stream bank
Stream bank
Region of maximum stream velocity changes when streams bend or turn.
Stream
Region of maximum velocity shifts to --
Region of minimum velocity shifts to --
Since the region of maximum stream velocity is at the outside of the curves, streambeds are more eroded at the outside of curves.
Stream
A
A’
B
B’
C’C
AA’Streambed
B’ B
StreambedC C’Stream
bed
What does erosion by rivers create?
• Abraded sediments– --
FQ
The stream’s velocity is 100 cm/sec, what size sediment(s) can the stream transport?
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Topic: Life Cycle of a Stream
Youthful Stream
Steep Slope Rapid
Flow
Lake
(Source of Water)
Rapids
Waterfall
This forms V-shaped valleys.
** ---**
Middle AgeVelocity decreases
due to decrease in slope
Downcutting slows due to velocity decrease
Valley walls become wider
Begins to meander
Old Age Stream Slow speed
Almost flat slope
Very little erosion
Wide meanders
Oxbow lake
Wide flood plain
Very broad, flat valley (flood plain) filled with fine sediments - alluvium
Meander – --
Oxbow lake – --
Rejuvenation – a stream may be brought back to a youthful stage of development at any time by uplifting the land.
(ex. Grand Canyon)
Name the part of the stream’s life cycle in the
picture
FQ:What shape do stream valleys make?
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