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Stream Erosion
 Running
Water
 Energy
 The water
cycle
 Most effective agent in
wearing down the surface of
the earth
 From the sun… Powers the
running water.
 One of earths many cycles it
is energized by the sun and
circulates all of the earths life
giving water.
 Bedrock
Breakup
 Occurs in 2 ways.
 Mechanical means– Using sand
gravels and small rocks the water
grinds at the bedrock. Boulders
are also used as cutting tools.
 This grinding action is called
Abrasion.
 Abrasion—also causes the cutting
tools to be worn down. Especially
at their edges.
Cutting Tools can be very small and as big as cars.
 Chemical
Means--
 Consists of dissolving soluble
minerals limestone and marble
and sandstones that are held
together with calcite cements.
 Rivers flowing over such rocks
form pits and holes in the bed
rock.
 Transportation
 Rivers carry rock materials in
3 ways.
 1. Solution– dissolved
materials from bedrock. Ex.
Calcium , magnesium
 2. Suspension– includes clay,
silt, and fine sand. Although
these materials are heavier
than water they are stirred up
and kept from settling on the
bottom by the water moving.
 3. Bed load– Sediment moved
along the stream bottom. Ex
large cobbles and boulders.
 Load Of the
stream
 Estimate what percent of the
load of the stream is solution
suspension and bed load.
 Solution 25%
 Suspension 50%
 Bed Load 25%
 Note– in General the suspended
load increases with human
activity.
 Carrying
Power
 Is indicated by both the total
amount of sediment in the stream
and by the particle size being
moved.
 The carrying power depends upon
the speed of the stream and its
discharge.
 Discharge
 Is the volume of water flowing past
a given point in the stream at a
given time.
 Expressed in CFS
 Cubic feet per second.
Waterfalls and River Deposits
 Potholes
 As sand –pebbles and small
boulders swirl around in the
turbulence of a stream they grind
deep oval holes into the stream
bed.
 Very large potholes are called
plunge pools. And form through
abrasion or dissolving of minerals.
 Found at the base of waterfalls.
 Waterfalls
 NOTE
 Occur for many reasons
1. River may flow over hard rock
onto a softer one.
2. Glaciers erode one valley
deeper then others coming
into it.
3. Intrusions of igneous rock


Rapids and waterfalls are only
temporary features of streams.
http://www.youtube.com/watch
?v=_HFmxRicX4o
Harder Rock.
More Resistant
Softer Rock
 Undermining
 Erosion of the base of the water
fall leaves an overhang that is
susceptible to falling off.
 From time to time pieces break
off the top of the fall and thus it
recedes farther upstream.
 Meanders
 A series of broad curves in the stream
bed.
 Form when water moves slowly across
a wide flood zone.
 Also forms oxbow lakes and cutt offs
from the river channel.
Creation of a Meander
and cut offs and ox
bow lakes.
Flow direction
Formation of Meanders
Point
bar
deposits
Formation of an Oxbow
Cut bank erosion
Point
bar
deposits
}
Meander
loop
River Deposition
 Speed of the
river
 Dictates how much and what
size sediments fall out of the
moving water.
 Greatest loss of speed is when
a river flows into a standing
body of water. Or the water
source is cut off.
 Identify an example in nature
when a river would loose
water.
Answer: Loss of
both discharge
and speed
This is a photo of a car buried in flood
sediments. Question : Why does a river leave
so much sediment on its valley floor after a
flood?
Deltas - Distribution
Systems
Alluvial Fans
Transition in speed.
Assignment: Complete the
following.
1.
Explain How running water gets its energy from the sun.
2.
Describe ways– in which running water breaks up bedrock.
And how running water transports rock material.
3.
Discuss the relationship between stream speed, discharge and
carrying power.
4.
Draw a diagram and explain how a waterfall occurs and how it
migrates.
5.
Explain the origin of the following: use a diagram to help you in
your explanation.
6.

Meanders, flood plains, cut offs, oxbow lakes, Deltas and
alluvial fans.
The River Valley
The “V”
shape
“V” shaped valleys are typical
of young streams and river
systems.
They occur this way due to the
fact that young streams tend to
flow at higher speeds which
easily scour the stream bed.
Steep valleys are called
canyons, gorges, or chasms.
How long does it take to cut a
deep canyon?
Depends…
Kind of bed rock.
The amount of water.
The amount of sediments.
Base Level
A stream con not cut its bed any
lower than the level of the stream
river or body of water into which it
flows.
Ex. Streams that flow into the
ocean the base level is sea level.
What would the Boise river’s
“base level be”?
As a stream approaches its
base level, the slope of the
streambed and the speed of the
stream decreases.
As a result the streambed
weathers slower and slower.
At the same time the valley
walls are being eroded and
weathered by tributary streams.
The Final result is a wider river
valley.
If vegetation is removed by
natural or man caused methods
this sets up a dangerous
situation in nature.
Drainage Basin
Or water shed. Includes all the
land that drains into the river,
either directly or through its
tributaries.
What is the largest single
drainage basin in the US???
Mississippi River drainage Basin.
What is the largest basin in the
world?
Erosion Poster Guidelines
Bold Title
Catchy subtitle
Include five topics
about your type of
erosion
Three diagrams
illustrating agent
processes
Colored
Sketch or create
digitally
Erosion Types:
•Mechanical vs.
Chemical Weathering
•Stream Erosion
•Wind Erosion
•Glacier Erosion
Erosion Poster Project
Black TextbookStreams- pg.168
Glaciers- pg. 190
Wind- pg. 210
Red TextbookStreams- pg. 272
Glaciers- pg. 291
Wind- pg. 301
Stream Carrying Capacity
Review
Black Text Book
Pg. 176- 5,6
Pg. 182- 13, 15
Pg. 185- 16,17,19