2-1 assiment stream erosion
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Southern New Hampshire University *
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103
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Geography
Date
Dec 6, 2023
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docx
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[Document title]| Sam Shock
I. Stream Erosion: Imagine you are on location in Minnesota. You note that the water in the stream you
are analyzing is clear. You take a sample of the water and look at it with a microscope.
A. What will you find, including details of origin and relation to landscape alteration?
The sample under the microscope would show tiny sediment grains that were eroded.
Natural processes like downcutting and lateral erosion the nearby landscape will be
altered causing the material, like rocks and sand, to be moved to a new place.
B. Next you let a sample of the water evaporate. What might you find in the collection dish once the
water is gone? Why?
If the water evaporated, it would leave behind carbonate sediments because they are
two big to dissolve in water.
C. You also note that sand and gravel forms the inside riverbed of the stream meanders. Clarify where
the sand came from and why it is found where it is.
The sand and gravel that forms the inside riverbed of the stream menders came from
the upstream that was eroded naturally running down the stream. Bigger and heavier
grains stop where they are found because the river load cannot carrier them, which
causes the meander to accumulate high energy, increasing flow.
D. Next you find that the deepest portion of the stream is near the middle. Cobblestones occupy the bed
there. Explain how that is possible and why the stream is deepest in the center.
The highest velocity occurs in the middle of straight cannels. The cobblestones occupy
the middle of the bed because they are too heavy for the stream to carry so they stay
there. It is possible because the deepest part of the stream occurs at the highest
velocity.
II. Stream Deposition: You are at a second location, near the coast in Louisiana.
A. Explain what the ocean represents relative to the river and why and how erosion from the river will
not extend past the ocean level.
The main basins for rivers are oceans. The erosion from the river will not extend past the
ocean level because the lost of energy is lost when it reaches the sea. Also, the steam
reaches the base leave when it enters the ocean the velocity quickly reaches zero.
B. Detail how and why the river channel breaks into many near the coast.
The river channel breaks down too many near the coast because of the deltas. Deltas are
large silty areas that occur at the mouth of the rives as it enters another body of water
deltas form because the rivers are becoming shallower do to sediment deposited
slowing the water.
C. Explain why you are standing on a layer of very fine soil, yet just beneath you are layers of coarse
alluvium.
[Document title]| Sam Shock
The layers of coarse alluvium may be beneath us because the soft rock us eroding under
the hard cap do to headward erosion. It could also be alluvium because of a geological
event like a flood causing the shoreline to move above sea level.
D. Discuss why beds of very fine sediment are found far offshore and where these will be if the current
landform extends farther out to sea overtime.
Rivers with high velocity transports high amounts of dissolved solids farther out, causing
it to extend beyond its mouth. The fine sediments are found offshore due to the high
transports and then having low velocity pushing it back.
E. Integrate all of the concepts above to fully explain the surrounding landform, including the surface and
extending downward into the sedimentary layers. How has the landform changed over time and why?
Mississippi drainage basin delta in Louisiana is at the mouth where the steam velocity
and gradient are slowed down and stopped. Landforms such as dunes or deltas appear.
F. Finally, compare the present landform of this river to a similar but vastly different landform associated
with the Nile River in Egypt. How are the landforms similar? Different? Why?
The similar is that they are both primarily composed of a fine and nutrient rich silt. The
dispositions process is almost the same. Erosion creates particles and deposits them
accordingly based on the energy and size ratio.
III. Valley Development: You have control of a time machine. Your journey into the far future begins in a
deep, rocky canyon, inhabited by a small stream in the center. Your journey ends in the same location,
but the landscape has changed to one that is flat in every direction for as far as you can see. The stream
is present, lies generally above the surrounding landscape, and is separated by hills that parallel the
channel on either side. You note that the stream is much larger than the one you left in the past.
A.
Fully detail and discuss the evolution of the landscape from a high gradient one to that of a low
gradient, well-developed, and wide floodplain over time. Be sure to list and detail all relative
landforms and stream characteristics (meanders, oxbow lakes, Yazoo streams, natural levees,
etc.) that result as the landscape alters with each phase over time.
The younger streams are providing and establishing a new drainage system. The younger
stream could also be Yazoo streams. A stream that runs parallel to a low gradient river
until the high gradient stream meets up to a wider more developed river. Down cutting
and headward erosion are the process of river erosion. Then it will turn in to an oxbow
lake. An oxbow lake is a U-shape lake that forms when a wide meander of a river is cut
off. Natural levees are slopes of sand or mud built up along the side of rivers or streams.
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