PHY 103 Module 2 Assignment Phy103
docx
keyboard_arrow_up
School
Western Governors University *
*We aren’t endorsed by this school
Course
103
Subject
Geography
Date
Dec 6, 2023
Type
docx
Pages
9
Uploaded by alasmith32
1
2-1 Assignment: Stream Erosion, Deposition, and Valley Development
Southern New Hampshire University
PHY-103 Earth System Science
2
I.
Stream Erosion
The sample of water collected from the clear stream in Minnesota would contain small
particles of suspended sediment, namely clay and silt. These particles are unable to be seen with
the naked eye but are visible with a microscope. The stream is clear due to low turbidity. Low
turbidity means that the water is clear to the naked eye. Water with high turbidity will look
muddy and opaque (
Turbidity and Water | U.S. Geological Survey
, 2019).
Confluence of Waiparous Creek and Ghost River. (High and Low Turbidity)
(
Ghost River Watershed Report
, n.d.)
I let the water in the sample evaporate and found sediment that was large enough to be
seen without a microscope as the sediment was unable to evaporate like the smaller particles in
the water. As water moves downstream carrying alluvium (sediment), the sides and bottom of the
stream are eroded by the particles in a process called abrasion (Lutgens et al., 2021). The water
in the stream can and will cause erosion as well. The Green River pictured below is an example
of how abrasion works on the landscape.
3
Green River, Utah (U.S National Park Service)
(
About - Erosion: Water, Wind & Weather (U.S. National Park Service)
, n.d.)
Sand and gravel settle on the inner portion of a meandering stream due to the velocity of
the moving water. Water moves at a higher velocity on the outside of a meander, causing high
levels of erosion. The outside of a meander where the erosion is occurring is called a cut bank.
The water moves at a slower rate on the inside of a meander, causing sediment to be deposited.
These areas are called point bars. As sediment is eroded from the outside of the stream and
deposited inside, the stream moves laterally without changing shape (Van Norden, 2012).
The middle of a stream is the deepest part. This is due to the velocity of the water as it
flows downstream. The more the velocity increases, the more turbulent the flow becomes. The
turbulence is able to pick sediment up off of the streambed. The high velocity water is able to
move larger sediment and cobblestone (Lutgens et al., 2021).
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
4
(
Ausable River Association
, n.d.)
II. Stream Deposition
While in Louisiana I observed a river that was flowing into the ocean. The river was no
longer moving sediment like it had been upriver. The river had reached ultimate base level, or the
lowest point that a river can cause erosion (
Fluvial Processes
n.d.). The sediment was deposited
at mouth of the river causing the river to become obstructed. Due to the obstruction, the river
then had to create new channels, called distributaries to keep flowing (Lutgens et al., 2021). The
deposited sediment and distributaries are called deltas. The Nile River Delta and The Zambezi
River Delta are examples of deltas. During the formation of a delta, sediment is deposited in
specific ways. Fine silt and clay from the rivers’ suspended load is deposited into the ocean. This
creates what are called bottom-set beds. Fore-set beds are created on top of the bottom-set beds.
Fore-set beds are made up of coarse materials that fall immediately after they enter the ocean.
They cover the bottom-set beds. Top-set beds are created during periods of flooding. As flooding
occurs, the rivers’ course is redirected through shorter routes with higher gradients (Van Norden,
2012). As the river flows through these routes, it deposits coarse particles. When the velocity of
5
the river slows, fine sediment is deposited, which is why there may be a layer of fine sediment
over coarse alluvium.
Fine sediment has the ability to travel farther than coarse sediment. When the alluvium
reaches the ocean and ultimate base level, the coarse sediment drops down immediately, while
the fine sediment is able to be carried much further. Over time the fine sediment will become
bottom-set beds, with coarser material on top of it (Lutgens et al., 2021).
As time goes on
the delta will continue building
up to create more land. The delta will
continue to push farther out into the ocean. The land that New Orleans sits on is an example of
this. Five thousand years ago, the land that New Orleans sits on was not there. It was still part of
the ocean. As the Mississippi river has deposited sediment, its course has changed leaving new
land behind.
The Mississippi river delta is similar to another large delta, the Nile River delta in Egypt,
due to the large amounts of sediment that each river deposits into the ocean daily. They have
differences as well. The Mississippi delta is what is called a bird’s foot delta. Slow currents cause
the river to build up levees along its distributaries, creating a delta that resembles a bird’s foot .
The Nile River delta is a triangle shaped delta. Triangle shaped deltas are more traditional shaped
deltas and are created in areas where the currents are fast moving, enabling the alluvium to
spread out (Lutgens et al., 2021).
6
Mississippi River Delta
Nile River Delta
(
The Mississippi River Delta
, n.d.)
(
Delta
, n.d.)
III. Valley Development
When starting my journey into the future I start out in an area that has a small stream in
the middle of a deep, rocky canyon. I would like to see what this area looks like in the future, so
I get into my time machine and journey forward thousands of years. When I arrive the small
stream I had seen before is now a river and is flowing above a flat landscape that is separated by
hills that run parallel.
The river is no longer straight and now meanders. As time progressed the
river changed the landscape through erosion. The river originally started out with a steep
gradient, causing the water to flow rapidly (Lutgens et al., 2021). As the water flowed
downcutting occurred. Downcutting is the process of
deepening of a channel through abrasion.
Once the stream met base-level (level below which a stream can no longer erode) it could no
longer erode downwards (Lutgens et al., 2021). Because the stream could no longer direct its
energy down, it now directs it side to side, which widens its banks. The stream begins to
meander due to the velocity of the water. The out edges of stream erode, creating cut banks,
while the inner edges of the stream collect sediment creating point bars (
Fluvial Processes
n.d.).
As the stream meanders it can encounter harder material, which will cause the meanders
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
7
upstream to catch up with the meanders downstream. As the meanders catch up, the land
between the meanders erodes creating a cutoff. The portion of the stream that is no longer
receiving water is called an oxbow lake due to its shape (Lutgens et al., 2021).
The meandering river creates a floodplain as it erodes the land around it. During flooding
events, the stream overflows and overwhelms the floodplain. As the water eventually recedes,
deposits of sediment are left behind creating natural levees. As the levees form, water is unable
to flow back into the river. The areas where water is unable to flow back into the river are called
back swamps (
Fluvial Processes
n.d.). Tributaries are also created from flooding events. These
tributaries, called yazoo tributaries form when water cannot get back to the river over the natural
levees. Yazoo tributaries run parallel to rivers until it can find an area where it can reach the river
again (Lutgens et al., 2021).
My journey to the future has shown me the evolution of a stream to a river and the way
water can change the landscape. Eventually the small stream in the canyon will become a
meandering river along a wide floodplain with natural levees, yazoo tributaries and back
swamps.
8
References
About - Erosion: Water, wind & Weather (U.S. National Park Service)
. (n.d.).
https://www.nps.gov/subjects/erosion/about.htm
Delta
. (n.d.).
https://education.nationalgeographic.org/resource/delta/
Fluvial Processes. (n.d.).
https://learn.snhu.edu/d2l/le/content/1388689/viewContent/26546941/View
Ghost River Watershed Report
. (n.d.). Ghost Watershed Alliance Society.
https://experience.arcgis.com/experience/375d5964d3884420b0345081c8ef9615/page/Su
rface-Water-Quality/
Lutgens, F. K., Tarbuck, E. J., & Tasa, D. G. (2021).
Foundations of Earth Science
(9th ed.).
Pearson Education (US).
https://bookshelf.vitalsource.com/books/9780135851609
NASA Earth Observatory. (n.d.).
Zambezi River Delta
.
https://earthobservatory.nasa.gov/images/82361/zambezi-river-delta
The Mississippi River Delta
. (n.d.). National Environmental Satellite, Data, and Information
Service.
https://www.nesdis.noaa.gov/news/the-mississippi-river-delta
Turbidity and water | U.S. Geological Survey
. (2019, October 22).
https://www.usgs.gov/special-
topics/water-science-school/science/turbidity-and-water#:~:text=Turbidity%20is%20the
%20measure%20of,light%2C%20the%20higher%20the%20turbidity.
Van Norden, W. (2012, July 26).
River erosion, transport and deposition.mov
. YouTube.
https://www.youtube.com/watch?v=E6sWiPAu708
9
Why do streams meander? | Ausable River Association
. (n.d.).
https://www.ausableriver.org/blog/why-do-streams-meander
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help