PHY 103 Module 2 Assignment Phy103.docx

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).

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

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