2-1 Stream Erosion and Deposition PHY 103 PDF

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Download 2-1 Stream Erosion and Deposition PHY 103 PDF

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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? a. A sample of water when observed under a microscope would contain tiny sediment grains that were eroded. Due to natural processes like downcutting and lateral erosion the nearby landscape will be hugely altered causing the material, like rocks and sand, to be moved to a new place further down. B. Next you let a sample of the water evaporate. What might you find in the collection dish once the water is gone? Why? a. If evaporated, tons of sediments created through the process of erosion would be found in the collection dish. Carbonate sediments would be left behind due to the fact they have grown too big to dissolve in the water. C. You also note that sand and gravel form the inside riverbed of the stream meanders. Clarify where the sand came from and why it is found where it is. a. The sand found inside the riverbed of the stream meanders came from an upstream that was eroded over time due to weather and water naturally running through the stream. Bigger and heavier grains are let go because the stream can’t continue to carry the load which, in turn, causes the meander to accumulate high energy, increasing water 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. a. In straight channels, the highest velocity occurs in the middle. The deepest part of the stream occurs at its highest velocity hence why the deepest part is in the middle where the cobblestones are. They sit there because they are too heavy for the stream to carry so they remain there. 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. a. Oceans are main drainage basins for the rivers. Erosion caused throughout the river would end at ocean level because a lot of the energy is lost when it reaches the sea. B. Detail how and why the river channel breaks into many near the coast. a. The river channel breaks into many near the coast due to the appearance of deltas. Deltas are large silty areas that occur at the mouth of the river as it enters another body of water. Deltas form as a result of the river becoming shallower. C. Explain why you are standing on a layer of very fine soil, yet just beneath you are layers of coarse alluvium.

a. This most likely occurs due to you standing on an area of land that has been affected by transgressions and regressions. A marine transgression can be explained as a geological event that occurs when the sea level rises causing the shoreline to move toward higher ground, resulting in flooding. 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 over time. a. A river with high velocity transports high amounts of dissolved solids farther out, eventually extending beyond the mouth, as its coast pushes further out. Very fine sediments are found far offshore because they are low energy environments. 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? a. The Mississippi drainage basin delta in Louisiana is at the river’s mouth where the stream’s velocity and gradient has largely slowed and bottomed out, reaching its base level. 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? a. The landforms are largely similar, but the Nile River and its impact on the surround land exists on a much grander scale since it is longer and much wider. The Nile is over 4,000 miles long whereas the Mississippi river is only 2,320 miles. 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. a. During this rather young stage of a stream, it is in the process of establishing a new drainage system. These younger, high gradient streams could also be Yazoo streams. A stream that runs parallel to a low gradient river until the high gradient stream eventually meets up and connects to the wider, more developed river. Downcutting and headward erosion are the major processes of river erosion. These processes will play a huge part in developing the small, young stream into a more mature version or could potentially become an oxbow lake. An oxbow lake is U-shaped lake that forms when a wide meander of a river is cut off,

creating a free-standing body of water. There are lots of possibilities that the pubescent stream can become given enough time and the proper conditions....