Stream Erosion, Deposition, and Valley Development: A Comprehensive Analysis, Cheat Sheet of Earth Sciences

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2-1 Assignment: Stream Erosion, Deposition, and Valley Development Laura Spradley Southern New Hampshire University PHY103: Earth System Science Lynda Folts November 6,

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. When a water sample is examined under a microscope, microscopic grains of degraded sediment are visible. The material, such as boulders and sand, will be relocated to a new site further down as a result of natural processes such lateral erosion and downcutting, which will significantly modify the adjacent terrain. 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. Tons of sediments produced by erosion would be found in the collection dish if they evaporated. Since carbonate sediments had gotten too massive to dissolve in the water, they would be left behind. 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 that was discovered inside the meandering riverbed of the stream originated upstream and was worn over time by weather and water that naturally flowed through the stream. Larger and heavier grains are released into the stream because they can no longer support their weight, which in turn causes the meander to build up high energy and increase 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. As the coast pushes farther out, a river with high velocity delivers high concentrations of dissolved materials farther out, finally extending beyond the mouth. Because the settings offshore are low energy ones, very fine sediments can be found there. E. Integrate all 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. At the river's mouth, where the stream's velocity and gradient have largely slowed and bottomed out, reaching its base level, is the Mississippi drainage basin delta in Louisiana. 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 basically comparable, but because the Nile River is longer and wider, it has a far larger impact on the surrounding area. The Mississippi River is only 2,320 miles long, while the Nile is approximately 4,000 miles long. 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. a. A stream is developing a new drainage system at this relatively early stage. These more recent streams with steep gradients might also be Yazoo streams. a stream that follows a low gradient river until it ultimately intersects with the high gradient stream and joins the larger, more developed river. The two main factors that cause river erosion are downcutting and headward erosion. These activities will have a significant impact on how the small, immature stream matures and possibly turns into an oxbow lake. An oxbow lake is a U-shaped body of water that develops when a large river meander is severed and left to stand alone. Given enough time and the right circumstances, the adolescent stream has a wide range of potential outcomes.