Final Project Milestone 2 Phy103

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Dec 6, 2023

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1 Final Project Milestone 2: Streams and Tectonics Analysis Southern New Hampshire University PHY-103 Earth System Science

2 There are multiple topographical features seen on the map of Walterville. These features are all related to the stream processes that have occurred in the region and include drainage basins, divides, stream channels, valleys, floodplains, and oxbow lakes. Drainage basins, also known as watersheds, are formed when surface water from precipitation is moved downward into low lying areas (Lutgens et al., 2021). Drainage basins are bounded by imaginary lines called divides. In some instances, a divide can be seen as a ridge above a drainage basin. In other instances, the divide may be harder to see due to smoother topography. The water that collects at the bottom of drainage basins joins with other bodies of water to create streams and rivers. Drainage basins are seen in multiple areas of the project site topographical map, the most relevant being where the proposed project site is located. Streams either create alluvial channels or bedrock channels depending on the what type of material the stream is flowing through (Lutgens et al., 2021).. Alluvial channels are created when streams flow through loose sediment. These channels are capable of changing considerably, as it is easier for the stream to erode, move and deposit sediment Oxbow lakes are formed when an alluvial channel meanders over time and eventually encounters hard material causing erosion to slow(Lutgens et al., 2021).. An oxbow lakes is seen on the Walterville topographical map, just south of Camp Creek Road. This causes the upstream meanders to catch up with the downstream meanders. As this occurs the land that is between the meanders erodes until a portion of the river is cutoff (Lutgens et al., 2021). Bedrock channels are formed when a stream or river flows through solid rock, transporting course sediment. As channels flow through the landscape, they create valleys through erosion. Depending on the age of a river, valleys are either U-shaped or V-shaped. Younger rivers are found in V-shaped valleys like the one on the topographical map near Mount Washington(Lutgens et al., 2021). V-shaped valleys are created from the channel downcutting as

3 moves toward base level. Older rivers are found in U-shaped valleys. U-shaped valleys are formed when a river or stream can no longer downcut. Once the channel reaches base level it starts to erode the valley walls, making the valley wider, until it creates a floodplain. Floodplains are areas that are flooded when a river overflows during a flood. Floodplains are seen in proximity to the proposed project site(Lutgens et al., 2021).. The proposed project site is situated in an area at risk of flooding, mudslides, and erosion. The development is in a mountainous area with a history of heavy precipitation and overflow from streams (Southern New Hampshire University, n.d.-a). It is extremely likely that the homes within project site A and B will be subject to flooding during times of high precipitation. When looking at historical data, six out of the top ten record rainfall events have occurred in the last 20 years (Southern New Hampshire University, n.d.-b). Erosion is likely to occur due to the amount of water moving through the area. As the stream located near site A starts to meander it is likely to erode the land underneath any homes in the area. Site C is located near the edge of a drainage basin, which will cause that site to be prone to mudslides and rockslide during periods of heavy rain both in the area and at higher elevations (Southern New Hampshire University, n.d.-a). The proposed project site is near a fault line and a dormant volcano, Mount Jefferson. This indicates the potential for tectonic activity. Faults are fissures in the earth’s crust that allow blocks of rock to slide past one another to relieve built up pressure (Lutgens et al., 2021). The fault seen on the topographical map looks to be a convergent plate boundary. Convergent plate boundaries are areas where two tectonic plates move toward each other, causing one plate to be forced under the other. The area where two convergent plates meet is also called a subduction zone, due the sinking (subducting) of one plate into the earth’s mantle (Lutgens et al., 2021).. The Cascade Range where the project site is located was formed from the Juan de Fuca plate

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4 subducting under the North American plate ( Mount Jefferson | U.S. Geological Survey , n.d.). Earthquakes seem to occur on average every 70-90 years (Southern New Hampshire University, n.d.). Earthquakes in the area average a magnitude of 6.8. According to the historical data, the last earthquake along the fault occurred 85 years ago and had a magnitude of 6.9, meaning that it is probable that another earthquake will occur in the next 5-10 years, causing heavy damage in the area (Southern New Hampshire University, n.d.). Site C is in a very vulnerable area if an earthquake occurs due to its proximity to the mountains. The building in the project area are likely to be damaged by landslides and debris falling from the mountains. Sites A, B and C are likely to have damage from an earthquake due to their proximity to the various creeks and waterways in the area. The ground near the water is likely saturated, causing the ground to move in a fluid-like motion called liquefaction(Lutgens et al., 2021). The volcano in the vicinity, Mount Jefferson is a stratovolcano located in the Cascade Range. It is composed of andesite and dacite.( Mount Jefferson | U.S. Geological Survey , n.d.). If Mount Jefferson were to erupt, it could potentially cause devasting consequences. Lava is likely to flow through river valleys towards the project site, and ash and pyroclastic materials will reach areas hundreds of miles away ( Mount Jefferson | U.S. Geological Survey , n.d.). Mount Jefferson has a history of small eruptions every 600-700 years. The last small eruption occurred roughly 630 years ago (Southern New Hampshire University, n.d.). The last major eruption occurred approximately 15,000 years ago (NASA Earth Observatory, n.d.). Since Mount Jefferson erupts every 600-700 years, it is possible that a small eruption will occur in the next 50 years. If an eruption does occur the project site will be vulnerable to falling ash, pyroclastic materials, and lava flows ( Mount Jefferson | U.S. Geological Survey , n.d.).

5 References 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 Mount Jefferson | U.S. Geological Survey . (n.d.). https://www.usgs.gov/volcanoes/mount- jefferson NASA Earth Observatory. (n.d.). Mount Jefferson . https://earthobservatory.nasa.gov/images/82396/mount-jefferson#:~:text=Mount %20Jefferson%20is%20a%20stratovolcano,including%20lava%20flows%20and %20lahars. Southern New Hampshire University. (n.d.-a). 4-2 Final Project Milestone Two: Streams and Tectonic Analysis. Final Project Walterville Topographical Map . Southern New Hampshire University. (n.d.-b). 4-2 Final Project Milestone Two: Streams and Tectonics Analysis. Final Project Historical Data .

Final Project Milestone 2 Phy103

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