Milestone 1 Phy103

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Dec 6, 2023

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1 2-2 Final Project Milestone: Geologic Analysis. PHY-103 Earth System Science Southern New Hampshire University

2 The rock types present in the project areas stratigraphy and cross section in order from the surface down are limestone (A), sandstone (B), granite (I), limestone (C), coal (D), siltstone (E), coal (F), sandstone (G), and schist (H) (Bergmann, 2011). The first layer, limestone is a biochemical sedimentary rock and is mostly comprised of calcite (C a CO 3 ) King (n.d.) . Sandstone is a clastic sedimentary rock and is made up of mainly quartz and clay (GeoKansas, n.d.). Granite is an intrusive igneous rock, meaning that it is formed deep within the earth from cooled magma rock (Lutgens et al., n.d). Like limestone, coal is also a sedimentary rock. Unlike limestone, it is an organic sedimentary rock made up of once living organisms that have been compressed rock (Lutgens et al., n.d). Schist is the last of the rock types that are present within the project area. Schist is a foliated metamorphic rock that has shale as a parent rock (King, n.d- b.) . Sediment is usually deposited in layers with the bottom layers being the oldest and the top layers being the youngest. There are exceptions to this rule, in the form of dikes and sills. Dikes are incongruous areas that form in the rock layers from magma that is forced upwards through the sediment layers (Lutgens et al., n.d). Sills are horizontal areas, the result of magma that finds weak spots in rock structures (Lutgens et al., n.d). The oldest sediment layer is schist. The schist layer is at the bottom of the stratigraphy, located underneath the other layers. Even though granite is underneath the schist, it is a younger rock, due to its presence throughout the layers and into the sandstone layer B (Bergmann, 2011).. The next oldest layer is sandstone, then coal, siltstone, coal again, limestone, and sandstone, as they are located above the bottom layer. Layer A is limestone and the youngest layer, due to its location at the top of the other layers (Bergmann, 2011).

3 Limestone is usually formed in warm shallow saltwater but can be formed in lakes and hot springs as well (Basics-Depositional Environments, n.d.). Sandstone generally forms in basins both near and far from water after minerals are washed down and compacted over time (GeoKansas, n.d.). Limestone and sandstone are layered together in the stratigraphy, meaning that they were formed in or around water. Siltstone is found near rivers and streams that weave through floodplains. Schists are formed when shales and sandstones are subjected to heat and compression (King, n.d-b.) Coal is found in areas that are damp and abundant in plant debris(Lutgens et al., n.d). The included soil profiles give insight into the potential for erosion. Soil profile A has four horizons. The first horizon, O, is made up of organic matter. Horizon A is next and is made up of topsoil, B is subsoil and C is the substratum, which is weathered or poorly weathered rock ( Soil Horizons - Soil Ecology Wiki , n.d.) . Horizon O is not always present in soil profiles. The occurrence of this horizon means that at some point organic matter covered the topsoil. Soil profiles B and C do not have an O horizon. This could be due to glacial movement or changes in the boundaries of streams and rivers ( how parent material affects soil profile development n.d) . The project area is in the Cascade Range. Soil and sediment have been moved from higher in the Cascades, down to the project area, causing different profiles ( how parent material affects soil profile development n.d) . The topological map of the project area shows many streams and rivers, creating the possibility of flooding. The stratigraphy shows two layers of limestone, which indicates that the area has flooded before (Basics-Depositional Environments, n.d.). In years with high precipitation the likelihood of flooding increases exponentially. The project area is located within an area with a volcano as well as a known thrust fault. The thrust fault is visible on the site stratigraphy and cross section as well as on the

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4 topographical map. Thrust faults are found in subduction zones, meaning areas where the lithosphere (crust and upper mantle) is sinking back into the mantle. Earthquakes at thrust faults occur due to severe compressional stress (Lutgens et al., n.d). The presence of a fault in the project area opens the possibly of earthquakes. These earthquakes may be small, but there is a chance for a larger earthquake to happen. There is a volcano in the vicinity as well. While it is unlikely that the volcano itself will erupt, it is possible that an earthquake could cause magma to be forced to the surface, causing fires or destruction of the subdivision. The project is also in a floodplain, surrounded by rivers and streams. This can bring the possibility of flooding. 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

5 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 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

6 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 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.).

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7 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 area (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.).

8 References Basics--Depositional environments . (n.d.). https://commons.wvc.edu/rdawes/g101ocl/basics/depoenvirons.html#:~:text=A %20depositional%20environment%20is%20a,are%20sometimes%20called %20sedimentary%20environments . Bergmann, J. (2011, February 6). How to read a geologic map (3/3) [Video]. YouTube. https://www.youtube.com/watch?v=5EZbHCxv0NY King, H. M. (n.d.-a). Limestone: Rock uses, formation, composition, pictures . https://geology.com/rocks/limestone.shtml King, H. M. (n.d.-b). Schist: Metamorphic Rock - Pictures, definition & more . https://geology.com/rocks/schist.shtml 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. Sandstone | GeoKansas . (n.d.). https://geokansas.ku.edu/sandstone 3.6 - How Parent Material Affects Soil Profile Development | Soil Genesis and Development, Lesson 3 - Soil Forming Factors - passel . (n.d.). https://passel2.unl.edu/view/lesson/2b7d02fa1538/6

9 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 .

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