4-2 Milestone Two-Streams and Tectonics Analysis

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Dec 6, 2023

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Leticia Pollard-Torres PHY 103-Prof. Lynda Folts 4-2 Final Project Milestone Two: Streams and Tectonics Analysis There were several areas identified as sites of interest in the survey. The landscape contains features that are directly related to stream processes. In this survey, we analyze the topography, historical data on volcanoes and earthquakes, and how the tectonic plates change the landscape of the area under study. This study aims to describe all the landscape features, formations, and potential hazards that may affect human life in the area in question. Landscape Features: Our investigation sites are located near a subduction fault approximately 60 miles from Mount Jefferson. In the Cascade Range, Mount Jefferson is a dormant stratovolcano that last erupted approximately 7,600 years ago. Mount Jefferson is the second- highest peak in Oregon at 3,199 meters (10,495 feet). In the past, there have been other eruptions that have not been recorded due to erosion caused by glaciers. Because of this, U-shaped valleys are clear, and rivers carve their way down the valley. We can also see the meanders of the McKenzie River eroding the outer banks and depositing sediment on the inner banks or point bars. A flood plain area is present along the McKenzie River at Site A, and moving down the map, we locate project site B. This site is located near the fault associated with the Cascadia Subduction Zone off the coast of North America . Located at the boundary between the Juan de Fuca plate and the North American plate, the Subduction Zone is a divergent plate boundary (Banse, 2019). Located on the Juan de Fuca plate, the volcanic arc makes this area known as the ring of fire. Our project area site C is situated at a high elevation, looking down to the river below.

Geologically, this area is composed of igneous, metamorphic, and sedimentary rocks. The spectacular landscape of Oregon has been shaped over millions of years by fire and flood, earthquakes, and eruptions, as well as massive movement of oceans and continents (DOGAMI - Oregon Department of Geology and Mineral Industries, n.d.). Sites Analysis: Site A : The site is stable, but this area still presents several geological hazards. In addition, the meanders are prone to flooding during heavy rainfall, which could lead to sediment erosion and deposits in the point bars. This can cause changes to the river's course and potentially lead to the formation of oxbow lakes. Furthermore, the sediment deposits can cause the river's depth and flow to change, affecting the water quality and potentially leading to the destruction of aquatic habitats. During this survey, we discovered that there is an abundance of rainfall at the beginning of the year. In January, the maximum rainfall was 19.84 inches, and the average river elevation was 34.11 feet. Those living in this region would have suffered great losses, crops would have been destroyed, and domestic animal farms would have been submerged. Site B : Due to the convergence of the Juan del Fuca Plate and the North American Plate, mountains and hills have developed. This process is known as subduction and happens when one tectonic plate slides underneath another. Mountains and hills are formed because of the movement of the oceanic plate beneath the continental plate. Site B is susceptible to land and mudslides, as well as soil erosion, due to its steep slopes and heavy rainfall. Site C : This area is situated in a mountainous area overlooking the river over Site A, the floodplain zone. The area's geology is composed of sedimentary and volcanic rock. The age of these rocks is generally between 60 million and 2 million years old (DOGAMI - Oregon

Department of Geology and Mineral Industries, n.d.). Mountains in the area have been uplifted because of soil movement caused by the fault that passes through the region. Fluvial features from erosion: Under close inspection all sites have floodplains and rivers that flow through them. These streams and rivers have shaped the landscape over time. These waterways provide an important habitat for local wildlife and are essential to keeping the environment healthy. They are also a source of recreation and an important part of the local culture. However, they can also pose a significant risk to those living in flood-prone areas. Site A: A river that flows on a floodplain may once again produce a floodplain at a lower level after adjusting to a relative drop in base level. A relative drop in base level is characterized by stream terraces. The formation of terraces occurs when a stream flowing on thick alluvial deposits adjusts to a relative drop in base level ( Lutgens et al., 2021). The topographic map shows this in section A. Site B : Under site B, there is a river that meanders creating a steep cut bank. This cut bank is eroding over time, making the river wider and shallower. This erosion can cause significant damage to the surrounding environment, as it can lead to sediment buildup and destruction of aquatic habitats. The McKenzie River has unique geology. There is no other place like Oregon's lava capped Cascades, which store and release McKenzie's crystal-clear water ( Making the Case – McKenzie River Discovery Center , n.d.). Site C : Over time, the river erodes away the river valley sides and deposits sediment downstream. This creates an area of land that is typically wide and flat, which is why Site C is

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the most suitable location for future development. However, precautionary actions need to be taken as steep slopes or unstable soil can lead to landslides as we have learned in this course. Tectonic elements and potential hazards in the area: Among the geological hazards present in the region, the subduction fault stands out as the most significant. As a result of subduction zones, oceanic crusts older than 200 million years cannot be found (Libretexts, 2020b). Site B is the site nearest to this fault, followed by site C, which is in a mountainous region caused by upliftment of the terrain. Several factors contribute to this situation, including the possibility of earthquakes and volcanic eruptions in the area. Based on data collected from Mt. Jefferson historic data, the last volcanic activity was over 631 years ago. Mt. Jefferson is an active stratovolcano located in the Cascade Range of the Pacific Northwest in the United States. It is the second highest mountain in Oregon and is part of the Cascade Volcanic Arc. The tectonic activity in the area can impact the population and could potentially put their lives at risk. Structures in the area may sustain structural damage due to the fault, the terrain may go through the process of liquefaction in flood zones, and landslides may damage nearby residential areas. Liquefaction is when an earthquake motion turns loosely packed, water-saturated soil into liquid (CEA - Soil Liquefaction , n.d.). In these areas of development, several measures should be implemented to mitigate these risks. For example, earthquake-resistant buildings and infrastructure, evacuation plans for volcanic eruptions and floods, and monitoring for signs of activity at the volcano and fault line. Additionally, emergency response teams should be trained and equipped to handle such natural disasters. Early warning systems should also be put in place to alert the public in the event of a disaster.

Conclusion: In conclusion, the area where we conducted our analysis has been through many changes over millennia. As the human population has settled in these areas and despite the risk, population growth continues, and more land is utilized for farms, crops, and watershed to sustain the population living here. Since the plates are constantly moving under the earth's crust, disaster can strike at any moment. Therefore, it is important to understand the history of the landscape and the geological risks present to plan for potential disasters. Understanding the area's landscape and the risks it poses can help to mitigate potential disasters and save lives.

References: NASA Earth Observatory. (n.d.). Mount Jefferson . https://earthobservatory.nasa.gov/images/82396/mount-jefferson Banse, T. (2019). The Big One — And Another One. Research Shows Cascadia Quakes Sometimes Trigger San Andreas. Northwest Public Broadcasting . https://www.nwpb.org/2019/12/03/the-big-one- and-another-one-research-shows-cascadia-quakes-sometimes-trigger-san-andreas/ Risley, J. (2015, November 13). Surprises emerge as scientists map the tectonic plate that could cause ‘The Big One’ GeekWire . https://www.geekwire.com/2015/surprises-emerge-as-scientists-map-the- tectonic-plate-that-could-cause-the-big-one/ Libretexts. (2020). 2.5: Types of plate boundaries. Geosciences LibreTexts . https://geo.libretexts.org/Bookshelves/Oceanography/Book%3A_Oceanography_(Hill)/02%3A_Earth %3A_Formation_and_Structure/2.5%3A_Types_of_Plate_Boundaries DOGAMI - Oregon Department of Geology and Mineral Industries. (n.d.). Oregon: A Geologic History - Introduction . https://www.oregongeology.org/pubs/ims/ims-028/index.htm Lutgens, F. K., Tarbuck, E. J., & Tasa, D. G. (2021). Foundations of Earth Science (9th ed.). Pearson Education (US). https://mbsdirect.vitalsource.com/books/9780135851616 Making the case – McKenzie River Discovery Center . (n.d.). https://www.mckenziediscoverycenter.org/making-the-case/ Libretexts. (2020b). 2.5: Types of plate boundaries. Geosciences LibreTexts . https://geo.libretexts.org/Bookshelves/Oceanography/Book%3A_Oceanography_(Hill)/02%3A_Earth %3A_Formation_and_Structure/2.5%3A_Types_of_Plate_Boundaries CEA - Soil liquefaction . (n.d.). https://www.earthquakeauthority.com/Prepare-Your-House-Earthquake- Risk/Geologic-Hazards/Liquefaction Southern New Hampshire University. (n.d). PHY 103 Final Project Site Topographic Map. Retrieved from http://snhu- media.snhu.edu/files/course_repository/undergraduate/phy/phy103/phy103_final_project_site_topographi c_map.jpg . Southern New Hampshire University. (n.d).). PHY 103 Final Project Waterville Topographic Map Retrieved from https://snhu- media.snhu.edu/files/course_repository/undergraduate/phy/phy103/phy103_final_project_walterville_top ographic_map.jpg

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