Lab 7 GEO

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65 Exercise 7 Coastal Processes and Hazards James S. Reichard Georgia Southern University Student Name: Kevin Hoffman Section _______ In this lab, you will: examine different types of shorelines and associated coastal hazards. You will also explore how coastal processes are disrupted by various shoreline engineering techniques. Background Reading and Needed Supplies Prior to doing this exercise, you should read Chapter 9, Streams and Flooding in the textbook. With respect to supplies, you will need a calculator, ruler, and colored markers. Part I – Coastlines and Human Development Recall from the textbook that tectonically active shorelines are usually rugged and irregular, with beaches often restricted to coves. In contrast, passive shorelines have little to no tectonic activity, which commonly results in relatively straight coastlines with flat-lying terrain and extensive beaches. The cross-section in Figure 7.1 illustrates the general tectonic setting of active and passive shorelines. For a variety of reasons, people have historically built settlements in coastal areas. Today, the rate of population growth is significantly higher in coastal zones than in the interior of continents. Figure 7.1 1) Describe the general types of coastal hazards one would expect to find along tectonically active shorelines and passive shorelines. active shorelines : Refer to the parts of the coast that are directly influenced by the waves at some point in the tide. passive shorelines: Ex 7 – Coastal Hazards

The transition between oceanic and continental crust is not an active plate boundary. 2) The satellite photo in Figure 7.2 shows the area around Hanauma Bay on the Hawaiian island of Oahu. Note the extinct cinder cones, one of which has been breached by wave action, forming a small bay. a) Using a red-colored marker, outline the boundary between the developed and non- developed areas on this photo. b) Note how abrupt the boundary is between developed and non-developed areas on the photo. In terms of the landscape, what topographic feature or landform have the developed areas been built on? The boundary between developed and non-developed areas on the photo is quite abrupt. In terms of the landscape, the developed areas have been built on flat, low-lying terrain. c) Describe the basic reason why people preferentially chose to build on the type of landform. you listed above. People preferentially choose to build on low-lying terrain due to several reasons. Firstly, low-lying landforms often provide easier access to water sources such as rivers, lakes, or underground aquifers, which are essential for human settlements. Additionally, these areas tend to have fertile soil, making them suitable for agriculture and supporting livelihoods. Moreover, low-lying terrains are often more sheltered from extreme weather conditions, such as strong winds or storms, compared to higher elevations. Lastly, the relatively flat topography of low-lying landforms makes it easier to construct infrastructure and buildings, facilitating development and urbanization. 3) What type of geologic hazards do you think might exist in the developed areas? Explain. In developed areas, there are several types of geologic hazards that can pose risks to the population. These hazards include earthquakes, landslides, and sinkholes. Earthquakes occur when there is a sudden release of energy in the Earth's crust, resulting in ground shaking. Landslides can occur when there is a slope failure due to factors such as heavy rainfall or

human activities. Sinkholes are depressions in the ground that can form when underground water dissolves soluble rocks, causing the surface to collapse. These geologic hazards can lead to property damage, infrastructure disruption, and potential loss of life. It is important for local authorities and residents to be aware of these hazards and take appropriate measures to mitigate their impacts. 4) Based on what you know about plate tectonics and the fact that the Hawaiian Islands are located in the middle of the Pacific Ocean, what type of tectonic-related hazard might the Hawaiian coastline be subjected to? Explain. The Hawaiian coastline may be subjected to volcanic hazards due to its location on the Pacific Plate, which is part of the Ring of Fire. This area is prone to volcanic activity, and the Hawaiian Islands themselves were formed by volcanic eruptions. As the Pacific Plate moves over a hot spot in the Earth's mantle, it causes the formation of new volcanoes, such as the active Kilauea and Mauna Loa. These volcanoes can pose hazards such as lava flows, ashfall, and toxic gas emissions, which can impact the surrounding coastal areas. It is important for residents and visitors to be aware of these potential hazards and follow the guidance of local authorities to ensure their safety.

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67 Figure 7.2 - Hanauma Bay on the Hawaiian island of Oahu (Courtesy of NASA) Ex 7 – Coastal Hazards

5) Figure 7.3 shows a coastal city in Indonesia that was completely obliterated by the 2004 tsunami. This tsunami was generated by a magnitude 9.1 earthquake that formed in the nearby subduction zone. The massive waves killed nearly 250,000 people in various countries around the Indian Ocean. a) To get a better sense that there was once a vibrant community of people living here, use a red marker and outline the trace of the more obvious roads still visible in the photograph. b) Notice that the rugged terrain of the coastal zone is indicative of a tectonically active area. Based on the landforms that you see in the photo, explain why people would have originally chosen to build a town at this site. The rugged terrain of the coastal zone in the photo suggests a tectonically active area. People would have originally chosen to build a town here due to the benefits of coastal access for fishing and trade. Additionally, the presence of fertile land for agriculture and the scenic beauty of the coastline likely attracted settlers. However, the devastating impact of the 2004 tsunami highlights the risks associated with building in such a location. 6) When waves approach the shore and begin to drag on the seafloor, the height of the waves naturally increases a process called run-up . What is it about the shoreline in Figure 7.3 that would have magnified the run-up of the tsunami waves as they approached shore? The shoreline in Figure 7.3 likely magnified the run-up of the tsunami waves due to its shape, slope, and topography. 7) It is quite clear that the coastal strip in this photo is extremely vulnerable to tsunami waves. Explain then why people would live and work in such a hazardous area? The coastal strip in the photo is indeed highly susceptible to tsunami waves. However, people choose to live and work in this hazardous area due to various reasons such as economic opportunities, cultural significance, and historical ties to the region. Additionally, some individuals may not have the means or resources to relocate to safer areas. While the risks are evident, it is important to consider the complex factors that influence people's decisions to reside in vulnerable coastal regions. 8) Describe two preventative steps that could be taken to minimize the loss of life should another tsunami strike this region.

Two preventative steps that could be taken to minimize the loss of life in the event of another tsunami striking the Coastal community near Aceh, Indonesia, are implementing early warning systems and constructing tsunami-resistant buildings. Early warning systems would provide timely alerts to residents, allowing them to evacuate to higher ground before the tsunami hits. Constructing tsunami-resistant buildings would ensure that structures can withstand the force of a tsunami, providing a haven for residents who are unable to evacuate in time. These measures would significantly reduce the potential loss of life and contribute to the overall safety and resilience of the community. Figure 7.3 – Coastal community near Aceh, Indonesia, that was obliterated by the 2004 tsunami (Courtesy of U.S. Navy, Tyler J. Clements). Ex 7 – Coastal Hazards 9) The before and after photos from 2008 in Figure 7.4 show the effects of Hurricane Ike on the developed portions of the barrier islands along the Texas Gulf coast. In contrast to the previous photos, the U.S. coastline along the Gulf of Mexico has been tectonically inactive for millions of years. a) What evidence do you see in the photograph that indicates this area is tectonically inactive? In the photograph of the Coastal community near Aceh, Indonesia, which was obliterated by the 2004 tsunami, evidence of tectonic inactivity can be seen due to no signs of housing or human life. b) Explain the effect your previous answer would have on the amount of development that can occur along a coastline. The previous answer would greatly impact the amount of development along a coastline.

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My previous answer would have a significant impact on the amount of development that can occur along a coastline. By implementing strict regulations and guidelines, such as limiting construction in environmentally sensitive areas and promoting sustainable practices, the potential for unchecked development and its negative consequences, such as habitat destruction and increased vulnerability to natural disasters, would be greatly reduced. This would ensure that development along the coastline is carried out responsibly and sustainably, balancing the needs of economic growth with the preservation of the coastal ecosystem. 10) The homes in the photos in Figure 7.4 were destroyed during a major hurricane, named Ike, in 2008. How can you tell from the photos that the homes where destroyed primarily by storm surge, not high winds? From the photos in Figure 7.4, it is evident that the homes were primarily destroyed by storm surge rather than high winds. The key indicators are the extensive water damage and debris scattered around the homes. The force of the storm surge is evident from the water lines on the walls and the presence of mud and sediment inside the houses. Additionally, the structural damage to the homes appears to be consistent with the impact of a large volume of water, such as collapsed walls and shifted foundations. These observations suggest that the destruction was primarily caused by the powerful force of the storm surge associated with Hurricane Ike in 2008. 11) Zoom in on the pre-hurricane (Sept. 9) photo and take a closer look at the homes right along the beach. Describe the building design used in the construction of these homes whose purpose was to protect the structures from storm surge. Upon closer examination of the pre-hurricane (Sept. 9) photo, it is evident that the homes along the beach were constructed with a specific building design aimed at safeguarding the structures from storm surge. The design features include elevated foundations, reinforced walls, and impact-resistant windows. These measures are intended to mitigate the potential damage caused by high tides and strong winds during a hurricane. The elevated foundations help to elevate the homes above the anticipated storm surge level, reducing the risk of flood damage. The reinforced walls provide additional structural strength to withstand the force of the storm, while the impact- resistant windows are designed to withstand the impact of flying debris. Overall, the building design of these homes demonstrates a clear focus on protecting the structures from the destructive forces of a hurricane.

12) Clearly, the building design in question failed to protect the overwhelming majority of homes in these photos. Provide an explanation as to why the design failed in this case. 13) Note the red arrows that have been added to the photos. Use the zoom tool to take a closer look at the area around the red arrow in which the house was destroyed. a) In addition to the house being gone, how has the land physically changed in this area? b) The physical changes you described above are indicative of an important shoreline process. What is the name of this process?

71 Figure 7.4 – Bolivar Peninsula near Galveston Bay, Texas (Courtesy USGS). Ex 7 – Coastal Hazards Part II – Shoreline Retreat The map in Figure 7.5 shows the barrier island complex located along the coast of Ocean City, Maryland. Note the solid line that shows just a single barrier island in 1933. The Ocean City Inlet seen today formed when the island was over-washed during a major hurricane in 1933. As the storm surge flowed back out to sea, it eroded a channel that cut the island in two. The island to the north is now called Fenwick and the one to south is called Assateague . Because the newly formed inlet gave people on the mainland valuable access to the open

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ocean, the U.S. Army Corps of Engineers constructed a pair of jetties on each side of the inlet. With the jetties in place, a navigation channel could be kept open. In a relatively short period sand filled in behind the northern jetty on Fenwick Island. Meanwhile, the southern island, Assateague, began to migrate toward the mainland. Note that the southern jetty, labeled “seawall” on the map, now sits in open water. 14) In what compass direction is the longshore current along this part of the coastline? Explain how you know (hint: look at the width of the beach in front of the islands). The direction of the compass is along part of the coastline going from south to north. The coastline is visible on the map with parts of the ocean surrounding and pushing up against the mainland and the islands. 15) Describe the general process by which barrier islands retreat (i.e., migrate) toward the mainland. Barrier islands located along the coast of Ocean City, Maryland retreat, or migrate, towards the mainland through a general process. This process involves various natural factors, such as wave action, tidal currents, and wind patterns. Over time, these forces cause erosion on the seaward side of the barrier island, resulting in the gradual movement of sand and sediment towards the mainland. As the sand and sediment are transported, the barrier island shifts and migrates landward. This retreat can occur over a long period of time, with the barrier island slowly moving closer to the mainland. It is important to note that this process is natural and part of the dynamic nature of coastal environments. 16) Note on the map that the position of Fenwick Island has changed very little since the 1933 hurricane, whereas Assateague Island has retreated landward a significant distance. Describe the basic reason why Assateague Island is experiencing rapid retreat while Fenwick Island appears to be rather stable. Assateague Island is experiencing rapid retreat due to a combination of factors such as erosion, sea level rise, and storm events. The island is composed of sand and sediment, which makes it highly susceptible to erosion caused by wave action and tidal currents. Additionally, sea level rise exacerbates the erosion process by increasing the amount of water that reaches the island's shoreline. Moreover, storm events, such as the 1933 hurricane, can cause significant damage and further contribute to the retreat of Assateague Island. In contrast, Fenwick Island is relatively stable due to its geologic composition, which consists of more resistant materials such as sandstone and quartzite. These factors, combined with its location further inland, contribute to the island's limited change in position over time.

Figure 7.5 - (USGS Ocean City, MD, Quadra [ 17) Because the map in Figure 7.5 was last updated (photo-revised) in 1972, this means that we know the position of the islands in both 1933 and 1972. For points X and Y,

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determine the number of feet that Assateague Island has retreated landward from 1933 to 1972. distance between X and X : on the map using the 0 to 1-mile bar “X to X” is about half a mile from each other distance between Y and Y' On the map it’s about a half Km or 0.31 miles a part 18) First calculate the retreat rate (i.e., velocity) in feet per year at both points X and Y, and then average your results. Remember that velocity equals distance divided by time. retreat rate at X: - 1933 = 1.69 - 1972 = 4.016 retreat rate at Y: - 1933 = 1.69 - 1972 = 0.803 average retreat rate: X = 2.326 Y =0.887 19) Using the average rate of retreat, predict the number of years it will take for the landward side of Assateague Island at point Z to reach the shore at point Z'. Again, use the formula of velocity equals distance over time. distance between Z and Z' = half of a km or 0.3106856 in a mile. travel time at Z: 1.575 miles in 1972. 20) Based on the number of years you calculated above, determine what year (e.g., 1999) Assateague Island should have reached the mainland, sealing off Sinepuxent Bay. Based on the number of years you calculated, it can be determined that Assateague Island should have reached the mainland, effectively sealing off Sinepuxent Bay, in a specific year. This

significant event would have had a profound impact on the landscape and ecology of the area. The natural barrier formed by Assateague Island would have created a distinct separation between Sinepuxent Bay and the surrounding landmass, potentially altering water flow patterns and influencing the distribution of plant and animal species. Understanding the timeline of this process provides valuable insights into the dynamic nature of coastal environments. 21) If you traveled to Ocean City today, you would see that Assateague Island has not yet sealed off the bay. Explain why your prediction was off. My prediction on the sealing off of Assateague Island’s Bay in Ocean City was incorrect because it seems that the necessary measures have not been implemented as anticipated. This discrepancy could be attributed to a variety of factors, such as delays in the execution of the plan or changes in the circumstances that prompted the sealing off. It is crucial to acknowledge that predictions are not always foolproof and can be influenced by unforeseen variables. Part II – Sea-Level Rise and Global Warming As described more thoroughly in Chapter 16 of the textbook, Earth's climate system is very complex and has changed continuously over geologic time. As the average global temperature changes, so too does the amount of glacial ice store on the planet's landmasses. During cool (glacial) periods, sea level falls as additional water is removed from the oceans and stored as glacial ice. Sea level then rises when the climate enters a warm (interglacial) period, and the ice begins to melt. As shown in Figure 7.6, around 20,000 years ago during the depths of the last ice age, sea level was approximately 460 feet (140 m) lower than today. Of course, whenever sea level changes, so too does the position of the shoreline. Shorelines naturally advance (shift seaward) when the sea level falls, then retreat (shift landward) as the sea level rises. Figure 7.6 - Graph showing dramatic changes in sea level during the previous glacial and interglacial periods. (Data from K. Lambeck and J. Chappell, 2002, and K. Lambeck, Y. Yokoyama, and A. Purcell, 2002)

Because climate change is not unusual in terms of Earth’s history, there is nothing really special about the position of today's shoreline which humans have grown accustomed to. Although the climate system has been relatively stable for the past 10,000 years, the sea level has continued to slowly rise as the climate moved from an ice age to the current interglacial period. For example, the amount of sea-level rise from 1900 to 2000 was only 0.6 feet (0.2 m). One of the major concerns about global warming today is that sea-level rise is accelerating due to the rapid melting of glacial ice and the thermal expansion of the oceans. If all of the remaining ice were to melt, the sea level would rise an additional 260 feet (80 m). Currently, the worst-case scenario predicted by climate scientists is a 33-foot (10 m) rise over the course of a few centuries. Were this to occur, major population centers around the world would be inundated, creating a human catastrophe of unprecedented proportions. In order to get a better sense of the potential problems associated with accelerated sea level rise, we will examine the projected shoreline changes for southern Florida shown in Figure 7.7. Note that the changes here represent the worst-case scenario of a 33-foot (10 m) rise in sea level over a several hundred-year period. 22) With the aid of a Florida road map, plot the location of the following cities on Figure 7.7B. Miami Fort Myers Tampa Cape Canaveral 23) Supposing that the sea-level rise would be slow enough so that people and businesses could be moved inland, describe some of the problems that such a move would entail. 140 0 20 40 80 100 120 60 Thousands o f yearsbe forepresent -500 -400 -300 -200 -100 0 100 Sea level compared to present feet ( ) -150 -100 -50 0 ( meters ) today previous glacial previous interglacial

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Moving people and businesses inland in response to slow sea-level rise would indeed come with its fair share of challenges. One of the main problems that such a move would entail is the massive financial burden it would impose on both individuals and businesses. The cost of relocating entire communities, constructing new infrastructure, and ensuring access to basic amenities would be astronomical. Additionally, the displacement of communities from coastal areas would disrupt established social networks and lead to a loss of cultural identity. Furthermore, moving inland could also result in strained resources and increased competition for land, water, and other essential resources. 24) Under the worst-case scenario cities around the world would be facing the same problems you described. How would the fact that this would be a worldwide problem affect society's ability to adjust to a major rise in sea level? The fact that a major rise in sea level would be a worldwide problem would significantly impact society's ability to adapt and respond effectively. Cities across the globe would be grappling with similar challenges, such as coastal erosion, flooding, and loss of infrastructure. This shared experience would necessitate international cooperation and collaboration to develop comprehensive strategies and solutions to mitigate the effects of rising sea levels on a global scale. Figure 7.7 –Relief map of southern Florida showing the shoreline change associated with a 33foot (10 m) sea-level rise. (Courtesy of NASA)

A) B) Miami Fort Myers Tampa Cape Canaveral

Lab 7 GEO

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