Chapter 8 - Chapter 8 Due 11:59pm on Friday To understand...

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Unformatted text preview: Chapter 8 Due: 11:59pm on Friday, February 27, 2015 To understand how points are awarded, read the Grading Policy for this assignment. Give It Some Thought: Sand Movement on the Beach Ocean waves are actually energy moving across the surface of the water. This movement is not individual water particles moving, but the energy of storms or wind. As waves move, they pass their energy between water particles by orbital, or circular, motion where the particle moves in a circle that brings it back to its original place. When waveforms are in deep water, they do not “feel” the ocean bottom and are unaffected by water depth. As waves approach the shore, the water becomes shallower and causes the water within the wave to be affected by the ocean bottom. This slows waves in the surf zone and allows waves further out to catch up. As a result, waves grow higher as the speed and wavelength of the wave increase. When waves reach the shore, they always retreat perpendicular to the shoreline due to refraction. If waves approach a beach at an angle, they are still refracted perpendicular to the shoreline. This causes the net movement of water and sand grains to be along the shoreline. This movement of water along the shoreline is called longshore drift. Sometimes retreating waves move as surface flows instead of along the ocean bottom. These strong surface currents are called rip currents and can be very dangerous to unwary swimmers. Part A -­ The movement of a raft beyond the surf zone During a visit to the beach, you get in a small rubber raft and paddle out beyond the surf zone. Tiring, you stop and take a rest. Describe the movement of your raft beyond the surf zone. Select all that apply. You did not open hints for this part. ANSWER: The raft moves up and down vigorously due to the breaking of taller waves compared to the surf zone. The raft moves in a circle, and it returns to essentially the same place. The raft will move toward shore along with the water particles underneath. The raft’s net movement is not toward the shore compared to the surf zone. Now, let's look at how waves move sand along the beach face as they reach shore. Part B -­ Sand movement on the beach Wave action creates and changes beaches drastically. The image below shows the movement of water and sand along a beach. Drag the appropriate labels to their respective targets. Note that some labels may not go with any target. You did not open hints for this part. ANSWER: Now, let's look at a hypothetical scenario to investigate further how waves move sand along the beach. Part C -­ The surf zone While you are playing Frisbee in the surf zone with another person, your friend watches while sitting on the beach nearby. After a while, you look up at the beach and realize you are no longer directly in front of your friend, who remained stationary on the beach all the while—you are still in the surf zone, but 30-­40 yards from where you started. What is the correct reason for this movement? You did not open hints for this part. ANSWER: Waves were coming in to the shore straight on so the current carried you upstream. Waves were coming at the shore at an angle. The longshore current moved downstream to that angle and pushed the Frisbee players that direction. The beach moved opposite the angle of the waves. One person must have continually overshot the Frisbee to move them further out to sea. Interactive Animation: Tsunami When you have finished, answer the questions. Part A How are tsunamis generated? ANSWER: through creation of the seafloor above water through creation of the seafloor under water through displacement of the seafloor above water through displacement of the seafloor under water Part B What is a tsunami? ANSWER: a series of water waves that travel away from a fault in all directions at high speed a series of water waves that travel toward a fault in all directions at low speed a series of water waves that travel toward a fault in all directions at high speed a series of water waves that travel away from a fault in all directions at low speed Part C Why do ships at sea tend not to notice tsunamis? ANSWER: Tsunamis in deep water have small wave height and long wavelength. Tsunamis in deep water have small wave height and short wavelength. Tsunamis in deep water have large wave height and short wavelength. Tsunamis in deep water have large wave height and long wavelength. Part D Why does the wave height of a tsunami increase as the tsunami enters shallow water? ANSWER: In shallow water, the energy of the tsunami must be contained within a larger water column. In shallow water, the energy of the tsunami must be contained within a smaller water column. In shallow water, the wind driving the tsunami must push a smaller water column. In shallow water, the wind driving the tsunami must push a larger water column. Part E What type of plate boundary are most tsunamis associated with? ANSWER: convergent plate boundaries divergent plate boundaries transform plate boundaries Part F Which ocean is associated with most tsunamis? ANSWER: Indian Ocean Atlantic Ocean Pacific Ocean Arctic Ocean Part G Will Sumatra experience another tsunami like the destructive one of December 2004? ANSWER: This is unlikely, because Sumatra is near many ocean trenches. This is likely, because Sumatra is near many ocean trenches. This is unlikely, because Sumatra is in the Pacific Ocean. This is likely, because Sumatra is in the Pacific Ocean. Encounter Earth: Tohoku Earthquake Part II This Exploration will help you visualize and investigate key topics using Google Earth™. 1. Open the Google Earth ™ .kmz file for this item. 2. In the Places panel on the left, expand the Temporary Places folder. 3. Return to this Mastering screen and follow the instructions in the yellow on the right. Having trouble navigating this Exploration in Google Earth? Visit the Help section. Don’t have Google Earth yet? Download and install the latest version of Google Earth here. Introduction: The island country of Japan rides atop and is rooted to the eastward-­moving Okhotsk plate, an extension of the North American tectonic plate. Just 120 km east of Japan, along the deep-­ocean Japan Trench, the Pacific plate moves westward at more than 9 cm/yr and begins its dive down and under the Okhotsk plate. The motion is not smooth, and huge stresses build up and are stored in the rocks as the colliding plates lock up against each other. On 11 March, 2011, rocks along the boundary 100 km east of northern Japan ruptured in a sudden and catastrophic release of years of built-­up stress, triggering a magnitude 9 earthquake—the largest ever recorded near Japan, and the fifth largest ever recorded anywhere on Earth. In less than 2 minutes, literally hundreds of thousands of cubic miles of rock bent, stretched, and moved as much as 24 meters! Most of the adjustment occurred in the overriding Okhotsk plate, moving, shaking, and altering the size and shape of the Pacific seafloor and the nearby island of Japan. One of the most devastating effects of the sudden deformation of the seafloor was the generation of a massive tsunami that overran the eastern shore of northern Japan just minutes after the quake occurred. In this investigation, you will look at some of the data collected during the quake in an effort to understand and quantify some of the changes observed in the minutes and days following the quake. By the end of this Investigation, you should be able to: Interpret various forms of earthquake slip maps. Measure, calculate, and describe the various motions and adjustments of the bedrock involved in the Tohoku earthquake. Instructions for all Parts: 1. Make sure you have opened the KMZ file from the blue box on the left. 2. In the Places panel, expand the Tohoku Earthquake.kmz folder. Instructions for Parts A-D: 1. In the Places panel, double-click the ? Tohoku Quake of 11 March, 2011 placemark to fly to northern Japan. 2. The red + placemark off the east coast of Japan marks the approximate epicenter of the quake. Clicking on it in the 3D display will open a balloon with links to the USGS web pages containing detailed scientific information about the quake. 3. Turn off the red + placemark showing the epicenter to unclutter the 3D display by clicking the checkbox next to its name in the Places panel. 4. Double-click the Slip Models folder in the Places panel to fly to this region. This action will also expand the folder. The folder contains graphic data from Japan’s Geospatial Information Authority. 5. Turn on the Japan-Uplift-and-Subsidence overlay by checking the box next to it in the Places panel. Part A When the Tohoku earthquake occurred, as much as 30 meters of the Pacific plate was subducted westward under the Okhotsk plate, upon which sits the island nation of Japan. The crust of the Okhotsk plate directly west of the plate boundary bulged upward. In light of this, what is a possible explanation for the uplift indicated in red just west of the plate boundary? You did not open hints for this part. ANSWER: During the earthquake, a large part of the Pacific plate was thrust under the Okhotsk plate. This both lifted and deformed the edge of the Okhotsk plate. The earthquake injected a massive amount of magma into the Okhotsk plate directly west of the plate boundary, causing the plate to bulge upward. The area of uplift represents a piece of the Okhotsk plate that detached from the rest of the plate when the earthquake occurred. There appears to be uplift because the earthquake shifted great amounts of sediment into the ocean trench, effectively raising the seafloor. Part B The Tohoku earthquake generated a massive tsunami that devastated the nearby coast of Japan. In light of your answer to Part A, what is the explanation for the generation of the tsunami? You did not open hints for this part. ANSWER: The earthquake caused many landslides along the coast of Japan, depositing huge amounts of material into the ocean. Volcanism associated with the earthquake was responsible for the tsunami. The sudden lifting of the seafloor around the bulging crust pushed huge volumes of water up, out, and away in all directions. The sudden lifting of the seafloor around the bulging crust redirected ocean waves and focused them on the coast of Japan. Part C In light of your answers to Parts A through B, explain how the earthquake changed the coastline in a way that increased the destructiveness of the tsunami as it came ashore. You did not open hints for this part. ANSWER: The effective height of the tsunami would have been increased by the amount of uplift of the coastline: here, around 1 meter. The effective height of the tsunami would have been increased by the amount of subsidence of the coastline: here, around 1 meter. The effective height of the tsunami would have been decreased by the amount of uplift of the coastline: here, around 1 meter. The effective height of the tsunami would have been decreased by the amount of subsidence of the coastline: here, around 1 meter. Instructions for Part E and F: 1. Turn on the Japan-Mainshock-Slip overlay. Notice the dashed isolines on the map; they represent the depth to the plate boundary below. The green arrows represent the amount of slip at various places along the plate boundary. The white star represents the earthquake focus. Part D What is the magnitude of the maximum slip indicated here, in meters? You did not open hints for this part. ANSWER: 20 8 24 32 Part E According to this chart, in what general direction did slip occur? You did not open hints for this part. ANSWER: The motion was both downward and toward the west. The motion was both downward and toward the east. The motion was both upward and toward the west. The motion was both upward and toward the east. Instructions for Part G and H: 1. With the Japan-Mainshock-Slip overlay still turned on, in the Layers panel, open the Gallery folder, and turn on the Volcanoes layer. Part F Describe the relationship between the location of volcanoes on the island of Japan and the depth to the subducted plate below Japan. You did not open hints for this part. ANSWER: The plates appear to line up along the 100-­ kilometer dashed depth isoline, and there are more where the plate is shallower. There are no volcanoes over the plate that is more than 100 kilometer deep. The volcanoes appear to line up along the 100-­kilometer dashed depth isoline, and there are more over areas where the plate is deeper. There are no volcanoes over plate that is less than 100 kilometer deep. The volcanoes appear to be located randomly above the subducted plate. There is no pattern between the location of the volcanoes and the depth to the subducted plate. The volcanoes appear to line up along the plate boundary, and there are more over areas where the plate is more than 100 kilometer deep. Part G What might be a possible explanation for the fact that the there are no volcanoes over areas where the subducted plate is less than 100 kilometer deep? You did not open hints for this part. ANSWER: Volcanoes can develop only beneath continental crust. Oceanic crust is too dense for magma to penetrate. The crust beneath Japan is much thinner than nearby oceanic crust, making it easier for magma to rise through the asthenosphere and lithosphere to erupt at the surface. Volcanoes would develop. Magma is not generated in significant amounts until the subducted plate has reached a depth of 100 Volcanic Arc Creation. The subducted plate prevents magma from rising. The magma collects beneath the subducted plate instead of causing volcanism on the surface. When you complete this exercise, uncheck any folder in the Tohoku Quake.kmz folder. Chapter 8 Reading Quiz Question 10 Part A A disadvantage shared by wave, solar and wind energy is that ___________________________. You did not open hints for this part. ANSWER: governments are unwilling to subsidize renewable forms of energy it is not available on demand, and there currently is no viable way to store the energy the energy tends to be concentrated in areas of high latitude and is not readily available to tropical countries the power produced must be transmitted long distances from where it is produced to where it is consumed installations must be protected from the very energy that they collect Chapter 8 Understanding the Concepts 10 Part A Of the following statements about tsunami, which is/are true? You did not open hints for this part. ANSWER: If you are at a beach and the water suddenly drains out away from shore, it is safe to go explore the newly exposed land. The tsunami warning system uses seismic waves and deep-­ocean pressure sensors to detect tsunami. Tsunami are undetectable by ships in the open ocean. At the coast, a tsunami looks like a suddenly occurring high or low tide, which is why they are misnamed "tidal waves." Tsunami always express themselves at the coast as a single rapid surge of water towards the shore. Tsunami have a very long wavelength, so they travel at very high speeds (equivalent to the speed of a jet airplane). Visualizing Oceanography -­ Waves and Water Dynamics Part A The diagram below shows a perspective view of a set of waves moving to the right. Match each letter with the correct feature of a wave. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer. ANSWER: Part B On this image of a storm area, match the correct letter to each of the following items. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer. ANSWER: Part C This diagram illustrates the phenomenon of wave interference (results not shown). Correctly match the letter with each type of interference that would be produced by the overlapping of the sets of waves shown below. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer. ANSWER: Part D In this perspective view of waves approaching shore, match the correct letter to each of the following items. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer. ANSWER: Part E The map below shows global coastal wave energy resources. Using what you've learned about ocean waves, match the letters to the correct colors. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer. ANSWER: Give It Some Thought: Earthquake and Tsunami Prediction Although there is no reliable method for short-­range earthquake predictions, it is possible to assess the probability that an earthquake of a certain magnitude will occur over decades to a century in a location. This is called long-­range earthquake forecasting, and it is useful for determining the risk of an earthquake, which can help guide how buildings, dams, and roadways are constructed in the area to withstand shaking. After an earthquake occurs in or near an ocean, it is important to warn nearby coastal areas of a possible tsunami. Tsunami warning systems in the Pacific and Indian Oceans combine seismograph data with information from buoys in the open ocean. This records energy released during an earthquake and tidal gauge readings that measure the subtle changes in ocean levels that occur when a tsunami is in the open ocean. Although we cannot predict earthquakes with such accuracy, we can predict tsunamis. Part A -­ Earthquake prediction and warnings Which of the following best describes how scientists help the public prepare for an earthquake event? You did not open hints for this part. ANSWER: Scientists cannot predict when exactly an earthquake will occur, but they can identify tectonically active areas that are likely to produce earthquake activity and let the public know they are in an earthquake-­prone area. Scientists have no idea what areas might experience earthquakes in the future, so there is no way to help the public prepare. Scientists can predict when earthquakes will happen and alert the public because there are many precursors and signs that an earthquake is about to occur. Now, let’s investigate how an earthquake might affect the surrounding areas. Part B -­ Analyzing the degree of threat of an earthquake Look at the accompanying map showing the locations of the 15 largest earthquakes in the world since 1900. The information on the map makes it possible for people living around these active earthquake areas to know that they live in a high-­risk area for earthquakes. Imagine an earthquake is about to occur at location 2 on the map (southern Alaska). Which of the following statements is most accurate? Select all that apply. You did not open hints for this part. ANSWER: Most of the people living at location 2 probably are aware that they live in a location where earthquakes are likely. There are no locations on the map that could benefit from an alert that an earthquake at location 2 occurred, because they won’t feel any of the effects. Only location 2 could benefit from an alert so people can evacuate before the earthquake occurs. All locations (except 9) could benefit from an alert that an earthquake occurred at location 2, because they are near the ocean and might experience a resultant tsunami. Location 2 is not in the middle of the ocean and therefore will not produce a tsunami, so none of the locations need to be notified of the earthquake. Now, let’s investigate the impact that one of those earthquakes could have on other areas. Part C -­ Predicting a tsunami Look again at the map. Bear in mind that all the earthquake locations that are not inland are on a convergent plate boundary (subduction zone...
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