The relative movements of tectonic plates

Transcription

1 The relative movements of tectonic plates can be used to explain the formation and location of many geologic features at the Earth s surface, such as earthquakes, volcanoes, mountains, hot spots, and oceanic ridges. Convergent boundaries occur where one plate moves underneath another and cause earthquakes and the formation of volcanoes on the overriding plate. Divergent boundaries occur where two plates are spreading apart from each other, commonly seen in the ocean accompanied by the formation of new oceanic crust. Transform boundaries occur where plates are sliding past one another and form fracture zones. In the Earthscience curriculum, plate tectonics provides an important context that is used to explain both topography and geohazards. by Jill Burrows, Alec Bodzin, David Anastasio, Dork Sahagian, Denise Bressler, Lori Cirucci, Scott Rutzmoser, and Allison Teletzke December

2 FIGURE 1 The web GIS displaying the seismic-hazard (solid green through red background pattern), volcanoes (colored triangles), historical-earthquakes (red circles), and plate-boundary layers. The distance measurement (blue line) between Bethlehem, Pennsylvania (blue circle), and the location of the nearest historical earthquake with a magnitude greater than 8.0 is shown on the map. This article describes a series of six tectonics investigations we developed to enhance the middle school Earth-science curriculum. These investigations include spatially enabled learning technologies that use freely available web GIS, which is compatible with any desktop computer, laptop, or mobile device, including tablets such as the Apple ipad. Web GIS is a visualization tool in the form of web-based application software that can be used to store, retrieve, and manipulate georeferenced scientific data. Students can use web GIS to view and explore data entirely online (Kulo et al. 2013). Studies have shown that the use of spatial technologies such as GIS in the classroom can improve students analysis and spatial-thinking skills and increase understanding of the material being covered (Baker and White 2003; Demirci 2008; Bodzin and Cirucci 2009). The web GIS investigations can be accessed for free at Computers or tablets with internet connections are the only materials needed to complete the investigations. Students can work individually or, depending on computer availability, in groups of two or three. Four of the investigations (1, 2, 3, and 5) can be completed in one 45-minute class period, and two investigations (4 and 6) can be completed in two class periods. The investigations instructional materials have been effectively used in eighth-grade classrooms with students of varied ability levels, including English language learners. The website includes a series of support materials designed to assist with classroom implementation detailed teacher guides, video tutorials, content background materials, and assessments for each investigation. 30

3 FIGURE 2 An example of the outlined boundary of the North American and Juan de Fuca plates with the volcanoes (colored triangles) and earthquakes (yellow circles) layers displayed (To access the assessments, use login eliteacher and password 87dja92.) In addition to the six investigations described below, there is a web GIS for open-ended investigations that students can use to answer their own questions about tectonics or that can be implemented with teacher-provided guiding questions for students to further explore additional geospatial relationships and patterns in tectonics data. The investigations are aligned to the disciplinary core idea Earth and Space Science from A Framework for K 12 Science Education (NRC 2012), with a primary focus on core idea ESS2.B: Plate Tectonics and Large-Scale System Interactions. The investigations also incorporate crosscutting concepts, including Cause and Effect; Scale, Proportion, and Quantity; and Energy and Matter. Cause and Effect is a common thread throughout the tectonics investigations. The plate-tectonic causes of earthquakes and volcanoes are placed in the context of their effects in terms of natural hazards. Scale, Proportion, and Quantity are key aspects of tectonics using our GIS-based approach. Learners delve into scale and proportion issues with map zoom in various activities and use quantitative means to assess the relative motions of tectonic plates. The crosscutting concept of Energy and Matter is integral to the tectonics learning material, in which the relation between plate motions (kinematics) and forces (dynamics) results in interactions that release energy in the form of earthquakes and volcanoes. Each investigation uses a series of design principles to promote geospatial thinking and includes motivating entry points to engage learners, personally relevant and meaningful examples, and learning activities that apply to diverse geographical contexts. Investigation 1: Geohazards and me: What geologic hazards exist near me? Which plate boundary is closest to me? In this investigation, students use the web GIS to locate geologic hazards created by tectonic forces near their geographic location. They discover where the most recent earthquake and volcano occurred nearest to their location, investigate how geologic hazards are distributed on the Earth s surface, and infer how this distribution is related to plate tectonics. (See also Bringing Earthquake Engineering to Your Hometown in this issue.) Students first use the Find Locations tool to place their current location on their map. With their loca- December

4 FIGURE 3 An example of the swipe tool in investigation 3 where the surface-heat-flow layer (left portion of the figure) is being swiped past the age-of-the-ocean-floor layer (right portion of the figure) tion on the map, students then display a series of data layers, including historical earthquakes, volcanoes, and plate boundaries, to observe and measure the hazards and plate-boundary locations that are closest to where they live. Students can learn about individual earthquakes and volcanoes by clicking on them to display a pop-up data box that includes a link to additional information on the U.S. Geological Survey, National Oceanic and Atmospheric Administration, or Smithsonian website. They then learn that geologists determine seismic hazards by studying the timing, location, and magnitude of past earthquake events and use this information to develop risk-assessment maps that communicate the potential for seismic hazards to occur in a particular area. Figure 1 shows the seismichazard layer displayed on the web GIS. The darkergreen color in the seismic-hazard layer on the U.S. East Coast is associated with a lower seismic-hazard risk. The yellow, orange, and red colors displayed in the seismic-hazard layer, such as those on the West Coast, are associated with a higher seismic-hazard risk. Using the web GIS, students are able to observe that the highest-risk areas correspond to the locations of more volcanoes and earthquakes. Investigation 2: How do we recognize plate boundaries? In this learning activity, students identify the eastern and western boundaries of the North American plate by analyzing the tectonics data in the web GIS. They examine earthquake-epicenter and volcano data to outline the plate boundaries. In addition, the movements of the surrounding plates are studied to determine the plate-boundary types (divergent, convergent, or transform) at different locations. This learning activity also addresses a common misconception that convergent-plate-boundary volcanoes are found exactly on plate boundaries rather than on the overriding plate at a distance from the boundary, which depends on the dip of the subducting slab. Students first display the locations of earthquakes and use the web GIS draw tools to outline the location of the North American plate boundary. Next, they use the web GIS to identify the adjacent plates next to the North American plate. They then activate the volcanoes layer and outline the Juan de Fuca plate by drawing a line to the west of the volcanoes located in the northwestern U.S and western Canada (see Figure 2). The web GIS is then used to examine the 32

5 FIGURE 4 An elevation profile drawn using the elevation-profile tool. The light-blue dot on the profile line corresponds to the vertical light-blue line on the elevation-profile graph. relative plate motion across the plate boundaries students have drawn to identify divergent, convergent, and transform boundary areas. In the last part of this investigation, students use the web GIS to identify different types of lithosphere. They learn that oceanic lithosphere is associated with oceanic crust and exists beneath ocean basins and that continental lithosphere is associated with continental crust and exists beneath continents. Investigation 3: How does thermal energy move around the Earth? In this investigation, students determine where heat is able to escape from the Earth s interior. They investigate the distribution of surface heat flow around the Earth and how this is related to plate boundaries. They also discover which geologic features on the Earth s surface are associated with heat loss from the Earth s interior. While these ideas may be difficult for students to understand with typical print-based materials, the web GIS enables them to understand these complex ideas through the use of manipulating georeferenced data sets. Using the web GIS, students can dynamically visualize how the distribution of hot spots on the Earth s surface is spatially related to lithosphere thickness, plate motion, and heat flow. Students begin this investigation by discovering the relationship between heat flow and plate boundaries. Using the web GIS data, they observe that the highest surface heat flow is along divergent plate boundaries. Students use the swipe tool (see Figure 3) to discover the relationship between surface heat flow and the age of the ocean floor. Using the swipe tool, students can move one data layer over another to analyze the geospatial patterns displayed in the web GIS. The surfaceheat-flow layer displayed on the left side of Figure 3 reinforces the concept that oceans are hotter than continents. Toward the figure s center, at the swipe seam, the correlation of heat flow and the age of the ocean December

6 floor is quite evident; we emphasize to students that younger crust is hotter and older crust is colder. On the right side of the figure, students can easily visualize the age of the ocean floor increasing as the floor moves continent-ward from the mid-ocean ridge. Students use the elevation-profile tool to discover that ocean bathymetry is related to both surface heat flow and the age of the ocean floor. The elevation-profile tool allows students to create an elevation profile of an area of the map by drawing a line across that area (Figure 4). The elevation-profile tool simultaneously displays the elevation of a specific point on the map and that point in the corresponding map profile. In the investigation, students learn that younger ocean floor is warmer and therefore more buoyant and sits at higher elevations. As the ocean floor cools and spreads away from the divergent boundary, it sinks and decreases in elevation. In the last part of this investigation, students learn about surface heat flow near hot spots. They identify which plates have the most hot spots and learn how lithosphere thickness and plate speed affect hot-spot abundance by examining the distribution of hot-spot locations and plate-movement vectors. Investigation 4: What happens when plates diverge? In this investigation, students locate and study different divergent boundaries using web GIS. Divergent boundaries occur where two plates are spreading apart from one another and result in the formation of new oceanic crust, shallow earthquakes, and the most voluminous volcanoes on Earth. Students investigate how tectonic stresses are accommodated at the plate boundary by examining earthquake and fault data FIGURE 5 Screenshot showing the North American and African continent boundaries aligned with the 90-million-year age position. The continent-boundaries tool is activated highlighting the North American and African continents. The age-of-the-ocean-floor layer is displayed. 34

7 and calculating the half-spreading rate of a plate boundary. In addition, they use web GIS to investigate features of passive margins and compare a young divergent boundary to an old divergent boundary that has spread and resulted in a passive margin. Students begin this investigation by discovering the relationship between earthquakes and divergent boundaries. Students perform a series of data queries to discover the patterns of different earthquake depths along different plate-boundary types. Using the web GIS, students discover that earthquakes do not occur at great depths, because the lithosphere is too thin and too hot for earthquakes to happen at those locations. Next, students calculate the half-spreading rate of a divergent plate boundary and discover how passive margins form by looking at variations in the marine-gravity-anomaly layer. The marine-gravityanomaly layer indicates different densities in oceanic crust compared to continental crust and provides a geospatial visualization to help learners understand how continental crust transitions to oceanic crust at a passive continental margin. To conclude the investigation, students use the continent-boundaries tool to simulate the movement of the North American and African continents from the Mid-Atlantic Ridge to their locations 90 million years ago to observe ocean-floor spreading and the formation of passive margins along the coasts of these two continents. Students first place the continents at the Mid-Atlantic Ridge and then, using the map legend for the age-of-the-ocean-floor layer, determine and place the continents at the location where they were positioned approximately 90 million years ago (Figure 5). Students can click on the outline of each continent to drag and rotate it to simulate its historical location. FIGURE 6 Investigation 5: What happens when plates move sideways past each other? In this investigation, students study the history of oceanic transform boundaries using earthquake and age-of-the-ocean-floor data. They then investigate the continental transform boundary at the San Andreas fault zone and view historical photographs embedded in the web GIS and earthquake data to learn about the seismic hazards associated with living on a continental transform boundary. The Charlie-Gibbs fracture zone with arrows showing the direction the plates are moving. Deep transform earthquake epicenters (yellow circles), plate boundaries, and the age-of-theocean-floor data layer are displayed. Students begin this investigation by exploring an oceanic transform boundary at the Charlie-Gibbs fracture zone. They use the query-earthquakes tool to determine the relationships between earthquakes and different plate boundaries. The query-earthquakes tool allows students to specify an earthquake depth (all depths, greater than 100 km, between 10 and 100 km, or less than 10 km) and type (extensional, contractional, or transform) and then display the results on their map. Students learn that transform earthquakes occur on transform faults and are typically greater than 100 km deep. Extensional earthquakes are found on divergent boundaries and are shallow (less than 10 km deep). Students can learn more about each earthquake by clicking on it in the web GIS; a pop-up data box display appears with additional information, including the date the earthquake occurred, its magnitude, and its focal depth. Students also learn that volcanoes do not occur along transform boundaries because subduction is not taking place. Embedded videos within the web GIS are used to help students understand the different plate motions that occur at divergent and transform boundaries. Figure 6 illustrates how students are able to distinguish a transform plate boundary in a fracture zone. The arrows show the direction the plates are moving, and the query-earthquakes tool is used to show only deep earthquakes that occur on transform faults. To conclude the investigation, students examine a continental transform boundary at the San Andreas fault zone. They examine GPS plate vector data and em- December

8 FIGURE 7 The subduction-zone profile tool displays for the Kodiak Island and Atka Island subduction zones with surface elevation above sea level (light-blue circles), earthquakes (red circles), volcanoes (purple triangles), and subducting slab depth (gray circles) displayed. bedded videos to understand the dynamic plate motion in the fault zone. Next, they examine population density, seismic-hazard data, historical earthquake epicenters, and historical images to understand the risks involved with living in this area. Investigation 6: What happens when plates collide? In this investigation, students use the distribution of earthquakes and volcanoes in web GIS to learn about plate collisions at an ocean-ocean subduction zone and an ocean-continent subduction zone. They discover the relationship between the subduction zones and volcanoes, and determine the slope of a subducting slab along a convergent plate boundary. Students also learn about the types of landforms created by continents colliding at convergent zones. Students begin this investigation by learning about plate collision in the Aleutian Islands, Alaska, at an ocean-ocean subduction zone and at an ocean-continent subduction zone by analyzing the earthquakes and volcanoes data in the web GIS. Students compare two subduction-zone profiles that display the depthto-slab location and earthquakes and volcanoes layers at two locations (see Figure 7): one where ocean crust is subducting underneath continental crust (O\C Kodiak Island) and one where ocean crust is subducting underneath ocean crust (O\O Atka Island). Using the subduction-zone profile tool, students can identify on which plates the deep earthquakes occur and on which plate they see volcanoes at the surface. This tool provides students with an interactive visualization in the web GIS. When students place their cursor over the profile line on the map, they see the corresponding point on the subduction-zone profile display. In the investigation, students analyze these two profiles and observe that the angle of the subducting slab is steeper where ocean is subducting underneath ocean than where ocean is subducting underneath continent. To conclude the investigation, students recreate a continent collision between North America and Africa to learn about convergent zones and how the Appalachian Mountains were formed. 36

9 Conclusion Web GIS can be used to promote geospatial thinking by enabling powerful data visualizations and enhancing Earth-science learning in middle school classrooms. This series of six authentic tectonic investigations was designed to enhance existing middle school Earthscience curricula. We developed and implemented a tectonics content assessment designed to measure knowledge of important tectonics concepts in addition to geospatial thinking and reasoning skills applied to tectonics. The assessment is available at edu/eli/tectonics. (To access the assessments, use login eliteacher and password 87dja92.) Results from a pilot study implementing these investigations in middle school science classes found that students who used these investigations had better content-knowledge gains in addition to better geospatial thinking and reasoning skills applied to tectonics than students who did not use these investigations as part of their Earth-science curriculum. When geospatial technologies such as web GIS are used to teach and learn Earth science, middle school students can not only enhance their understanding of important tectonics concepts but also improve important geospatial thinking and reasoning skills. n Acknowledgment This material is based upon work supported by the National Science Foundation under grant #DRL Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. References Baker, T.R., and S.H. White The effects of G.I.S. on students attitudes, self-efficacy, and achievement in middle school science classrooms. Journal of Geography 102 (6): Bodzin, A.M., and L. Cirucci Integrating geospatial technologies to examine urban land use change: A design partnership. Journal of Geography 108 (4 5): Demirci, A Evaluating the implementation and effectiveness of GIS-based application in secondary school geography lessons. American Journal of Applied Sciences 5 (3): Kulo, V., A. Bodzin, R. McKeon, L. Cirucci, D. Anastasio, D. Sahagian, and T. Peffer The Isle of Navitas: Planning for energy use with web GIS. Science Scope 36 (6): National Research Council (NRC) A framework for K 12 science education: Practices, crosscutting concepts, and core ideas. Washington, DC: National Academies Press. Jill Burrows (jillerinburrows@gmail.com) is a doctoral student in the Department of Earth and Environmental Sciences, Alec Bodzin is an associate professor in the Teaching, Learning, and Technology Program, David Anastasio and Dork Sahagian are professors in the Department of Earth and Environmental Sciences, and Denise Bressler is a doctoral student in the Department of Education and Human Services, all at Lehigh University in Bethlehem, Pennsylvania. Lori Cirucci is an eighth-grade teacher at Broughal Middle School in Bethlehem, Pennsylvania. Scott Rutzmoser is a computer consultant at Lehigh University. Allison Teletzke is a graduate of the Department of Earth and Environmental Sciences at Lehigh University and now works at the Chevron Energy Technology Company in Houston, Texas. December