Microsoft Word - GEOG1106_Lab9_PlateTectonics.docx
Name: Date:
Plate Tectonics, Earthquakes and Volcanoes
Lab Questions
***Please submit only this document at the end of the lab period***
INSTRUCTIONS: Please read the lab reader before beginning this exercise. The following lab questions will be based upon the material given in the lab reader.
Part I: General Plate Tectonics
Based on Figure 2 of the reader, answer the following questions:
1. [2.5] What direction is the Pacific plate moving?
2. [5] What types of plate boundaries does the North American plate have?
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3. [2.5] List two plates that are creating a convergent-subduction boundary. Which of this pair of plates is the subducting plate?
4. [2.5] List two plates that are creating a convergent-collision boundary.
5. [5] Where are most of the divergent plate boundaries located: in the oceans or on continents? Where is the largest divergent continental plate boundary?
6. [2.5] Name two plates that are creating a plate boundary where you would see volcanoes. What type of plate boundary is this?
Part II: USGS Earthquake Viewer in South America
Go to https:
earthquake.usgs.gov/earthquakes/map/. You will see a map of the United States. Scroll and zoom out in the map view so that you see the entire continent of South America. In the top right corner is a symbol for settings that looks like a gear. Click on settings and under “Earthquakes,” select “30 Days, Magnitude 4.5+ U.S.” At the bottom of the map view, click on “Show Legend.”
Your map should look similar to the following screenshot:
7. [5] What do the red lines represent? What do the dots represent?
8. [2.5] What mountain range is located along the west coast of South America?
9. [5] Click on an earthquake. A little box should pop up that provides information about your selection. What 5 pieces of information are provided in this box?
10. [5] On the following figure, draw the location of the plate boundary that runs along the western edge of South America.
11. [5] Now, click on the locations of the earthquakes in the USGS mapper. Draw dots on your map to show the location of the earthquakes and write their depth
(including units) next to its location.
12. [5] Do you notice any patterns related to the depth of earthquake and its distance from the plate boundary? Describe any patterns. (Use complete sentences.)
13. [5] Using what you know about oceanic and continental crusts as well as the depth of earthquakes at plate boundaries, list what type of plate boundary is along the western edge of South America. Explain why you chose this type. (Use complete sentences.)
14. [5] Would you expect to see volcanoes along this plate boundary? If so, how do volcanoes form at this type of plate boundary?
15. [5] On your map, draw possible locations for volcanoes using upside-down V’s to represent the volcanoes.
16. [5] Move your online map so that you can see the plate boundary located to the east of South America (i.e., in the middle of the Atlantic Ocean). How does the number of earthquakes on the western plate boundary compare to the number on the eastern plate boundary? How do the depths of the earthquakes compare from one side to the other?
17. [5] What do you think is the cause of the differences in the number and depth of earthquakes?
18. [10] Complete the cross-section diagram (below) of the plate boundary along the western edge of South America. (1) Label the name of each plate, (2) draw a
ows depicting the movement of each plate, (3) draw at least 3 X’s where an earthquake focus may be, (4) draw and label the location of a volcano, and (5) draw and label where magma will form and act as the fuel for the volcano.
Part III: USGS Earthquake Viewer in the Continental United States
Move your earthquake viewer map to the Lower-48 States of the U.S. In the map settings, change the Earthquakes selection to “30 Days, Magnitude 2.5+ U.S.”
19. [5] Examining the earthquake viewer map, what states appear to have the most earthquakes?
20. [5] Using basic reasoning, what processes could explain the number of earthquakes in California? (Use complete sentences.)
21. [5] From measured data and the reader, have there always been large numbers of earthquakes in the central United States, or is this a new trend? Explain.
22. [2.5] According to the USGS, what is the cause of the increased number of earthquakes in central U.S?
Bonus Question
23. [5] Many people think that the ocean floor is deepest at diverging mid-ocean plates; however, it is deepest at trenches associated with subduction zones. A cross-section profile of a mid-ocean ridge (figure below) shows that the highest elevation for each plate is at the spreading center. Farther from the spreading center, the oceanic crust sinks. Why is the spreading center higher in elevation than the rest of the plate? [Hint: Think about temperature differences as you move away from the spreading center. How would temperature affect properties of the plate?]
Microsoft Word - GEOG1106-Lab9_PlateTectonics_Reader.docx
Reader:
Plate Tectonics, Earthquake and Volcanoes
Learning Outcomes: Many of the iconic landforms that we see across our world have been created by plate tectonic processes. Mountains, rift valleys, volcanoes, calderas, and other landscape features are explained by the theory of plate tectonics. In this lab, you will examine a few of these processes and the landscapes they form. You also will:
1. Interpret information from various types of maps and graphs.
2. Add information to a map and a diagram to better understand associated processes.
3. Learn about both natural and human-induced earthquake activity.
Materials: Pencil, lab handout, scientific article, computer with internet.
Directions
1. Complete Reading & answer questions: The reading describes some basics about plate tectonics and the associate types of plate movements. After you complete this reading, complete the associated questions in Part 1.
2. Use the USGS earthquake viewer & answer questions: In Parts 2 and 3, you will use the online earthquake viewer provided by the U.S. Geological Survey (USGS) to answer the associated questions.
3. Answer bonus question: In this lab, you have the opportunity to answer a bonus question that is worth 10 points!
Additional Resources
Scan the barcodes shown during reading section to get more information and study about the topics of this lab.
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Part I. Basics of Plate Tectonics
Earth is composed of three major layers: (1) the crust, (2) the mantle, and (3) the core (Fig. 1). The combination of the top layer of the mantle and the crust is called the lithosphere. The lithosphere (also known as plates or lithospheric plates) effectively floats on top of another layer of the mantle –– the asthenosphere. The movement of the plates results from a combination of (1) rigid lithospheric plates on top of a ductile asthenosphere and (2) the heat produced by radioactive decay in the mantle. This plate movement is basis of plate tectonics. The processes relating to plate tectonics are why we have many landforms on earth, including volcanoes, large mountain ranges, and some island chains.
Another basic component of plate tectonics is the difference in density between the two types of crust: oceanic crust and continental crust. Oceanic crust is rich in the heavy elements of iron and magnesium. Continental crust has higher concentrations of the lighter elements of silica and aluminum. The differences in composition result in oceanic crust being denser than continental crust. Both crusts are less dense than the mantle, so they “float” on top of the mantle.
Oceanic crust also is much thinner (5-10 km thick) than continental crust XXXXXXXXXXkm thick). As the name suggests, oceanic crust comprises the bottom of the oceans; continental crust comprises the continents, including land above and below sea level. Table 1 shows details on the differences between oceanic crust and continental crust.
Table 1. Characteristics of continental crust and oceanic crust.
Plate boundaries are where most earthquakes and volcanoes occur. When plates collide or move past each other, they encounter resistance from the other plate. As the plates continue to exert more and more force on each other, the stress
increases until they ultimately slip, or rupture; then they move into a position of less stress. When they rupture, they release energy in what we know and feel as an earthquake.
The location of the earthquake rupture is called the focus, and earthquakes are generally refe
ed to as a shallow (0-70 km), intermediate XXXXXXXXXXkm), or deep XXXXXXXXXXkm) depending on the depth of the focus. Different types of plate boundaries will have different depths of earthquakes.
Part II. Types of Plate Boundaries
The type of landforms that are created by tectonic processes depend on what interactions occur between the different crust types. There are three interactions that can occur, based on the relative movement of the plates (see Figure 2 and Figure 3):
· Divergence – plates moving away from each othe
· Convergence – plates moving towards each othe
· Transform – plates moving past each othe
Figure 2. Map (top) showing the locations of plate boundaries and the location of the tectonic plates on Earth. Use this figure when answering questions for Part 1 of lab. Cross sections (bottom) of the three types of boundaries: (a) divergent, (b) convergent, and (c) transform.
Divergent Plate Boundaries
Divergent plate boundaries (Fig. 2a) form when two plates move away from each other. Plates move apart when material rises from the asthenosphere toward the surface of the plates. This rising material forces the plates apart, melts into hot magma, and eventually cools to create new oceanic crust. Due to the magma rising to the surface, there are shallow earthquakes at diverging plate boundaries.
Divergent plate boundaries typically are found at mid-ocean ridges, located at the bottom of the ocean floor and thus are composed of oceanic crust. When divergence occurs in oceanic crust, it is commonly called seafloor spreading.
Divergent plate boundaries also can occur in continental crust, resulting in a continental rift. If the continental rift continues to widen, it ultimately become a rift lake of a new ocean basin.
Convergent Plate Boundaries
Convergent plate boundaries (Fig. 2b) form when two plates move towards each other, resulting in either subduction or collision. Subduction occurs when one plate moves underneath the other plate. Collision occurs when two plates collide with each other accordion-style. The type of convergence that results when two plates meet is determined by whether the plates are comprised of oceanic crust, continental crust, or both. When two continental plates converge, a collision zone will form. When either two oceanic plates converge or an oceanic plate converges with a continental plate, then a subduction zone will form.
For subduction zones, the more dense plate will subduct under the less dense plate. For oceanic-continental subduction zones, the oceanic plate always will subduct under the continental plate because oceanic crust is more dense than continental crust. For oceanic-oceanic subduction zones, the more dense oceanic plate will subduct under the less dense oceanic plate.
At convergent-subduction plate boundaries, volcanoes can form when those parts of the plate being subducted melt below the other plate. The molten material then rises upward through the crust to form a volcano. In addition, this type of plate boundary is associate with shallow, intermediate, and deep earthquakes because the plate being subducted is forced deep within the mantle. When a plate is subducted, it encounters a huge amount of resistance as it moves under the other plate.
Transform Plate Boundaries
Transform plate boundaries (Fig. 2c) form when two plates move laterally past each other; these plates do not diverge or converge. Most transform boundaries result from each plate is moving away from two different, but nea
y, divergent plate boundaries. Transform plate movements can create shallow earthquakes but do not form volcanoes.
Figure 3. Another map showing the locations of plate boundaries including the formation of volcanoes and earthquake zones due to convergent, divergent and transform boundaries.
Part III. The San Andreas Fault
A famous example of both a transform and a strike-slip fault is the San Andreas fault system (Figure 4). A transform fault occurs along transform plate boundaries; most are found in the ocean basins along mid-ocean ridges, but some are ove
idden by continental crust that becomes faulted. The crust on either side of a transform fault moves parallel to the fault itself. Thus, transform faults are a type of strike-slip fault. However, since some strike-slip faults occur at locations away from plate boundaries, not all strike-slip faults are transform.
Along the western margin of North America, plate boundaries take several forms. The San Andreas transform fault is the product of a continental plate (the North American plate) ove
iding an oceanic transform plate boundary. At its northern end, the San Andreas fault meets a seafloor spreading center and a subduction zone at the Mendocino Triple Junction (a triple junction is where three plates intersect). Strike-slip faults often create linear valleys, or rifts, along the fracture zone, such as those along the San Andreas (Figure 4).
Figure 4. Plate boundaries of western North America, including the San Andreas fault.
Part IV. Human-Induced Earthquakes
The overall risk to natural or human-induced seismicity is shown in Figure 5. Recently, human activities have altered the natural processes occu
ing along