Unit
Plate Tectonics
Title
2. Plate Patterns
Summary
Starting with an earthquake epicenter map (generated by students in The Big One activity), students add information about where active volcanoes are located and the location of the mid-ocean ridges. With the combined information about volcanoes, mid-ocean ridges, and earthquake epicenters, student can trace the boundaries of the Earth’s major plates. On individual student maps containing earthquake epicenter data, they outline the plate boundaries, learn the names of each plate, and use colored pencils to highlight volcano zones and mid-ocean ridges. Future activities in this box have students adding plate direction and speed information to student maps as well as labeling 4 different types of plate boundaries: continent-continent convergent boundaries, subducting convergent boundaries, transform boundaries, and divergent boundaries. The direction and speed of many plates can be inferred from the opposition of mid-ocean ridges on one side of the plate and volcano zones on the other.
Objectives
Can recognize that the Earth’s crust is broken into large, independently moving pieces known as tectonic plates.
Can define the boundaries of the tectonic plates using data about the location of earthquake epicenters, active volcanoes, and mid-ocean ridges.
Can use latitude and longitude information to plot locations on a world map.
Vocabulary
Earthquake
Epicenter
Volcano
Mid-ocean ridge
Tectonic plate
Plate boundary
Time
20-30 min add volcano data to map
20-30 min learn about mid-ocean ridges and add them to the map
45-50 min trace and color code plate boundaries and label with the names of tectonic plates
Grouping
Individual
Materials
· Copies of the USGS/NPS World Earthquake Map for each student (download a copy of the “World Earthquake Map” from the USGS/NPS website http://www2.nature.nps.gov/Geology/usgsnps/misc/pdfdocs.html under PDF documents)
· Overhead transparency version of the World Earthquake Map
· 1 teacher copy of the USGS/NPS World Plates Map for reference (download a copy of the “Earth’s Tectonic Plates” from the USGS/NPS website http://www2.nature.nps.gov/Geology/usgsnps/misc/pdfdocs.html under PDF documents)
· 1 teacher copy of the Mid-Ocean Ridges Map for reference (print a copy from the USGS website http://pubs.usgs.gov/gip/dynamic/baseball.html).
· Overhead projector
· 4 colors of overhead projector pens
· 1 copy of the Volcano List for the class, cut into strips with one line per strip.
· Large world map used in The Big One activity (An alternative strategy is to use a copy of the “This Dynamic Planet” poster from the USGS, $14 + $5 handling http://www.minerals.si.edu/tdpmap/order.htm).
· Colored pencils or markers
· Red 1/4” to 1/2” removable color dots (available in most stationary stores and drug stores for labeling maps and documents, each package usually contains 4 colors of dots: red, yellow, green and blue – only red is needed for this activity)
· Masking tape or the somewhat less sticky blue or green painters’ tape
· Optional: photos or a brief video clip of the mid-ocean ridges (see Sources section for good sources of images and videos)
Setting
Classroom
Teacher Background
As early as the 1920’s scientists recognized that earthquakes lined up along fault zones and were not randomly scattered across the globe. The technology improved dramatically in the 1960’s when standardized seismic monitoring stations were established around the globe to police the ban on above-ground nuclear testing. The location of active volcanoes also lines up along these same zones. For example, the Pacific Ocean is surrounded by volcanoes and earthquake zones – commonly known as the “Ring of Fire”. These zones mark the boundaries of the Pacific Plate. Other tectonic plate boundaries may also be identified in this way.
Yet to see all the borders you also need to look under the ocean. In the late 1950’s, the exploration of the oceans revealed enormous mid-ocean ridges that zig-zag across the ocean floor between continents, nearly encircling the globe in places. These mid-ocean ridges rise on average 4,500 kilometers above the ocean floor and reach peaks higher than most mountains on land. More recent explorations have revealed that the mid-ocean ridges are characterized by huge upwellings of magma similar to volcanoes on land. Incredibly, life, in the form of archaebacteria and other species, exists along the mid-ocean ridges, surviving on the chemicals and nutrients exiting from hydrothermal vents.
Combining information from all these sources (earthquakes, volcanoes and mid-ocean ridges, it is possible to draw the boundaries of all the Earth’s major plates. The seven largest plates are easily identified: African Plate, Antarctic Plate, Eurasian Plate, Indo-Australian Plate, North American Plate, Pacific Plate, South American Plate. The smaller Philippine and Caribbean plates can be outlined using the prominent volcano and earthquake data. The Cocos and Nazca plates can be distinguished using mid-ocean ridge data.
Only the Juan de Fuca, Scotia, and Arabian plates are easily overlooked. In fact, I generally don’t emphasize these 3 plates if my students don’t identify them themselves since it is not essential to me that they memorize all the world’s tectonic plates, only that they recognize how the crust is broken into moving plates and that they understand how the plate boundaries can be determined with earthquake, volcano and mid-ocean ridge information.
Several critical questions remain:
· Why are there earthquakes, volcanoes and ridges at the plate boundaries?
· How come you don’t see earthquakes at the midocean ridges so much?
· Why are there earthquakes but not volcanoes in the Himalayas above India?
All these questions are related to the differences in what is happening at each of the plate boundaries. (I choose to hold off on discussing these issues with my students until after they learn about the interior of the Earth, convection cells, and sea floor spreading.)
Plate boundaries may be divided into 3 main categories: convergent boundaries where plates collide, divergent boundaries where plate pull apart, and transform boundaries where plates grind past each other. Convergent boundaries in turn have different characteristics depending on if it is 2 pieces of continental crust colliding (continent-continent convergent boundary) or if 1 piece of oceanic crust is diving down below a piece of oceanic or continental crust (subducting convergent boundary).
· With divergent boundaries, like the mid-ocean ridges, Iceland, and the African rift valley, you get few earthquakes because the plates are pulling apart, not storing up energy as they collide or rub past each other. Instead, a gap forms between the plates and magma is pushed up from the mantle below to fill in the hole. Thus, you get lots of volcanoes, thermal vents, and great broken rifts in the earth.
· With transform boundaries, like the San Andreas fault (most of other transform boundaries lie on the ocean floor), you get lots of earthquakes and only occasional volcanic activity. The plates are moving past one another and storing energy between them until the friction holding them together gives way in the form of an earthquake.
· With subducting convergent boundaries, as in the northwestern edges of the Pacific Plate, the west coast of South America, and the northeastern edges of the Indo-Australian Plate, you get a combination of volcanoes and earthquakes. The lighter plate floats on top while another plate dives below the edge in a process known as subduction. As this occurs, the submerging plate melts and bubbles up through cracks in the overlying crust as volcanoes.
· With a continent-continent convergent boundary, like the Himalayas at the boundary between the Indo-Australian and Eurasian plates, you get lots of earthquakes but very little volcanic activity. That is because both continental crusts are light and resist subduction. Instead, they buckle and crumple against one another, gradually rising skywards inch by inch. In fact, the Himalayas continue to rise at the rate of approximately 5 mm a year.
For ways to model these different plate boundaries with students, see the Sea Floor Spreading activity.
Student Prerequisites
Students should have participated in labeling and discussing the large classroom map with earthquake epicenter data. Students should already know that earthquakes cluster in lines along faults and that these faults occur at the edges of pieces of land that are colliding or grinding past one another.
Getting Ready
1. Make copies of the “World Earthquake Map” from the USGS/NPS website http://www2.nature.nps.gov/Geology/usgsnps/misc/pdfdocs.html
2. Make one copy of the Volcano List for each class, cutting them into strips with information about one volcano on each strip.
3. Make a transparency version of the World Earthquake Map.
4. Display the large map with earthquake data already plotted at the front of the classroom.
5. Set out color dots and colored pencils.
6. Print out reference sheets - Earth’s Tectonic Plates (http://www2.nature.nps.gov/Geology/usgsnps/misc/pdfdocs.html) and Mid-Ocean Ridges Map (http://pubs.usgs.gov/gip/dynamic/baseball.html).
Lesson Plan
Volcano data
1. Briefly review the patterns discovered by the students from the previous activity (The Big One).
2. Pass out the volcano data strips and a single red color dot per student. Describe to them that their job is to read about their volcano and use the latitude and longitude information to plot the volcano on the map.
3. One by one, have students come up to the front of the room to read the information about their volcano then plot their volcano on the map. While they plot their information, another student can come up and describe their volcano. Regulate the flow so that no more than 2-3 students are plotting their data on the map at one time.
4. When all students have gone and all the data is plotted on the map, discuss any patterns you see on the map as a class. The goal here is have students recognize that volcanoes and earthquakes often line up along the same zones. Point out the ring of earthquakes and volcanoes that encircle the Pacific Ocean. This prominent zone is known as the “Ring of Fire”.
Mid-ocean ridges
1. Describe to students that there are many volcanoes under the ocean. Briefly discuss the discovery and characteristics of the mid-ocean ridges. If available, show the students photos or a video clip of the bizarre life forms near the ridges and thermal vents.
2. Refer to the Mid-Ocean Ridges Map and place masking tape on the class map where the mid-ocean ridges are located. Point out how the mid-ocean ridges nearly encircle the globe in places (such as going almost all the way around Antarctica) and how they cross land masses in 2 places – Iceland and East Africa.
Trace and color code plate boundaries
1. Give each student a World Earthquake Map.
2. Distribute the colored pencils so each student has at least 3 different colors available.
3. Place your overhead copy on the projector.
4. Select one color to represent the mid-ocean ridges. Set up a legend in one corner of the map and create a key showing that that color represents mid-ocean ridges. Refer to the large class map and trace the mid-ocean ridges in that color.
5. Select another color to represent volcanic zones. Add that color to your key. Refer to the large class map and trace the volcanic zones. Some volcanoes (Kilauea in Hawaii, Mount St Helens in Washington, Vesuvius, Etna and Stromboli in Italy, and Erta Ale in Africa) don’t appear to have others nearby. Use a single dot of color to represent them is so desired.
6. Select another color to outline the plate boundaries. Connect the dots and lines to trace the boundaries of the major tectonic plates. If students overlook the Juan de Fuca, Scotia, and Arabian plates, that’s OK. Also, the boundary between the North American and Eurasian plates is difficult to identify. If students insist on placing it through Alaska based on the earthquake evidence rather than through Russia as it truly lies, don’t be surprised and use your judgment as to whether to let them proceed with that error or not.
7. Finally, label each of the plates with the name of each plate. If you wish, label the “Ring of Fire” as well.
8. Turn these maps in or store them in a safe place for use in future lessons (such as the Sea Floor Spreading activity).
Assessment
- Collect students’ color coded maps.
- Assign a plate puzzle as homework where students cut out, assemble, and label the Earth’s tectonic plates. My favorite tectonic plates puzzle is produced by the USGS/NPS. (download a copy of the “Plates Puzzle 1 and 2” from the USGS/NPS website http://www2.nature.nps.gov/Geology/usgsnps/misc/pdfdocs.html under PDF documents).
Going Further
- Investigate and build models of different types of plate boundaries. See the Sea Floor Spreading activity and the Evidence for Plate Tectonics activity.
- Read excerpts from the booklet “This Dynamic Earth” which explains the theory of plate tectonics in greater detail. See the Sources section for how to get a copy.
- Travel (virtually) to the plate boundaries around the world and explore the geology of different countries that straddle 2 plates. See the Plate Boundaries Around the World activity.
- Research the recent discoveries of deep ocean life near the mid-ocean ridges.
- Use Google Earth to visit volcanoes and earthquake regions around the world! Download Google Earth (http://earth.google.com/download-earth.html) then install volcano layers from the Smithsonian (http://www.volcano.si.edu/world/globallists.cfm?listpage=googleearth) and visit the 1906 Earthquake in San Francisco courtesy of USGS (http://earthquake.usgs.gov/regional/nca/virtualtour/).
Sources
Three excellent resources for more information on plate theory include:
· The booklet, “This Dynamic Earth”, published by the USGS, is indispensable, providing all the background information a teacher could want and more. It can be downloaded in its entirety from the USGS website (http://pubs.usgs.gov/gip/dynamic/dynamic.html).
· The poster and downloadable/printable handouts, “This Dynamic Planet”, provides maps and figures showing plate boundaries, volcanos, earthquake data, impact craters and more (http://www.minerals.si.edu/tdpmap/index.htm). The back of the map has excellent information on different types of boundaries, rock ages, hot spots and more. You can even download the data that was used to generate the map for further analysis.
· The website “What on Earth is Plate Tectonics?” by the USGS and the National Parks Service (http://www2.nature.nps.gov/Geology/usgsnps/pltec/pltec1.html). In very easy to understand language, the site walks the user through the composition of the Earth, plate tectonics theory, and Earth history in view of plate tectonics.