“Plate Tectonics, Earthquakes and Volcanoes”

Eileen Van der Flier-Keller, March 2011

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Workshop Manual Contents Plate Tectonics Earthquakes and Volcanoes Schedule: Demo 1 Demo 2 Activity 1: Activity 2: Activity 3: Activity 4: Activity 5:

Earth as an egg Coincidence of volcanoes, earthquakes and plate boundaries Plate Tectonics in our Own Backyard Cross section using Juan de Fuca Plate relief map Volcanoes and viscosity Fabulous folds Earthquakes and seismic waves

Resources: Pacific Northwest Plates overheads Geoscape Victoria Dancing Elephants Floating Continents book Workshop manual and EDU sheets

Useful websites: www.earthlearningidea.com www.edgeo.org www.earthsciencescanada.com

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Demo 1: Earth as an Egg Background The Earth is actually a ball of rock that weighs 6.6 sextillion (6.6 x 1021) tons. When the Earth formed, the outer layer cooled more rapidly and a crust formed. Gravity caused the heavier elements to settle toward the middle where they remain. There are three main zones within our planet: • Crust - consists of solid rock and a very thin layer (centimetres to metres) of soil. The crust is approximately 8 km thick under the ocean and 32 km thick where there are continents • Mantle - this zone is 2896 km thick and consists of semi-solid rock. The temperature is around 871°C at the outer part where it meets the crust, but it gets progressively hotter downward. Parts of the mantle are in motion as a result of convection currents • Core - this can be divided into an outer core and an inner core. The outer core is 2252 km thick and consists of melted iron and nickel at a temperature of 2200°C. The inner core is 1287 km to the centre of the Earth. It is a mixture of solid iron/nickel at a temperature of 5000 to 7000°C Materials • Hard-boiled egg • Knife • Overhead of cut-away Earth Notes Different parts of the Earth’s internal layers behave differently. The mantle has a strong, hard, upper layer that together with the crust is called the lithosphere. The lithosphere is between 50 and 100 km thick and behaves as a strong, cool, rigid unit. The lithosphere is broken into 10 to 12 major plates, which contain the world’s continents and oceans. These plates move around at the surface of the Earth. Continents are like rafts embedded in the lithosphere. In the mantle under the lithosphere is a partially molten layer called the asthenosphere. The asthenosphere is much weaker and hotter than the lithosphere because it is partially melted. The asthenosphere has the consistency of toothpaste and is able to move slowly under pressure. The lithosphere and our ‘plates’ are able to move around because of the weak and partly melted asthenosphere below them.

See another idea to model the Earth: “Whole World in Your Hands” in South Vancouver Island Earth Science Fun Guide.

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Demo 2: Coincidence of plate boundaries, volcanoes and earthquakes Background: Unlike in the eggshell model of the earth (where the plates aren’t moving), plates move around and meet each other at boundaries. Distribution of volcanoes and earthquakes around the world is not random. Earthquakes and volcanoes are usually located together in certain areas which correspond to the boundaries between plates. The occurrence and locations as well as the types of volcanoes and earthquakes are directly related to plate tectonics.

Materials: • World map • Overhead of plates and overhead map of earthquakes and volanoes • List of volcanoes • Pencil crayons Procedure: 1. On a blank map, using a symbol such as a triangle, plot the locations of the volcanoes on the list. You could use different colour pencils for different types of volcanoes (e.g. shield volcanoes, stratovolcanoes (composite), fissure eruptions etc). Then plot the earthquake locations. An extension activity would be to have the students research the focal depths of some of the earthquakes and plot these in different colours (shallow focus earthquakes occur from the surface to depths of 70km, intermediate focus earthquakes occur from 70 to 300km below the Earth’s surface, and deep-focus earthquakes occur between 300 and 700km). 2. What do you notice about the distribution of volcanoes and earthquakes? 3. Overlap a plate boundary map onto the earthquake and volcano map. What do you notice?

Notes:

Characteristics of the three types of plate boundaries are: Diverging: Here the lithosphere is being stretched and pulled apart, so the sides (plates) move apart and magma from below wells up into the gaps. As a result of the stretching and rising magma you get  Shallow-focus earthquakes  Major topography -i.e. long high ridges, with deep rift valleys or fissures in the crust in the middle  Volcanic eruptions along these narrow deep rifts Converging: Here plates are colliding and one plate is forced under (subducted below) the edge of the other (overriding plate). Tremendous stresses that the rocks on both plates are subjected to during convergence and subduction lead to  Shallow-focus to deep-focus earthquakes  Volcanic activity on the overriding plate (as the crust below melts) e.g. stratovolcanoes  Mountain belts on the overriding plate as the pressure of the plates colliding forces the crust upwards. Transform: Plates are moving side by side in opposite directions. Friction causes  Shallow-focus earthquakes  Features are moved sideways and are offset 3

Activity 1: Plate Tectonics in Our Own Backyard EDU Model Explore 1. What parts of the Earth (layers) are involved in plate tectonics? How thick do you think plates are? 2. What are the plates here around BC? 3. Are they all moving? Which directions are the plates moving in? 4. What are the possibilities for how plates might move relative to each other? 5. What happens at the edges of plates? Do the Activity: Reconstruct using the materials (foamies, arrows, labels), the plate scenario here in the Pacific NW. Where is Vancouver Island in this model? Discuss • • • • • • • •

Why does the Juan de Fuca plate ‘subduct’ below the North American Plate? What are some of the consequences of subduction? What might cause the plates to move? Where on your model will there be volcanic activity? Where will there be earthquakes? Where is the oldest ocean crust? What happens to the sediments and the rocks on the leading edge of the North American plate when the islands collide with the North American plate? What happens every time a terrane is added?

Understand Try to recreate with the model materials the plate setting in the Atlantic Ocean (with North America and Europe). What do you think the plate model would look like for the Pacific Northwest in several millions of years? Use the model materials to demonstrate the plate actions in the Queen Charlotte region (or the San Andreas region).

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Activity 1: Plate Tectonics in Our Own Backyard Instructions Materials:

2 blue thinsulite camping foamies (Juan de Fuca and Pacific Plates) 1 piece of mattress foam (representing the North America plate) masking tape labels for Pacific plate, North America plate, Juan de Fuca Plate, Cascadia Subduction zone, Juan de Fuca Ridge, and 3 cut out arrows random objects such as paper cones, styrofoam shapes (to simulate volcanic islands, bits of continents)

Review the 3 types of plate margins and demonstrate the convergence of the thin ocean crust and the thicker continental crust by bringing the foamies and the mattress foam together. Use the materials (and http://geoscape.nrcan.gc.ca/vancouver/earth_e.php , http://mineralsciences.si.edu/tdpmap/) to construct a model of the three plates that interact in the western part of North America and offshore. Add labels and arrows to indicate plate movement and identify the ridge and subduction zones. Two chairs can help to hold the diverging plates together. Simulate the addition of terranes by adding volcanic islands (Styrofoam) to the Juan de Fuca plate. Repeat the plate motion. Use a map of the Pacific Ocean floor to identify potential future terranes that may add to North America if it continues to move W towards and over the Pacific Ocean crust? Background: The story of the Rocky Mountains is only one part of the history of how the western edge of North America was built. 180 million years ago, the edge of the continent was close to the current location of the Alberta/British Columbia border. A shallow tropical continental shelf formed along the margin of the continent. All of the land west of this location has been added to the original continental edge due to the forces of plate tectonics. The converging plates built up the Cordillera. North America started to move westward as part of the breakup of the supercontinent Pangaea, ploughing towards and over the Pacific Ocean floor. With this movement, the ocean crust was overridden by and subducted beneath, the continental edge. Coincident with this movement, volcanic islands (offshore island arcs and ocean plateaus), ocean basin sediments, displaced continental fragments, and even parts of the ocean floor itself were scraped off and plastered onto the old continental edge. These terranes which make up most of British Columbia and the Cordillera, are all ‘exotic’ rock units, in that they are internally consistent but then change abruptly across large faults. Did you Know? An amount of ocean floor equal in length to one third of the Earth’s circumference has been subducted below North America in the last 150 million years.

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Activity 2: Cross-Section Using Juan de Fuca Plate relief map Background: The three main plates which affect us on southern Vancouver Island are the North American plate (we’re on it), Juan de Fuca plate (it’s out to sea), and the Pacific plate (on the other side of the Juan de Fuca plate towards the west). Materials • Juan de Fuca Plate Relief Map • Graph paper, rulers, pencils Procedure 1. Using the detailed portion of the Juan de Fuca Plate Relief Map, construct a topographic crosssection from one side of the map to the other going roughly east-west across the Juan de Fuca or Gorda Ridge. Place the graph paper along the line of the cross-section and mark off each contour (and record its height or depth) on the top edge of the paper. Draw a horizontal line below and a vertical scale at each end. The scale will extend above and below the cross section line. Transfer the contour heights to points on the cross section and the join the points. 2. Label the features through which you have drawn the cross section. 3. a) Draw in the plates (Juan de Fuca, North American and Pacific) below the surface topographic line. b) Show the subducting Juan de Fuca plate and where you think rising magma occurs. c) Label the plate boundaries. d) Use arrows to show the directions of plate movement. e) Mark in where you would expect to have earthquakes occurring. Find out where the latest earthquakes have been in the region (www.pgc.nrcan.gc.ca) and locate them on the map. How does this fit in with what you have just drawn?

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Activity 3: Thar’ She Blows Volcanoes and Viscosity Instructions and EDU Model Materials:

transparent plastic cups (2 for each group doing the experiment) Dark coloured soft drink (coal, root beer) to nearly fill one cup of each group Clear corn syrup (to ¾ fill the other cup) Drinking straws (one for each cup), Newspapers (to keep the work space somewhat clean)

Explore: How do you think the eruptions of the coke and corn syrup will be different? How are the two liquids unlike real magma? • • •

Fill the cups, one with root beer, the other with corn syrup, and place on the newspapers Using a straw, lightly blow into the root beer until you start to produce bubbles Now with the same amount of ‘blow’, blow into the corn syrup. (nothing will happen). Blow harder until you get the corn syrup to ‘erupt’.

Discuss: Based on observations, respond to the following questions. • How were the eruptions of root beer and corn syrup different? • What is the physical property that makes the ‘magmas’ different from each other? • How would this relate to the types of volcanoes each might form? • Which type of magma would erupt between the Juan de Fuca and Pacific Plates? Why? • What kind of magma erupted to form Mount St Helens? What about the volcanoes in BC? • How do different types of magmas form?

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Activity 4: Fabulous folds Instructions and EDU Model Materials Required: Transparent plastic box Strong cardboard cut to tightly fit box as a vertical partition (it should be taller than the box so that it can be held and pushed sideways) Dry sand White flour Explore: The layers of sand and flour represent layers of sediments like sand and mud. Where would we see sand and mud being deposited forming right now? Stand the cardboard vertically at one end of the plastic box and pour a layer of sand into the plastic box until it is about 1cm deep. Sprinkle a thin layer of flour on top of the sand. Alternate layers of sand and flour until the box is about half full. Slowly move the cardboard towards the opposite end of the box, simulating the force of the terranes pushing against the flat lying sedimentary layers at the edge of ancient North America Discuss: How did the layers change? Plates are mostly made of rock. Do you think rock will fold or would you expect it to break? What structures can you identify? Understand: Cool Facts: If you piled up all the sedimentary rocks that were once laid down flat at the ancient edge of North America, you would have a thickness of approximately 15km (that is around 15 times the depth of the Grand Canyon). If you undid all of the horizontal shortening (i.e. pulled all of the thrust fault slices back so they were in their original positions), rocks now exposed at Field near the British Columbia/Alberta border would have been located close to Vernon, over 200 km to the west.

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Activity 5: Earthquakes and Seismic Waves Materials:

Slinky

Explore and Discuss: Ask the Q “What happens to the earth during an earthquake?” Model an earthquake using a stick that you break. What kind energy is released as the stick breaks? In an earthquake how is the energy released? Discuss how seismic waves move through the earth during an earthquake. These waves can cause mass destruction, even at great distances from the epicentre. • • • •

Have students simulate the two main types of waves generated. Students can work in pairs Sitting opposite one another, have each team member hold one end of the slinky. P-waves (compression or primary) arrive first. These waves travel quickly by pushing and pulling their way along. The students can gain a better sense of how these waves move by alternately pushing and pulling the ends of the slinky in a straight line The second waves are S-waves (shear or secondary). These waves travel more slowly from side to side in an undulating fashion. Students create this by moving the ends in opposite directions to either side. They will discover that there is a certain point where you get a uniform, S-pattern running along the length of the slinky

Understand: Those who have experienced an earthquake relate that they can feel the distinct movements. Do you see why?

Human Wave Demonstration Have the students get into two lines, all facing forward and putting their hands on the person in front’s shoulders. Have someone ‘be’ the earthquake and when they say “earthquake” they will touch the back person in each line with their hand. Each line should then allow a p and then an s wave to propagate down the line.

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Background Information Most of the solid earth is beyond our direct observation. Earth scientists have devised ingenious methods to provide answers to questions concerning the structure of the interior and crust of the earth. Much of our current knowledge of plate tectonics and margin processes has come from the analysis of earthquake records.

Interpreting Seismic Records Earthquakes are vibrations of earth that occur when rigid lithosphere breaks, and “springs back” to its original shape, rapidly releasing stored energy. This energy radiates in all directions from the source of the earthquake (called the focus) in the form of seismic waves. Seismograph instruments located throughout the world amplify and record the ground motions produced by passing seismic waves. Seismograms (Fig. 1.2) are then used to determine the time and location of an earthquake. Note the difference in amplitude between the P, S and L waves on the diagram.

Figure 1.2. Seismogram showing the arrival times of P, S, and surface waves.

A website with an excellent explanation and graphics of the way that earthquakes are studied and described: http://www.seismo.unr.edu/htdocs/abouteq.html.

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