Plate Tectonic - Plate Tectonics (1) Lab
 OBJECTIVES: Demonstrating features caused by stress. Explaining that stress in the Earth causes earthquakes. VOCABULARY: converging diverging mountain slip/slide valley MATERIALS: 5 lb. bag of flour sealable plastic bags water plastic spoons measuring cups containers for mixing Students demonstrate the stresses that occur at plate boundaries. A convergent plate boundary
 BACKGROUND: As they move, plates interact at their edges or boundaries. As described in the Pre Lab, in some places two plates move apart from each other; this is a diverging plate boundary. In other areas, two plates move together; this is a converging plate boundary. Finally plates can also slide past each other horizontally. This is called a transform plate boundary. Plate movement generates stress in the rocks at plate boundaries. The type of stress is different at each type of plate boundary. At converging plate boundaries rocks are squeezed (compression), at diverging plate boundaries they are stretched (tension or extension), and at transform boundaries they are pushed past each other (shear). Because the plates are rigid rock, they resist this motion until they break, creating earthquakes. The compression at converging plate boundaries also creates mountains; all of the worlds large mountain ranges formed at this type of boundary. This exercise allows the students to experience how stress on the outer portion on the Earth effects the plates. They will deform, or stress, "plastic" earth with converging, diverging, and transforming motions. PROCEDURE: Explain to the class that plate motion causes stress at plate boundaries. Remind students of the three ways plates interact: converging, diverging, and transform motion. You may wish to demonstrate these motions with your hands.    Tell the students that they will be making mountains and valleys in the same way that plate movements form these features. Be sure to compare mountains and valleys with the students. Explain that mountains form at converging plate boundaries, where plates squeeze together, and valleys are more common where plates move apart, at diverging plate boundaries. Transform plate boundaries often form a combination of small mountains and valleys.    Have the students make a flour and water mixture. Have them mix 2 parts of flour with 1 part of water in small containers (Cool Whip or margarine containers work well). They should blend the mix with a spoon until it becomes pasty. Check the mixture before the students put it into the plastic bags, making sure that is neither too wet nor too dry. Have the students pour their mixtures into the plastic bags. Make sure each baggy is "zipped" tightly or you will end up with a mess on your hands. If the bags are sealed correctly the mixture will remain pliable for up to 5 months. You may wish to have the students take the plastic bags home to demonstrate what they did to their parents.    Demonstrate converging, diverging, and transform plate boundary motions to the students. Have the students stress the bags as shown in the diagrams below. Tell the students to observe what happens as they apply each type of stress. Go around to each of the students, making sure they can point out mountains and valleys. When the students try to "diverge", they should not apply a lot of pressure because the paste will not gush up. In a real diverging zone, however, lava fills in the void. In conclusion, discuss that when the outer portion of the Earth is under stress, earthquakes take place to relieve the stress.