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LESSON FOUR - Building Mountains ANSWER KEY Lesson Four: Building Mountains Vocabulary Station Part A: Describe what is meant by each of the following terms. You may write in jot note form. Deformation Compression - breaking, tilting and folding of rocks - “de” means undo - “form” means shape - type of stress on rocks that squeezes rocks together - makes rocks denser and smaller in volume Tension Shearing - type of stress that pulls on rocks causing them to stretch over a larger area; rock becomes thinner in the middle - type of stress on rocks that pushes rocks in 2 opposite directions causing rocks to twist or bend apart - may also see rocks slide past each other Fold Rift Valley - any bend in a rock; either upward or downward - valley created when block of land between two normal faults slides down Plateau Syncline - raised area created when block of land between two faults is thrust upward - a downward fold in a rock Anticline - an upward fold in a rock Lesson Four: Building Mountains Discussion Question Station Answer the following questions in sentence form. 1. Temperature is one of the four factors determining whether or not a rock is likely to fault (break) or fold. Increased temperature usually results in rocks folding. Lower temperatures usually result in a fault or break in the rocks. The other two factors listed below also determine whether or not rocks will fault (break) or fold. Tell the effects of the various factors on rocks. TYPE OF ROCK - brittle versus ductile Brittle rock is more likely to fault (break); ductile will fold (bend) HOW STRESS IS APPLIED - quick application of pressure versus slowly applied pressure Pressure applied quickly will cause a rock to fault; applied slowly, a rock will fold. 2. List four ways that mountains can be created. Folding, faulting, dome building, volcanic activity, colliding continents 3. What is the difference between an underwater trench and an underwater ridge? Underwater trench is a deep underwater valley that is formed when oceanic and continental crust collide at a subduction zone. These are located at converging boundaries. An underwater ridge is found in the centre of underwater mountain chain (also known as a ridge). This ridge is created at a divergent boundary. 4. Draw the following types of mountain formations: Folded Mountains Dome Mountains Fault Block Mountains Reverse Fault Mountains Lesson Four: Building Mountains Hands-On Station The purpose of this activity station is to show how mountains can form by folding. Materials: 5 rectangular strips of modelling clay, each a different color and the same size Procedure: 1. Place one piece of clay on your desk. Lay the other pieces one by one on top of each other to form a pile. 2. Place your hands at either end of the clay with the palms facing inward. 3. Slowly, move your hands together, applying pressure to each side of the clay. 4. Stop when your hands are about 10 centimeters apart. 5. Draw a diagram of your clay below. Questions: 1. What do your hands represent in this activity? Pressure (tension) 2. What does the modelling clay represent in this model? Rock (ductile) 3. What happens to the clay as you move your hands together? Begins to fold upward and downward 4. Why doesn’t the clay break as it is squeezed together? It is ductile or bendable because it is soft. 5. Write a summary statement that answers the question: “How do mountains fold?” Include a diagram with your answer. Answers will vary. Students should include information about pressure being applied slowly will more likely cause a rock to bend. Whether or not the rock is ductile will also have an effect on folding. Lesson Four: Building Mountains Computer Station CLICK ON Continental Slide http://cgi.pbs.org/wgbh/aso/tryit/tectonics/convergent.html 1. If the Earth’s crust separates at divergent boundaries and creates new crust, why doesn’t the Earth “grow” in size? The answer is subduction. In locations around the world, ocean crust subducts, or slides under continental crusts and turns back into molten rock. 2. At approximately what depth (in kilometers) does the rock of the oceanic plate begin to turn to molten rock? At a depth between 300 and 700 kilometers, the rock of the descending plate melts. CLICK ON Continental Crush http://cgi.pbs.org/wgbh/aso/tryit/tectonics/crush.html 1. Why does the oceanic crust slide beneath the continental crust at a subduction zone? This is because the land mass is more buoyant, or lighter, than the ocean floor. 2. What happens when two land masses meet? The two crush together at what is known as a collisional boundary. They crumple and fold. Some pieces of land are thrust over or under other pieces. The result is a mountain range. 3. The Himalayas and the Appalachian Mountains were both formed by colliding continental plates. How do scientists know that the Appalachians were formed before the Himalayas? All that remains of the Appalachians are eroded tops. The Himalayas are still high and jagged, comparatively not as affected by erosion. CLICK ON Sea-Floor Spread http://cgi.pbs.org/wgbh/aso/tryit/tectonics/divergent.html 1. New ocean floor is created at what part of an underwater mountain chain? It is called a ridge. 2. Sea floor spreading is the name scientists give to the formation of new crust on the ocean floor. CLICK ON Slippin’ and Slidin’ http://cgi.pbs.org/wgbh/aso/tryit/tectonics/transform.html 1. Describe how an earthquake occurs at a transform boundary. Two plates move against each other, building up tension, releasing the tension in a sudden and often violent jerk. This sudden jerk creates an earthquake.