Texas Science Grade 8 Investigations

CHAPTER 9 • Plate Tectonics MATERIALS LIST Investigation 9.3 Earth’s Two Major Mountain Ranges What causes Earth’s major mountain ranges to form? The Andes and the Himalayas are the two highest mountain ranges on Earth. These two majestic mountain ranges contain mountains over 22,000 feet in elevation. Both were formed by the same process; converging tectonic plates There is one major difference between these two mountain ranges, and in this investigation you will examine this 4 Bathymetric map major difference. 4 Research materials The Andes - 4 Internet An oceanic plate/continental plate subduction zones Earth’s tectonic plates Subduction zone of one oceanic plate can move apart, or they and one continental plate can move toward one another. When they move toward one Andes Mountains, Peru another they collide with an almost unimaginable force. Often these collisions go on for millions of years and slowly produce mountains. When the conditions are just right, truly massive mountain ranges can be produced by converging plates. Locate the Andes on your bathymetric map. Identify the location of the Nazca Plate and the South American Plate as well. a. What does the term “subduction” mean? b. What happens to the tectonic plate that subducts under another plate? c. How does subduction produce mountains? d. What do you think is causing the Nazca Plate to subduct under the South American Plate? South American Nazca Plate South American e. How do buoyancy and density affect the subduction event Plate that has produced the Andes mountains? Oceanic plate, basalt, denser, less buoyant, sinks under the f. How do the density of the Nazca Plate and the South continental plate American Plate compare? Continental plate, andesite and granite, less dense, more buoyant, floats The Himalayas - above the oceanic plate When two continental plates collide The Himalayas are the tallest mountain range in the world. They are the result of two continental plates converging. The Indo-Australian Plate is slamming into the enormous Eurasian Plate and the result is a vast collection of the world’s tallest peaks. The Himalayas are a relatively young mountain range, and are in fact growing every day. The process that created them is similar to that which produced the Andes but with one major difference; both plates are continental plates. As the two plates collide, parts of both plates have folded and been uplifted. Prior to the collision, and ancient oceanic plate subducted under the Eurasian plate and began the uplifting process. The Indo-Australian Plate Investigation 9.3 Earth’s Two Major Mountain Ranges 83 CHAPTER 9 • Plate Tectonics is following that ancient plate What happens when two continents collide? under the Eurasian plate, but since the two continental plates Continent are about the same density the Continent Indo-Australian Plate is slamming into, scraping, and uplifting the Eurasian Plate as it is forced S under. The ancient oceanic plate ubdu ctin g o was more dense than the Eurasian cea nic plate, so it slid under without pl ate the massive collision taking place now. As the Indo-Australian Plate slammed into the massive Eurasian plate, the two crumpled on their contacting edges, producing the many parallel ridges of the Himalayan Range. These are called fold mountains. The massive force of these two plates coming together is forcing the Indo-Australian Plate to reluctantly subduct under the Eurasian plate, and this is causing continuing uplift to the range. Thinking about converging plates Himalayan Mountains Eurasian a. Why is the Indo-Australian Plate resisting subduction so much Plate and not simply sliding under the Eurasian plate, like the Nazca Plate is sliding under the South American Plate in the subduction zone that has created the Andes? b. What do you think is responsible for moving the Indo-Australian Plate thousands of miles over millions of years? India c. Use your hands to model the collision between the today 10 mya Indo-Australian Plate and the Eurasian Plate. 38 mya 55 mya Indian Use your fi ngers to create the Himalayan Mountains similar to Ocean 71 mya how the Eurasian Plate is folding and being uplifted by the Indo-Australian Plate. d. The Peru–Chile Trench, also known as the Atacama Trench, is Indo-Australian Plate a deep-ocean trench in the eastern Pacifi c Ocean. It is located “India” about 160 km (100 mi) off the coast of Peru and Chile. At its landmass deepest point, it is 8,065 m (26,460 ft) below sea level. Use the mya = Millions of years ago concept of subduction to explain its existence. 84 Unit 3 Earth’s Systems CHAPTER 9 • Plate Tectonics e. On your bathymetric map locate another likely oceanic plate and continental plate subduction zone. What would be the clues you would look for? What did you find? Use the Internet and other research materials to see if you are correct in your prediction of the location of another likely oceanic plate and continental plate subduction zone. f. On your bathymetric map locate another likely location of two continental plates coming together. What would be the clues you would look for? What did you find? Use the Internet and other research materials to see if you are correct in your prediction of the location of another likely oceanic plate and continental plate subduction zone. g. Challenge: The Peru–Chile Trench is the ninth deepest oceanic trench in the world. Marianas Trench is the deepest. Research this trench and propose a reason why it is deeper than the Peru–Chile Trench. Bonus: Two plates are converging to form the Marianas Trench. One is the Pacific Plate. What is the other? Can you explain why the Pacific Plate is the one subducting? Investigation 9.3 Earth’s Two Major Mountain Ranges 85.

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