Transcript Ch 18 PP
CHAPTER 18 Plate Tectonics • Three factors cause the movement of Earth’s tectonic plates: mantle convection, ridge push, and slab pull. • Forces at plate boundaries produce landscape features such as mountains, trenches, and island arches. CHAPTER 18 Plate Tectonics • The interactions of tectonic plates cause volcanoes and earthquakes. • Earthquakes send waves through Earth. CHAPTER 18 Plate Tectonics Activity • Consider a pot of water sitting on a hotplate. Using your knowledge of convection (Ch.14), draw a labelled diagram and use arrows to indicate the rising of warm, less dense water and the falling of cool, more dense water. • What would happen if you placed a cork in the middle of the pot of water? Would it move or stay in the middle? Why? What force is acting between the water and the cork causing the cork to move? • The cork floating on the water is analogous to Earth’s crust “floating” on the mantle. Read page 517 to learn how mantle convection currents can move tectonic plates. CHAPTER 18 Plate Tectonics Key Ideas • Three factors cause the movement of Earth’s tectonic plates. • Forces at plate boundaries produce landscape features. • The interactions of tectonic plates cause volcanoes and earthquakes. • Earthquakes send waves through Earth. 18.1 Causes and Effects of Plate Movement • Scientists now believe that three forces work together to move the tectonic plates: 1. mantle convection 2. ridge push 3. slab pull VOCABULARY mantle convection ridge push slab pull 18.1 Causes and Effects of Plate Movement • Uplifted mountains, volcanic belts, and island arcs are found parallel to convergent boundaries. • Ocean trenches lie along convergent boundaries. • Mid-ocean ridges and rift valleys mark divergent boundaries. VOCABULARY mantle convection ridge push slab pull 18.2 Geological Events • Volcanoes are produced over lithosphere cracks and mantle hot spots. • Hot spots are rising plumes of hot mantle magma. As tectonic plates move over the hot spot, a chain of progressively younger volcanoes is formed opposite to the direction of plate movement. • Volcanic island chains and volcanic belts are created on the overriding plate, parallel to a convergent boundary. VOCABULARY volcano hot spots volcanic belt volcanic island arc earthquakes fault focus epicentre shallow-focus intermediate-focus deep-focus seismic wave body wave primary wave (P–wave) secondary wave (S–wave) surface wave 18.2 Geological Events • Earthquakes result when tectonic forces overcome the friction between plates. Earthquakes are categorized based on how far beneath the surface the focus is located. • The sudden movement of the lithosphere during an earthquake sends seismic waves (vibrations) through Earth. • Primary and secondary body waves travel through Earth, starting at the focus, the site of the earthquake within Earth. • Surface waves travel along the outside of Earth. They cause the most destruction. VOCABULARY volcano hot spots volcanic belt volcanic island arc earthquakes fault focus epicentre shallow-focus intermediate-focus deep-focus seismic wave body wave primary wave (P–wave) secondary wave (S–wave) surface wave