Investigating Plate Tectonics, Earthquakes, and Volcanoes
INVESTIGATING PLATE TECTONICs EARTHQUAKES AND VoICANOE At their edges the plates interact with each other in one of three ways they con verge diverge or slip past each other When two oceanic plates converge or come together the older denser plate slides under the younger plate When oceanic crust meets denser continental crust the oceanic crust slides underneath In other places plates diverge or spread apart In the middle of the oceans long ridges form where plates diverge Magma or molten rock rises from the man tle and fills in the gap creating new seafloor On the continents diverging plates create troughs called rift valleys The most extensive of these is East Africa s Great Rift Valley Along some boundaries two plates neither converge nor diverge instead they slide past each other along fractures in the crust These fractures are called transform faults The plates sometimes stick causing a buildup of pres sure that may be released in the form of an earthquake The sudden and sometimes vio lent shaking caused by earthquakes kills about IO 000 people a year Approximately 80 per cent of the world's earthquakes occur in the Ring of Fire a belt circling the Pacific Ocean that traces the boundaries of tectonic plates The Pacific Ring of Fire is also the site of about 90 percent of the world's
INTRODUCTION Volcanoes are vents in Earth's surface through which molten rock gas and ash erupt The name is perhaps more com monly used for the mountains formed by the buildup of material erupted from these vents The most prevalent type of volcano is the stratovolcano a steep cone shaped mountain made up of layers of rock frag ments and hardened lava Japan's Mount Fuji is a classic example of a stratovolcano Shield volcanoes are another common type Typical of Hawaii they are dome shaped mountains formed by the accumulation of broad lava flows Volcanoes earthquakes mountain building these fundamental phenomena of Earth science can all be explained by plate tectonics The theory provides invaluable insight into the processes that have shaped the face of the planet over many millions of years But understanding the movements of Earth's crust can have more immediate and tangible benefits as well For instance experts are using technology to try to predict earth quakes and volcanic eruptions and to create buildings that can withstand the deadly force of earthquakes Their work may be able to help more people survive tectonic catastro phes like the explosion of Mount Merapi
PLATE TECTONICs The modern of the theory motions of Earth's outer layers is called plate tectonics It provides a framework for understanding many of Earth's features such as mountains earthquakes and vol canoes as well as the distribution of fossils and the ages of rocks It also helps scientists reconstruct ancient climates and continental configurations BASICS OF THE THEORY In 1912 the German meteorologist Alfred Wegener proposed that the continents had once been joined as a gigantic land mass called Pangea also spelled Pangaea According to this theory called continen tal drift the supercontinent long ago broke into pieces the present continents which have since drifted to their current posi tions At the time many geologists rejected Wegener s ideas partly because he had no convincing explanation why continents would move Io
