Investigating Plate Tectonics, Earthquakes, and Volcanoes
INTRODUCTION Nhe tropical island of Java Indonesia has sweeping beaches lush landscapes and majestic mountains But in late 2010 the eruption of Java's Mount Merapi volcano made parts of the island an ugly nightmare Huge gas clouds and fiery rocks spewed high into the air Glowing lava snaked down the mountainside Showers of ash draped homes and fields in ghostly gray Later search and rescue teams hunted for survivors but found mostly bodies some charred caught in mid flight In the end hundreds of peo ple were killed This powerful eruption is just one illustration of why many Earth scientists focus on the study of plate tectonics Plate tectonics is the modern theory of the movement of Earth s outer shell or lithosphere The lithosphere consists of the planet s rocky surface layer called the crust and the solid outermost layer of the mantle beneath The lithosphere is broken into about a dozen large plates and several smaller ones The plates float on a much hotter layer of par tially molten rock called the asthenosphere which is also part of the mantle The asthenosphere slowly churns driven to movement by radioactive heating of the planet s core This churning causes the plates of the lithosphere to move at a rate of about 2 to 4 inches 5 to 10 centimeters a year
INTRODUCTION Thick smoke rises from the Mount Merapi vol cano on the island of Java Indonesia on Oct 26 2010 AFP Getty Images
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
