All about volcanoes . This power point is about volcanoes.You will be learning where they are located ,how they formand you will see pictures and diagrams of volcanoes. Youwill also be learning different kinds of volcanoes. HAPPYLEARNING!!!!!!!!!
LOCATIONSVOLCANOES OCCUR IN DESIGNATEDNARROW BANDS.BUT WHY??????NOBODY KNOWS THAT YET. BUT WE DOHAVE A CLUE . An important clue tounderstanding volcanoes is knowing thelocation of the volcanic bands. Many of theworlds active volcanoes are located aroundthe edges of the Pacific Ocean: the WestCoast of the Americas; the East Coast ofSiberia, Japan, the Philippines, andIndonesia; and in island chains from NewGuinea to New Zealand--the so-called "Ringof Fire" (diagram to left). Recently, activevolcanoes were also found in Iceland, theKenya Rift Valley in Eastern Africa, Italy, andHawaii. Looking at the locations of thesevolcanoes through the glasses of platetectonics, we also notice that most volcanoesoccur near the edges of the large "plates" thatcomprise the solid surface of Earth. Lookingeven more closely, we also notice that thedangerous explosive volcanoes, such asMount St. Helens and Mount Pinatubo, thatmake the evening news are located whereplates are crunching together. Thequieter, "effusive" volcanoes, like Iceland andHawaii, are found mostly where plates arecoming apart or in the middle of a plate.
HOW VOLCANOESFORMDeep inside Earth, between themolten iron core and the thin crustat the surface, there is a solid bodyof rock called the mantle. Whenrock from the mantle melts, movesto the surface through thecrust, and releases pent-upgases, volcanoes erupt. Extremelyhigh temperature and pressurecause the rock to melt and becomeliquid rock or magma. When alarge body of magma has formed, itrises thorugh the denser rock layerstoward Earths surface. Magmathat has reached the surface iscalled lava.
DIFFERENT KINDSOF VOLCANOESTHERE ARE MANY KINDS OFVOLCANOES. CINDERCONE,COMPOSITE ,ANDSHIELD VOLCANOES ARE THEKINDS OF VOLCANOES.
CINDER CONECinder cones are the simplest typeof volcano. They are built fromparticles and blobs of congealedlava ejected from a single vent. Asthe gas-charged lava is blownviolently into the air, it breaks intosmall fragments that solidify andfall as cinders around the vent toform a circular or oval cone.
COMPOSITEVOLCANOESSome of the Earths grandestmountains are composite volcanoes--sometimes called stratovolcanoes.They are typically steep-sided, symmetrical cones of largedimension built of alternatinglayers of lava flows, volcanicash, cinders, blocks, and bombs andmay rise as much as 8,000 feetabove their bases. Some of the mostconspicuous and beautifulmountains in the world arecomposite volcanoes, includingMount Fuji in Japan, MountCotopaxi in Ecuador, Mount Shastain California, Mount Hood inOregon, and Mount St. Helens andMount Rainier in Washington.
Shield volcanoesShield volcanoes, the third type ofvolcano, are built almost entirely of fluid lavaflows. Flow after flow pours out in alldirections from a central summit vent, orgroup of vents, building a broad, gentlysloping cone of flat, domical shape, with aprofile much like that of a warriors shield.They are built up slowly by the accretion ofthousands of highly fluid lava flows calledbasalt lava that spread widely over greatdistances, and then cool as thin, gentlydipping sheets. Lavas also commonly eruptfrom vents along fractures (rift zones) thatdevelop on the flanks of the cone. Some ofthe largest volcanoes in the world are shieldvolcanoes. In northern California andOregon, many shield volcanoes havediameters of 3 or 4 miles and heights of 1,500to 2,000 feet. The Hawaiian Islands arecomposed of linear chains of these volcanoesincluding Kilauea and Mauna Loa on theisland of Hawaii-- two of the worlds mostactive volcanoes. The floor of the ocean ismore than 15,000 feet deep at the bases of theislands. As Mauna Loa, the largest of theshield volcanoes (and also the worlds largestactive volcano), projects 13,677 feet above sealevel, its top is over 28,000 feet above thedeep ocean floor.