14.1 Flashcards

Question

concentration of earthquakes

Answer 1

1920s several prominent earthquake zones identifies parallel to trenches zones became known as Wadati and Benioff establishment of WWSSN allowed seismologists to map zones precisely reveals plate boundaries

Answer 2

plates are moving apart magmas rises through asthenosphere due to convection currents moving in opposite directions due to intense heat produces mid ocean ridges at 2.5km below the surface ridges break not continuous and break into intervals and segments forms pillow lavas forms volcanic islands causes chemical changes in balsatic rocks as dea water seeps into rifts and is superheated

Answer 3

magma erupting onto sea bed cools quickly, forming rounded mounds

Answer 4

mid ocean ridges are produced by overlying rocks being forced up into a dome as magma rises up to the surface the rigid lithoshere is placed under great stress and fractures along parallel faults eg Iceland

Answer 5

rift zomes are not confined to the ocean floor they also occur on land and explain how continents break up eg rift stretching from Red Sea towards Turkey sometimes where the crust has been stretched faulting is caused and a sunken valley known as a graben in created rift widens and magma erupts as the surface if magma continues to well up, a new spreading boundary will form

Answer 6

oceanic continental continental continental oceanic oceanic

Answer 7

denser oceanic plate is forced under the continental plate subduction causes the deepening of the ocean at the plate boundary and forms an ocean trench - long narrow depressions with depths of 6000-11000m normally asymetric layers of sediment and sedimentary rock develop on oceanic plates adjacent to continents rocks crumple and drag across continental plate forming mountain chains such as the Andes oceanic plate subducted at 30-70 degrees fractures in Benioff zone oceanic plate melts and rises to surface as plutons of magma creating further uplift of fold mountains

Answer 8

slightly denser one subducts creating a trench as magma rises, forming chains of volcanic islands eg North American plate subducted underneath Carribean plate forms antilles eg Mariana trench is partly formed from this

Answer 9

little if any subductions takes place as htey have simalar densities eg collision of african and eurasian plates created the alps

Answer 10

plates slide past each other in a shearing motion no volcanic activity frictional resistance to movement along the palte boundaries often causes a build up of pressure causes rocks to fracture releasing a lot of energy as earthquakes doesnt produce landforms tears landscape if rocks are exposed at surface movement between strata may be visible drainage modified as river courses are deflected by movements eg california san andreas fault

Answer 11

shape type of eruption

Answer 12

shield volcanoes may erupt along lines of fissures rather than a central vent spilling liquid lava in successive layers form broad plateaux such as the Colombia plateaux - often cut by deep canyons that expose the layers of rock - Grand Canyon extensive lava flow are basaltic in nature so they can they can flow great distances flat and featureless macrofeature

Answer 13

3-4 miles wide and 1500-2000m tall eg Mauna Loa built up slowly by accreation of thousands of flows of highly fluid basaltic low silica so spreads over wide areas cools as thins forming gently dipping sheets lava erupts form rift vents along fractures that develops on the flanks of the cone magma has low gas content and is low in silica allowing it to flow over wide distances

Answer 14

craggy, steep sloped convex sides covered with rock debris typically found near large composite volcanoes made of layers of lava formed by repeated violent eruptions and slow moving lava flows which gives layered structure magma is made of higher silica and high gas pressure making magma slow moving and explosive eg Puy region of central france

Answer 15

formed from ash, cinders and volcanic bombs ejected from crater sides are steep and symmetrical eg Patricutun, Mexico may occur as single volcanoes or secondary volcanoes on the sides of stratovolcanoes or shield volcanoes tephra ejected lava cools and builds up around the vent forming crater build up over time

Answer 16

tall and conical built up from many layers of hardened lava, tephra, pumice and volcanic ash steep profiles periodically explosive and quiet eruptions lava typically cools before spreading due to high viscocity layered structure built up of sequential outpourings of eruptive materials increase in temp causes dome to expand while its outer lava cools, causes newly hardened surface to splinter causing loose debris to fall from its sides eg Mt Et na

Answer 17

bowl shaped