61 terms

Earthquakes, Volcanism, and Plate Tectonics

what is wegener's continental drift hypothesis?
The continents cut/ drag thorugh the ocean floor, moving around earth's surface.
what evidence did wegener use to make his hypothesis (4 things)
1:fit of the continents 2:fossil evidence
3:evidence from rocks 4:climatic evidence
what is the modern theory of plate tectonics?
earths fragmented lithosphere is in constant motion because of the plasticity of the underlying asthenosphere to to mantle heat.
how do the continental drift hypothesis and the theory of plate tectonics differ?
it is not thought that the continents move WITH th ocean floor, not through it.
what device tells us information about the sea floor?
how did information about the sea floor develop the modern tectonic plate theory?
geomagnetic reversals show sea floor spreading, as do ocean trenches, ridges, and volcanoes. the sea floor is moving too, not JUST the continents.
how does ocean floor topography tell us about continental drift theory?
new sean floor forms out of magma upwelling in mid-ocean ridges (mountain chains in the middle of the ocean floor).
how does the age(s) of the ocean floor tell us about continental drift theory?
the ocean floor is youngest along the area along the mid-ocean ridge. it is oldest at the sudbuction zones near plate boundaires. none of the ocean floor is older then 180 million years old (any older than that has already subducted).
how do geomagnetic reversals tell us about continental drift theory?
new forming rocks match earth's polarity as they form. when they are cooled, their polarity can NOT change. however, earths magnetism changes, and so there are stripes in the ocean floor of north and the souh polarity in the rock.
how are the location of volcanoes evidence of plate tectonics?
volcanoes form at convergant subduction boundaries, which only occur because of plate movement. also, volcanics are formed because of rising magma in the mantle, which is also the cause of plate tectonics.
how are earthquake locations evidence of plate tectonics?
earthquakes only occur as a result of movement AT plate boundaries, which occurs beacause of plate tectonics.
why do deep earthquakes originate under continents?
deep earthquakes form only at subduction boundaries. these occur at ocean-continent boarders. as the plate subducts, it gets deeper and deeper into earth. this means than the deepest, strongest earthquakes occur under continents.
how do hotspot island chains form?
a plume of hot mantle causes volcanoes to be built right above them (in the middle of the ocean). as the ocean floor moves, more and more volcanoes form, and this creates a chain of volcanoes.
how are hotspot island chains evidence of plate tectonics?
the CHAIN of islands occurs because of the movement of the ocean floor.
what is polar wandering?
evidence of lava flows show that the north pole has moved over time. however, in europe, the lava flows shoe DIFFERENT locations of the north pols, makeing TWO north poles! the north pole hasn't moved though, and there were never two-- the CONTINENTS have moved.
how is polar wandering evidence of plate tectonics?
the north pole hasn't moved, and there were never two-- the CONTINENTS have moved. if we line up the movement of the continents, the locations of the north pole match!
what is normal polarity?
when the magnetism of earth is towards the north pole.
what is reverse polarity?
when the magnetism of earth is towards th south pole.
how is polarity evidence of plate movement?
new forming rocks match earth's polarity as they form. when they are cooled, their polarity can NOT change. however, earths magnetism changes, and so there are stripes in the ocean floor of north and the souh polarity in the rock.
contrast oceanic and continental crust.
oceanic crust is more dense, and has a basaltic composition. continental crust is less dense an has a granitic composition.
what are the characteristics of lithosphere?
rigid solid broken into many pieces called tectonic plates. made of the crust and the top of the mantle.
How does the lithosphere affect plate to plate motion?
densest lithosphere always subducts under less dense lithosphere. lithosphere is less dense than asthenosphere, so it moves on top of it.
how do oceanic vs continental crust affect plate motion?
oceanic lithosphere is less dense than continental lithosphere, so it will always be the one subducting.
what is the aesthenosphere?
plastic solid capable of flow. composed of the only rock in the mantle (top part of the mantle).
what are divergant boundaries?
plates move apart and the gap fills with molten rock.
what are convergant boundaries?
(L-L) 2 plates collide with each other and are pushed upwards.
(O-L) plates collide and denser ceanic plate subducts into mantle, causing magma to rise.
(O-O) denser ocean (OLDER) subducts under and creates volcanic activity.
what are transform boundaries?
plates slide past each other
what do convergant boundaries create?
(L-L) mountains
(O-L) deep ocean trench, continental volcanic arc
(O-O) vlcanic island arc
what do divergant boundaries create?
new sea floor, rift valleys.
what do transform boundaries create?
earthquakes and transform faults.
examples of divergant boundaries are?
Mid- Atalantic Ridge
examples of convergant boundaries are?
(L-L) Himalyas
(O-L) Andes Mountains
(O-O) Japan
examples of transform boundaries are?
San Andres Fault
where do deep sea trenches form (boundary-wise)? why?
at convergant-subduction boundaries. the subducting plate drags the top plate down with it, causing a deep, narrow trench in the ocean floor.
where do tsunamis occur? why?
at convergant- subduction boundaries. when the top plate is dragged down by the subducting one, it will eventualy snap back into it's original shape, causing the water that was in the trench that was once there to be pushed outwards.
what causes volcanism?
increase in temperature or decrease in pressure.
what are the tree types of volcanically active regions? whay are they active?
divergant boundaries-- decrease in pressure
convergant subduction- subducting plate melts and decreases pressure.
hotspots- cause magma to well to the surface
what are the 2 kinds of lava? how do they differ?
felsic/granitic: quartz, feldspar, mica; sedimentary rock; continental crust; very viscous; volcanic dome.
mafic/basaltic: pyroxine, olivine, amphibole; oceanic crust; less viscous; shelid, basalt plateau, cinder cone.
what are the 3 (or 4) kinds of volcanoes? describe each and give examples.
sheild: low sloping sides, largest, basaltic lava, quiet eruption, on ocean floor, Hawaii and Iceland.
composite cone: ocean-land subduction, steep slope, tall, andesitic lava, violent eruptions, takes 1000's of years to form, Mt St Helens and the Andes.
cinder cones: no lava, short eruptions, gas and magma build up and instantly form volcano, smallest, steep slope.
(lava plateu: fissure eruption causes flood of lava).
what are the 2 kinds of lava? describe each.
pahoe hoe: ropey, fast flowing, cools quickly.
aa: blocky, sharp, slow flowing, cools slowly.
what are the 4 different pyroclastic materials? describe each.
blocks: largest, piece of volcano flies off side.
lapilli/cinder: 2nd smallest, walnut sized.
ash: smallest
bombs:lava shoots through and dries in the air (football shaped).
what is the composition of gas released from a volcano?
70% water, 15% CO2, 5% nitrogen, 5% sulfur
what are the dangers of volcanism?
pyroclastics (ash, blocks, and bombs), lahars/ mudflows, pyroclastic flow (*most dangerous*mix of gas and hot ash)
what are warning signs that a volcano will erupt?
small earthquakes, release of gas and/or ash
how do mountain belts form?
(L-L) conversion boundaries. because they are less dense then the asthenosphere, they can't subduct, so they push against each other, forcing each other upwards.
what is an earthquake?
the movement of plates caused by a build up of stress/ energy
what causes earthquakes?
pressure and tension put stress on a rock, causing it to release seismic energy, rupturing and moving it.
what is the epicenter of an earthquake?
where the energy reaches earth's surface-- directly above the focus.
what is the focus of an earthquake?
the origin of the seismic energy-- where the plate breaks.
what are faults?
break/ crack it a rock where movement occurs.
what is used to record earthquakes?
what is a seismogram?
a recording of an earthquake
what are p waves? (speed, travel style, what can it move through, destructiveness, origin)
primary waves, push-pull movement, faster, goes through solid, liquid, and gas. not destructive, come from focus
what are s waves? (speed, travel style, what can it move through, destructiveness, origin)
secondary waves, move up and down, slower, can only go through solids. non-destructive, come from focus.
what are surface waves? (speed, travel style, destructiveness, origin)
slowest, like pebble hitting pond, VERY destructive, comes from epicenter
what are the dangers of earthquakes?
collapsing structures, tsunamis (but only @ convergant subduction zones), landslides (loss of friction), liquifaction (loose sediment turns into quicksand-like liquid and then settles)
how do we know about earth's interior?
volcanic eruptions (magma), meteors with similar composition
describe the crust.
granite, basalt. sedimentary rock
describe the mantle.
solid. ultramafic (low silica) igneous rock.
describe the outer core.
liquid metal, blocks s waves, causes magnetic field. nickle and iron.
describe the core.
solid due to intense pressure (even though it has a VERY VERY high temperature). nickle and iron.