plate tectonics

Question 1

why do tectonic plates move ?

Answer 1

1. convection currents are the movements of heat within mantle.material in mantle is heated by the core and expands,rises and spreads out beneath plates.
2. this causes plates to be dragged along and move away from each other
3. hot mantle material cools slightly and sinks,pulling plates along
4. sinking mantle material heats up again as it nears the core,and the whole process repeats
5. slab-pull force occurs when dense,sinking oceanic plate at subduction zone pulls the rest of the plates behind it
6. the subducting plates drives the downward-moving portion of convection currents
7. mantle material found away from subduction zone drives the rising portion of convection current.

Question 2

oceanic-oceanic divergence

Answer 2

1. diverging convection currents in the asthenosphere exert frictional drag on the underside of the overlying lithospheric plates,pulling them apart
2. when the two oceanic plates diverge,fractures are formed at the plate boundary.
3. magma rises at the zone of divergence,flows out onto the sea floor as lava,and cools and solidifies to create a ridge of new ocean floor. (mid oceanic ridge)
4. at various points along the mid oceanic ridge,magma builds up and solidifies to form undersea volcanoes.when these volcanoes eventually grow above sea level,they are known as volcanic islands

Question 3

continental-continental divergence

Answer 3

1. two continental plates diverge when divergent convection currents in the underlying asthenosphere rises against underside of plates and spreads,exerting tensional stress
2. the continental plates are stretched and thinned,and the crust fractures on each side of the stressed area,separating into a sequence of fault blocks.
3. overtime,the fault blocks sink and a rift valley with adjacent block mountains are formed.As plates continue to diverge,a stepped rift valley will be formed
4. an inland lake might be formed if the valley accumulates rain water.
5. rift volcanoes are also abundantly formed as magma rises through thin and fractured cast

Question 4

oceanic-oceanic convergence

Answer 4

1. two oceanic plates converge when convection currents in the underlying asthenosphere sinks under the underside of plates,exerting compression stress.
2. when 2 oceanic plates converge,denser oceanic plate subducts under less dense oceanic plate.the area where this occurs is the subduction zone.
3. at the subduction zone,narrow and long depression in sea floor is formed due to bending of the oceanic crust,known as the oceanic trench
4. at the same time,denser subducting plate causes mantle material above it to melt,forming magma
5. magma rises through the crust to cool,solidify and build up as submarine volcanoes in ocean.overtime,submarine volcanoes may rise above sea level to form volcanic islands and a chain of volcanic islands called an island arcs is formed
6. earthquakes might also occur at plate boundary due to friction created between moving rock masses when a plate subducts under another

Question 5

continental-continental convergence

Answer 5

1. two plates converge when convergent convection currents in the underlying asthenosphere sinks under the underside of the plates,exerting compression al stress
2. when two continental plates converge,the plates resist subduction as both plates are too thick and buoyant for subduction to occur
3. as layers of rocks on the upper part of the crust are compressed together,the plates buckle and fold along fractures in the crust,folding upwards or sideways and forming fold mountains
4. earthquakes also occur at the plate boundary due to deformation of rock through process of faulting and folding

Question 6

oceanic-continental convergence

Answer 6

1. two plates converge when convergent convection currents in underlying asthenosphere sinks under underside of plates,exerting compressional stress
2. when the denser oceanic plate collides with the less dense continental plate,the oceanic crust subducts beneath the continental crust at the subduction zone
3. at the subduction zone,a narrow and long depression in sea floor known as oceanic trench is formed due to bending of oceanic crust
4. compressional force causes continental plate to be compressed,lifted and folded,forming fold mountains
5. the subduction at the denser plate causes mantle material above it to melt,forming magma which rises through the crust and cools and solidifies.The magma solidifies as either volcanoes or fold mountains.eventually,a chain of volcanoes called a volcanic arc may be formed
6. earthquakes may occur at plate boundary due to friction created between moving rock masses where plate subducts under another.prescence of volcanoes mean volcanic eruptions may occur at plate boundary.