Explain how plate movements cause volcanoes and earthquakes.?

Answer 1

Volcanos caused by plate motion are found near "subduction zones" where one plate is being driven under another plate. When the plate that is moving down is an oceanic plate large amounts of water are brought along with the plate -- this water lowers the melting point of surrounding rock creating pockets of magma. Since the liquid magma is less dense than the surrounding solid rock it migrates to the surface - creating volcanoes!

Do not think that plates just start melting because they move down into the asthenosphere - THIS IS NOT TRUE. Portions of the plate will melt because of the presence of water, not because the asthenosphere is hot enough to melt rocks. The asthenosphere is almost totally SOLID rock. It is just more dense than the lithosphere rock so the rock of the lithosphere "floats" on the asthenosphere. Subducting plates do not melt, they sink. They are cooler than the surrounding rock - thus they are more dense, and they sink.


Earthquakes caused by plate motion are a result of friction between two plates at their boundry. The plate is pushed with a relatively constant force, but will sometimes become stuck because of friction. The force pushing on this stuck portion of the plate will build up until it overcomes the force of the friction and suddenly all that stored energy is released at once and the plate jumps forward to where it would have been had it not become stuck. This releases seismic waves (s-wave, p-waves, love waves, and rayleigh waves), which cause the ground to move -- aka, an earthquake!

Some people seem to think earthquakes are most common at transform faults (plate boundries where plates slide past each other in oposite directions) - but that's not really true. Earthquakes are most common in areas near subduction zones. I'll link the USGS global seismicity map and a map showing plate boundries so you can see for yourself where earthquakes are most common.

Maps of seismic activity:
http://earthquake.usgs.gov/regional/world/seismicity/index.php
this one is a bit easier to see actually...
http://www.visionlearning.com/library/module_viewer.php?mid=66

Plate boundry map:
http://earthquake.usgs.gov/learning/topics/plate_tectonics/plates.php

Answer 2

Oceanic plates are mor dense than Continental plates. As such, when an oceanic plate and a contenental plate collide, the oceanic plate is forced under the contenental plate, where it is melted by the heat of the Asthenosphere. The contenental plate that assumes position on top of the oceanic plate forms mountains. The magma of the melted oceanic plate rises up into the contenental plate at it's weakest points. Volcanoes are formed by this magma that accumulates in a contenental plate. The area where any two plates are in contact, or where their borders lay is called a fault line. The forementioned scenario is that of a convergent fault line. Earthquakes are formed mainly at strike-slip fault lines. This is where two plate bounderies are parallel to each other, but they are moving in opposite directions. That is they are moving in a sideways fashion- not towords or away from each other. when the rocks on the two plate's edjes snag, they eventually break. When this happens a large amount of energy is released. imagine that you playing tug of war with another very close matched team. If they suddenly let go, your team will fall backwards. It is the same way with tectonic plate movement.

Answer 3

VOLCANOES

When two plates meet head on, one will often slide beneath the other.
This causes a build up of material beneath the second plate.
This additional material causes volcanoes to be formed on the second plate near the edge as a way is found to release the pressure.

EARTHQUAKES

When two plates are sliding past each other there is a lot of friction.
The plates tend to stick for a while until the build up in energy causes them to suddenly move causing an earthquake.
You can see a similar thing by pressing your hands together tightly. Then try to slide them. They will stick for a while and then release suddenly. This sudden jerking movement is analagous to an earthquake.

Answer 4

sure, volcanoes and earthquakes take position at places except plate obstacles. for instance: Kilauea and Mauna Loa volcanoes on the island of Hawaii are fantastically a lot interior the approach the Pacific plate and there are about 4000 earthquakes a year in Hawaii (maximum are very small and not at all felt by human beings).

Answer 5

Theres hot magma under these plates. Apart from the crust, the earth is made of a globule of molten rock. When the crust cracks on this floating lake, things pop out from the pressure. Sometimes the pressure causes earthquakes as the crust readjusts.

Answer 6

what they said