How Does Plate Tectonics Work?
Where the plates meet is where interesting things happen: volcanoes, earthquakes, and sea-floor spreading. What happens depends on how the plates are moving relative to each other. For example, they could be moving away from, towards, or sliding against each other.
Plate geography
The surface of the earth is covered by . They move continuously but at different rates. Boundaries, however, are not fixed; plates spread apart and plates weld together. Most plates are composed of some oceanic crust and some continental crust. The Pacific plate is the largest and is composed almost entirely of oceanic crust. No plate is composed entirely of continental crust.
Plate boundaries
Divergent-Where plates split and pull apart due to tensional forces.
Convergent-Where plates collide due to compressional forces.
Transform-Where plates slide past each other due to shear stress.
Where are they going and how fast?
There is no fixed pattern to their movement. The plates are moving in all directions at rates ranging from 1 to 18 cm per year.
Why are the plates moving?
Traditionally, plate movement has been explained as being the result of convection in the mantle. Heat escapes from the center of the earth causing the mantle to overturn. The result is convective cells on which the crust could potentially be carried.
More recently however, geologist have suggested that the plates actually move themselves and may in part cause mantle convection! Three possible mechanisms have been suggested:
Slab pull
As the lithosphere cools it becomes more dense. Eventually it is more dense than the asthenosphere it rides above and it sinks. It pulls the lithosphere behind it in towards the mantle.
Ridge push
Young, 'warm' rock generated at the mid-oceanic ridges is less dense and sits higher in the asthenosphere than older, 'cooler' rock. Gravity makes the lithosphere slip off the elevated ridge.
Trench suction
Steeply sinking plates will suck the adjacent plate towards the trench.
Tectonic Plates
Plates
The Earth’s crust is made up of seven principal tectonic plates and numerous other smaller plates. The plates are sections of the crust that “float” on the mantle, which is made up of molten rock. Where the plate’s meet, huge forces mean that they can form features such as volcanoes, fold mountains, deep-sea trenches and earthquakes.
There are two main types of tectonic plate. Oceanic crust is often only about 5km thick, but is very dense. Continental crust is considerably thicker, often being approximately 30km deep, but is less dense.
Convection Currents
The Earth’s Tectonic Plates all move very slowly on the mantle, meeting along the four main boundaries that can be found in the next section. The plates move due to convection currents in the mantle. These are hot currents of molten rock that slowly move within the mantle and cause the plates above
Geology and seismic waves project
by Izi and Han 10f
