The Earth’s external shell, the lithosphere, consists of the crust and also uppermost mantle, is separated into a patchwork of big tectonic bowl that relocate slowly relatively to every other. There are 7-8 significant plates and many young plates. Varying between 0 to 100mm every year, the motion of a bowl is propelled by convection in the underlying hot and viscous mantle.
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Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate limits in area that may be anything from a couple of kilometres come a few hundred kilometre wide. To clock a simulated fly-by along brand-new Zealand"s bowl boundary examine out this video.
There space three main varieties of key boundaries:
1. Convergent boundaries: where 2 plates room colliding.
Subduction zones happen when one or both of the tectonic plates are composed that oceanic crust. The denser key is subducted under the less thick plate. The bowl being forced under is eventually melted and also destroyed.
i. Whereby oceanic late meets s crustIsland arcs and also oceanic trenches happen when both the the plates space made the oceanic crust. Zones of active seafloor spreading can likewise occur behind the island arc, recognized as back-arc basins. These room often linked with submarine volcanoes.
ii. Whereby oceanic late meets continent crustThe denser oceanic key is subducted, often developing a mountain selection on the continent. The Andes is an example of this form of collision.
iii. Wherein continental late meets continental crustBoth continental crusts room too light to subduct for this reason a continent-continent collision occurs, developing especially big mountain ranges. The most spectacular instance of this is the Himalayas.
2. Divergent boundaries – where two plates are moving apart.
The space created can additionally fill with new crustal product sourced indigenous molten magma that develops below. Divergent limits can kind within continents however will eventually open up and become ocean basins.
i. On landDivergent boundaries within continents initially create rifts, which create rift valleys.
ii. Under the seaThe most active divergent plate boundaries are in between oceanic plates and are often dubbed mid-oceanic ridges.
3. Transform boundaries – wherein plates on slide passed every other.
The relative activity of the bowl is horizontal. Lock can occur underwater or ~ above land, and crust is neither ruined nor created.
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Because that friction, the bowl cannot simply glide past each other. Rather, stress and anxiety builds up in both plates and also when the exceeds the threshold of the rocks, the energy is exit – leading to earthquakes.