Tectonic Plates
The Earth's crust is split into 14 segments known as tectonic plates. They are categorised into 'oceanic' and 'continental' crusts, which have different densities. Convection currents within the Earth's mantle cause these tectonic plates to move at slow rates. For example, the Pacific plate is currently drifting north-westwards by 6cm per year. Tectonic plates often collide or grind against one another, which causes different types of margins: constructive, destructive, collision and conservative.
Constructive margin: Where two plates move away from each other, causing magma to rise from the mantle, which cools to form ridges e.g. the Mid-Atlantic Ridge in the Atlantic Ocean caused by the Eurasian and North American plates pulling away from each other.
Destructive margin: Where a continental and an oceanic crust collide front-on, causing the oceanic crust - which is more dense - to submerge under the continental crust, forming a subduction zone. The oceanic crust which is pushed under melts, whilst the force of the collision causes the continental crust to buckle and form fold mountains. Magma rises up through the mountains which creates a volcanic eruption e.g. the Andes on the edge of South America caused by the Nazca plate subducting under the South American plate.
Collision margin: Where two plates of the same type of crust (equal density) collide front-on. Because the plates can neither sink nor be destroyed, the impact of the collision causes the plates to buckle and form fold mountains e.g. the Himalayas in Asia caused by the collision between the Indian and Eurasian plates.
Conservative margin: When two plates slide past one another, and not necessarily in opposite directions e.g. the San Andreas Fault in North America caused by the Pacific and North American plates sliding past each other, the Pacific plate sliding at a higher speed/rate.
The tense friction and strong impact of tectonic movement causes the natural hazards known as earthquakes and volcanoes. Constructive margins produce earthquakes that are relatively less violent due to little collision between plates, and volcanoes are usually underwater. With collision and conservative margins, earthquakes are very violent as a result of forceful collision, slipping and grinding; volcanoes are quite rare since magma does not often rise through the crust. Destructive margins can be considered the most devastating of all, with extremely violent earthquakes and volcanoes, hence their name.
Constructive margin: Where two plates move away from each other, causing magma to rise from the mantle, which cools to form ridges e.g. the Mid-Atlantic Ridge in the Atlantic Ocean caused by the Eurasian and North American plates pulling away from each other.
Destructive margin: Where a continental and an oceanic crust collide front-on, causing the oceanic crust - which is more dense - to submerge under the continental crust, forming a subduction zone. The oceanic crust which is pushed under melts, whilst the force of the collision causes the continental crust to buckle and form fold mountains. Magma rises up through the mountains which creates a volcanic eruption e.g. the Andes on the edge of South America caused by the Nazca plate subducting under the South American plate.
Collision margin: Where two plates of the same type of crust (equal density) collide front-on. Because the plates can neither sink nor be destroyed, the impact of the collision causes the plates to buckle and form fold mountains e.g. the Himalayas in Asia caused by the collision between the Indian and Eurasian plates.
Conservative margin: When two plates slide past one another, and not necessarily in opposite directions e.g. the San Andreas Fault in North America caused by the Pacific and North American plates sliding past each other, the Pacific plate sliding at a higher speed/rate.
The tense friction and strong impact of tectonic movement causes the natural hazards known as earthquakes and volcanoes. Constructive margins produce earthquakes that are relatively less violent due to little collision between plates, and volcanoes are usually underwater. With collision and conservative margins, earthquakes are very violent as a result of forceful collision, slipping and grinding; volcanoes are quite rare since magma does not often rise through the crust. Destructive margins can be considered the most devastating of all, with extremely violent earthquakes and volcanoes, hence their name.
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<--- Convection currents in the mantle
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<--- Plate margins