Geography - Plate Tectonics and Structure of the Earth

Plate tectonics + Structure of the Earth

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The Structure of the Earth

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The crust is the outer layer of the earth. It is a thin layer between 0-60 km thick. The crust is the solid rock layer upon which we live. The mantle is the widest section of the Earth. It has a thickness of approximately 2,900 km. The mantle is made up of semi-molten rock called magma. In the upper parts of the mantle the rock is hard, but lower down the rock is soft and beginning to melt. It is around 5000°C. The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. It is still extremely hot, with temperatures similar to the inner core. The inner core is in the centre and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500°C.

Continental Crust Vs Oceanic Crust

Continental Crust: The surface of the earth that is found on the continents It has a thickness of around 25-70km It is less dense than the oceanic crust - around 2.7g/cubic cm Continental crust is not recycled Continental crust is mainly made from granite

Oceanic Crust: Oceanic crust is usually found on the floor of the oceans It has a thickness of around 7-10km It is more dense than continental crust - 2.9g/cubic cm Oceanic crust is recycled - when it subducts, it melts and forms new land It is mainly made from basalts

Oceanic Crust:  

What is a volcano?

Volcanos are openings in the crust, from which magma, gas and lava explodes. When magma rises through cracks, pressure builds up and magma erupts as lava and forms new rock on the ground. The magma chamber contains magma - the vent allows magma to escape. The crater is created when the top is blown off in an eruption. Shield Volcanos: Shield volcanoes are usually found at constructive boundaries. They are low, with gently sloping sides. They are formed by eruptions of thin, runny lava. Eruptions tend to be frequent but relatively gentle. Composite Volcanos: Composite volcanoes are made up of alternating layers of lava and ash (other volcanoes just consist of lava). They are usually found at destructive boundaries. The eruptions from these volcanoes may be a pyroclastic flow rather than a lava flow.

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Primary + Secondary Effects of Volcanos

Lahar: a mudflow that is formed from the mixture of debris, ash and water. This water comes from excessive precipitation, eruptions melting snow/ice or water having being ejected from a crater lake. Tsunami: Can be triggered by a landslide down a volcano's side displacing a large amount of water, or a volcanic eruption under water. Ash and tephra fall: ash = <2mm. It is formed from pulverised lava/rock. Lava flow: the molten rock emitted by the volcano when it erupts. It can move very slowly so does not often directly cause deaths. Ash cloud: it consists of fragments of pulverised rock, minerals and volcanic glass, created during volcanic eruptions. Pyroclastic flows: hot poisonous gases such as CO2 and SO2, steam and ash that flows up to 100km/hour down a volcano's sides. It can reach a temperature of up to 1000°C. Forest fires: caused by hot lava flows and pyroclastic flows. Temporary temperature changes: ash emitted reflects solar rays in the atmosphere.

Primary Effects: Effects that have occurred as a direct result of the natural hazard Secondary Effects: Effects that have occurred as a result of the primary effects Primary effects of Volcanic Eruptions: Ash and tephra fall, lava flow, ash cloud, pyroclastic flow Secondary Effects of Volcanic Eruptions: Lahar, tsunami, forest fires, temporary temperature changes

4 types of plate boundary:

Destructive (convergent) plate boundary: two plates come together. The oceanic crust subducts below the continental crust. As the oceanic crust is full of carbon, it makes the magma gaseous, so it rises, forming volcanoes. Also, the oceanic crust still exerts a force on the continental crust, forming fold mountains. Constructive (divergent) plate boundary: two plates pull apart. The convection currents have rising limbs pushing up against the crust, creating ridges (e.g.: mid-Atlantic ridge). This also creates gentle volcanoes. Collision plate boundary: two continental plates collide with each other. Neither plate is forced under the other, so they are forced  up and form fold mountains. Conservative plate boundaries: The plates move either both in the same direction, or in different directions, at different speeds. Friction is suddenly overcome, and the plates quickly slide past each other, causing earthquakes.

Destructive (convergent) plate boundaries

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Constructive (divergent) plate boundaries

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Collision plate boundaries

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Conservative plate boundaries

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