restless earth

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  • Created on: 10-06-12 11:50
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Tectonic plates
The Earth consists of four concentric layers: inner core, outer core, mantle and crust. The crust is made up of tectonic
plates, which are in constant motion. Earthquakes and volcanoes are most likely to occur at plate boundaries.
The structure of the Earth
The Earth is made up of four distinct layers:
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. With its immense heat energy, the inner core is like the engine room of the Earth.
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 mantle is the widest section of the Earth. It has a diameter 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.
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.
There are two different types of crust: continental crust, which carries land, and oceanic crust, which carries
The diagram below shows the structure of the earth. In geography, taking a slice through a structure to see inside is
called a cross section.
Cross section showing
structure of the Earth

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The Earth's crust is broken up into pieces called plates. Heat rising and falling inside the mantle creates convection
currents generated by radioactive decay in the core. The convection currents move the plates. Where convection
currents diverge near the Earth's crust, plates move apart. Where convection currents converge, plates move
towards each other. The movement of the plates, and the activity inside the Earth, is called plate tectonics.
Plate tectonics cause earthquakes and volcanoes.…read more

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Different plate boundaries
At a constructive boundary the plates move apart.…read more

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At constructive boundary the plates are moving apart. The plates
move apart due to convection currents inside the Earth.
The Helgafjell volcano on Westman Island, Iceland
As the plates move apart (very slowly), magma rises from the mantle.
The magma erupts to the surface of the Earth. This is also accompanied by earthquakes.
When the magma reaches the surface, it cools and solidifies to form a new crust of igneous rock. This process is
repeated many times, over a long period of time.…read more

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They are moving in a similar (though not the same) direction, at
slightly different angles and speeds.
As one plate is moving faster than the other and in a slightly different direction, they tend to get stuck.
Eventually, the build-up of pressure causes them to be released.
This sudden release of pressure causes an earthquake.
Volcanoes do not occur at conservative plate boundaries.…read more

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On a collision margin as the plates crash together the sediment goes up with them, becoming part of the
The rock layers get twisted together as they collide together.
An example of the fold mountains is the Alps.
Characteristics of the Alps
High mountain ranges, eg Mont Blanc, which is 4,810 m above sea level.
Glaciated valleys, eg the Rhone Valley.
Pyramidal peaks, eg the Matterhorn.
Ribbon lakes, eg Lake Como.
Fast-flowing rivers.
Contrasting microclimates on north facing (ubac) and south facing (adret) slopes.…read more

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Volcanoes form when magma reaches the Earth's surface, causing eruptions of lava and ash. They occur at destructive
(compressional) and constructive (tensional) plate boundaries.
The immediate effects of volcanic eruptions can be devastating, but they may be beneficial in the long term.
Key facts
A volcano is formed by eruptions of lava and ash.
Volcanoes are usually cone shaped mountains or hills.
When magma reaches the Earth's surface it is called lava. When the lava cools, it forms rock.…read more

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The magma chamber is a collection of magma inside the Earth, below the volcano.
The main vent is the main outlet for the magma to escape.
Secondary vents are smaller outlets through which magma escapes.
The crater is created after an eruption blows the top off the volcano.
An eruption occurs when pressure in the magma chamber forces magma up the main vent, towards the crater at
the top of the volcano.…read more

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There is little ash because it doesn't erupt as frequent because of less pressure building up.
A supervolcano is a volcano on a massive scale.…read more

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Earthquake energy is released in seismic waves. These waves spread out from the focus. The waves are felt most
strongly at the epicentre, becoming less strong as they travel further away. The most severe damage caused by an
earthquake will happen close to the epicentre.…read more


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