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Contents
I. Theory of Plate Tectonics
i. Geological Evidence
ii. Biological Evidence
iii. Earth's layers
II. Plate Margins
i. Constructive
(ia) Oceanic Ridges
(ib) Rift Valleys
III. Hotspots
IV. Vulcanicity
i. Volcanic eruptions
V. Intrusive landforms
i. Batholiths/laccoliths
ii. Dykes
iii. Sills
VI. Extrusive landforms
i. Basaltic lava
ii. Andesitic/rhyolitic lava
iii. Lava plateaux
iv. Basic/shield volcano
v. Acid/dome volcano
vi. Ash/cinder volcano
vii. Composite volcano
viii. Caldera
VII. Nature of volcanic eruption
i.…read more

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CS: Lake Nyos
Plate tectonics and associated hazards
In 1912 a German, Alfred Wegener, published his theory that a single continent existed about 300 million years ago. He names
this super ­ continent Pangaea, and maintained that it had later split into the two continents of Laurasia in the north and
Gondwanaland in the south. Today's continents were formed from further splitting of these two masses.…read more

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Sea floor spreading implies that the Earth must be getting bigger. As this is not the case, then plates must be being destroyed
somewhere to accommodate the increase in their size at the mid ocean ridges. Evidence of this was found with the discovery of
huge oceanic trenches where large areas of ocean floor were being pulled downwards.…read more

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Constructive (divergent) margins
Where plates move apart in oceanic areas they produce midoceanic ridges. Where they move apart in continental crust, they
produce rift valleys. Constructive margins are therefore some of the youngest parts of the Earth's surface, where new crust is
continuously being created.
Oceanic ridges
Oceanic ridges are the longest continuous uplifted features on the
surface of the planet, and have a total length off 60,000km. In
some parts they rise 3,000m above the ocean floor.…read more

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The line of the African rift is thought to be an emergent plate boundary, the
beginning of the formation of a new ocean as eastern Africa splits away from the rest of the continent.…read more

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The plates forming continental crust have a much lower density than the underlying layers, so there is not much subduction
where they meet. Instead, as the plates move towards each other, their edges and the sediments between them are forced up
into fold mountains. As there is little subduction, there is no volcanic activity, but the movement of the plates can trigger
shallowfocus earthquakes. Material is also forced downwards to form deep mountain roots.…read more

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Vulcanicity is normally associated with plate margins but, in the centre of the Pacific Ocean, we find the volcanic Hawaiian
Islands that are not connected with any plate boundary. It is believed that this volcanic area is caused by a localised hot spot
within the pacific plate. A concentration of radioactive elements inside the mantle may cause such a hot spot to develop. From
this, a plume of magma rises to eat into the plate above.…read more

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Not at plate boundaries Hot spots: may be neat the Plume volcanoes Hawaiian islands: Emperor
centre of a plate seamount chain
Most volcanic activity is associated with plate tectonic processes and is mainly located along plate margins. Such activity is
therefore found;
Along oceanic ridges where plates are moving apart. The best example is the midAtlantic ridge ­ Iceland represents a
large area formed by volcanic activity
Associated with rift valleys.…read more

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Dykes
Dykes are vertical intrusions with horizontal cooling cracks. They cut across the bedding planes of the rocks into which they
have been intruded. Dykes often occur in groups where they are known as dyke swarms. Many Scottish islands such as Mull
and Skye, have clusters of dykes, all associated with one intrusive event.
Sills
Sills are horizontal intrusions along the lines of bedding planes. Examples include the Great Whin Sill (which carries part of
Hadrian's Wall) and Drumadoon and the Isle of Arran.…read more

Comments

Isobella98

this is soooooo useful, thankyou for sharing :)

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