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Plate Tectonics
The structure of the earth

The earth structure is split up into four layers, these are the crust , mantle, outer core and
inner core.

The crust: The crust covers the mantle and is the earth's hard outer shell, the surface on
which we are living. Compared to…

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Both parts are in a series of interlocked pieces called plates
The point between 2 plates is called a plate boundary
The plates are constantly moving (very slowly). In parts of the world where the plates are
moving apart, a constructive (or divergentl) plate boundary is formed. New oceanic crust…

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began to split and 50 million years ago they had started to spread out into the world map we know
today.

Evidence to support this includes:

Fossil evidence - same species of land animals found on opposite sides of the Atlantic Ocean
Climate evidence - coal deposits and fern fossils…

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Typical slopes of 15°
Lava flows down slope, away from the central vent
Many shield volcanoes have a central caldera
Examples: Hekla and Katla

Ocean Ridge Volcanoes

Volcanic activity under water, for example at the Mid Atlantic Ridge
Submarine oceanic ridge volcanoes e.g. Surtsey 1964, form new islands
Passive volcanic…

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Destructive Plate Boundaries
These types of boundaries are:

Continental-Continental Boundaries
Oceanic-Oceanic Boundaries
Oceanic-Continental Boundaries

Continental-continental Boundaries

When two continents meet in a collision
zone, there is very little/no subduction (no
volcanic activity as neither are absorbed into
the mantle) as both are relatively light and
buoyant, resisting downward movement. The…

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towering heights which they attain as they approach the coast
Waves travel at 800kilometres an hour , but due to enormous wavelength the wave
oscillation can take 20-30mins to complete a cycle and has amplitude of 1metre.
Very difficult to detect over deep water meaning they go unnoticed by ships…

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The magma is very gaseous, particularly when enriched with water vapour - high explosive
eruptions
Stratovolcanoes are constructed from feeder conduits extending to the surface
Granitic (rhyolitic) intrusions are also formed, becoming trapped within the volcanic pile
overlying the region of subduction giving potential for very explosive eruptions

Stratovolcano/ composite…

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The rising mantle material is called a mantle plume.

Very passive eruptions from shield volcanoes due to the magma's composition

Case Study: Hawaii

Long chain of 129 volcanoes, of which 123 are now extinct as the plate moves north-west

As the plate continues to move there will be a new…

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movement generates shock, or seismic waves which travel outward from the point where
the energy was released, known as the focus.
Most damage will occur at the epicentre, the point on the earth's surface immediately above
the focus.

P and S Waves

P waves: primary waves: these are longitudinal waves…

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Risk Assessment involves not only hazards from a scientific point of view but also the socio-economic
impacts. Risk is a statement of probability that an event will cause a certain amount of damage or a
statement of economic damage of an event. It consists of:

Hazard assessment as above
Looking…

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