Plate techonh

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The structure of Earth- 4 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 5500°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 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

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Convection Currents

within the mantle determine the direction of plate movement. The Earth's crust is broken up into pieces called plates. Heat rising and falling inside the mantle creates

 

 

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Plate Key Words

 

Plate tectonics cause earthquakes and volcanoes.

Plate boundary The point where two plates meet 

Plate boundaries Earthquakes and volcanoes are most likely to occur either on or near .

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Contrasts between oceanic and continental crust

Oceanic:

Continental:

Older,Over 1500 million years old ,Less dense,Cannot sink ,Cannot be renewed or destroyed

(http://floralpower.com/images/Fig21oceancont.gif)

 

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Fold Mountains and Ocean Trenches

Young fold mountains (those formed in the last 65 million years) are the highest areas in the world. Young fold mountains include ranges such as the Himalayas, Rockies, Andes and Alps. Ocean Trenches form some of the deepest parts of the ocean.

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Types of plate margin- DESTRUCTIVE

Convection currents in the mantle causes the plates to move together.

One plate is made from oceanic crust and the other continental crust.

The denser plate (Oceanic) sinks under the lighter (Continental) crust (known as Subduction)

Great pressure occurs and the oceanic crust is destroyed as it melts to form magma.

A good example of a destructive plate boundary is where the

Nazca plate dives underneath the South American plate.

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Types of plate margin-CONSTRUCTIVE

Convection currents also cause plates to move apart, as the plates pull away from each other, cracks and fractures form between the plates where there is no solid crust.

Magma forces its way into the cracks and makes its way to the surface to form volcanoes. In this way new land is formed as the plates gradually pull apart.

They cause mid ocean ridges to form, an example of this is the mid Atlantic ridge, a constructive plate through Iceland, where the North American plate and the Eurasion plate are moving away from each other.

Volcanoes can also form here, along the edges of the plate boundary, due to the rising magma. These volcanoes are called

shield volcanoes. 

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Types of plate margin-CONSERVATIVE

At Conservative plate boundaries, the plates are sliding past each other. They are moving in a similar (though not the same) direction.

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. At a conservative plate crust is being neither destroyed nor made.

The best-known example of a conservative plate boundary is the San Andreas Fault, where the North American and Pacific plates are actually moving in the same direction, but at a different speed

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Types of plate margin-COLLISION

At a collision margin two continental crusts collide neither can sink. Instead they push into each other forcing material to be folded up into huge mountain ranges. Often this movement and pressure can cause earthquakes, but no volcanoes will occur on these boundaries.

The best example is found where the Indian plate collided with the Eurasian plate to form the Himalayas

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What landforms occur at each plate boundary?

Conservative- Earthquakes

Constructive-Earthquakes and shield volcanoes

Destructive- Earthquakes, composite volcanoes,ocean trench and Fold mountains

Collision- Fold mountains

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Fold Mountains-Formation

 

Form along both

destructive and collision plate boundaries (where two plates are pushing towards each other)

The best examples are the Himalayas, the Rockies, the Andes and the Alps, all of which are huge fold mountain ranges caused by the collision of two plates.

The general theory is that as two plates, with land masses on them, move towards each other they push layers of accumulated sediment in the sea between them up into folds. Thus most fold mountains will continue to grow, as the plates constantly move towards each other.

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Fold Mountains-Uses

  • Farming
  • Tourism
  • Mining
  • Hydro-electric power
  • Forestry
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Fold Mountains-Problems

Mountainous regions are particularly difficult to build in due to the steep sided valleys and cold climate. Roads and other communications links have to snake their way up wherever they can, and often these roads are not big enough to adequately service a large community.

The climate is very cold and wet, meaning that most industrial and agricultural activity is difficult. For farmers they have a very short growing season, and it is difficult to use machinery on the steep slopes. Avalanches are a constant threat, as was seen to devastating effect in Ranrahirca, Peru, in 1962. Huge amounts of money are spent each year to try and combat the avalanche threat, especially with the large amount of tourists using the

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Volcano-Formation

Volcanoes form where magma escapes through a vent, which is a crack in the earth's surface. This often happens at plate boundaries such as at destructive and constructive plate boundaries. They are also formed at

Hot spots such as those found in Hawaii.

As two plates move towards each other, the heavier oceanic plate is forced under the lighter continental plate at the subduction zone. Here the oceanic plate melts due to the friction/pressure and forms lava which is significantly different to the mantle. This rises through cracks in the rocks where it eventually erupts at the surface, to form a

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Key Terms

 

 

 

 

Pyroclastic Flows

- A cloud of red hot gas and ash which flows down the side of a volcano at 200km/hr

Lahars

- A mixture of ash with rain or glacier melt water which forms a deadly river of mud

Lava Flow

- A river of molten rock 1000 degrees centigrade that can travel at 40mph

Volcanic bombs

- Rocks and lava the size of houses and cars can be hurled into the sky

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Shield Volcanoes

 

Example: Mount Kilauea in Hawaii (USA), Galapagos Islands, Snake River Plain in Idaho, USA.

When lava is runny and thin it can flow a long way before cooling and solidifying, this causes shield volcanoes to have gentle slopes and wide bases built almost entirely of low viscosity basaltic lava flows. Shield volcanoes are the largest of the three types. The eruptions are generally non explosive due to the low silica content and may last for years.

 

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Composite Volcanoes

 

Example: Mount St Helens in Alaska (USA), Mount Shasta in California, Mount Rainier in Washington state, and Mount Fuji in Japan.

Composite volcanoes are the most deadly of volcano types. They are made of alternate layers of ash and lava and have steep sides built up by eruptions of intermediate viscosity andesitic lava and explosive tephra. Often the lava cools creating a plug which blocks the vent resulting in a huge explosion blowing out the plug

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Monitoring and predicting volcanoes.

 

Mt St Helens was predicated and prepared for, but the exact date and time of eruption took people by surprise. Earthquakes are a frequent sign of an impending eruption and their frequency and strength can be recorded. Gases being emitted from the vent change before an eruption and there is an increasing amount of sulphur dioxide. Today robots called ‘spiders’ are often used to monitor changes. The past frequency of eruptions, the gap between them, pattern of lava flows, and ash movement can tell us about how a volcano is likely to behave,

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Supervolcanoes

 

Supervolcanoes are on a much bigger scale than volcanoes. They emit at least 1,000km3 of material – compare this with an eruption on the magnitude of Mt St Helens which emitted some 1km3. Supervolcanoes do not look like a volcano with its characteristic cones. Instead, they are large depressions called calderas, often marked with a rim of higher land around the edges.

Yellow stone is a example of a supervolcano

 

 

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Earthquakes-what is a earthquake and how are they

 

Earthquakes are vibrations in the earth's crust They occur along all plate boundaries but are more destructive usually at destructive plate boundaries. The place where earthquakes begin deep within the earths crust is called the

focus. The point above the focus where the earthquake is most strongly felt is called the epicentre.

 

 

The magnitude or size of an earthquake can be measured by an instrument called a

seismometer and are shown on a seismograph. The earthquakes strength is measured on the Richter scale from a value of 1 to 10. Each level of magnitude is 10 times more powerful than the previous. Therefore a level 7 is 100 time more powerful than a level 5.

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why do earthquakes occur?

At destructive plate margins, the pressure resulting from the sinking of the subducting plate and its subsequent melting can trigger strong earthquakes as this pressure is released.

At constructive plates, earthquakes tend to be less severe than those at destructive or conservative plates. The friction and pressure caused by the plates moving apart is less intense.

Earthquakes tend to be of greater strength at conservative plates. Here where th plates slide past each other the plates tend to stick for a period of time. This causes stresses and pressure to build up. The release of this pressure occurs in a sudden, quick release of the plates and the result is an earthquake.

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Factors affecting the impact of an earthquake

Distance from the epicentre the effects of an earthquake are more severe at its centre.

The higher on the Richter scale, the more severe the earthquake is. Level of development (MEDC or LEDC ) – MEDCs are more likely to have the resources and technology for monitoring, prediction and response.

Population density (rural or urban area). The more densely populated an area, the more likely there are to be deaths and casualties.

Communication - accessibility for rescue teams.

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