The Restless Earth

fold mountains
1. when tectonic plates collide, the sedimentary rocks that have built up between them are folded/forced upwards to form mountains. these are formed at destructive plate margins.
  1. example: Himalayas, indian and eurasian plates BOTH continental, neither subducted due to density caused upwards fold
2. fold mountains used to: graze cattle, terraces constructed to grow crops, hydroelectric power scource from high lakes, forestery, mining for metal ores, tourism.
tectonic plates
1. the structure of the earth: inner core (iron and nickel), outer core (iron and nickel), mantel (magma) and the crust.
  1. oceanic crust - thicker and covers the ocean basins. continental crust - lesser in density, covers 40% of the earth and made of granite
2. the earths crust is formed by plates. heat rising and falling in the mantle creates convection currents, these currents cause the plates to move
  1. volcanoes are usually located on or near plate boundaries, most commonly destructive and constructive.
    1. destructive plate boundaries - oceanic and continental plates move together, oceanic plate is forced under the lighter continental plate, friction causes melting of oceanic crust which causes earthwqaukes and also magma rises up to the surface through cracks.
      1. example of this - Nazca plate forced under South American plate.
    2. constructive plate boundaries - when plates move apart from each other, volcanoes form as the magma rises up to fill the gap created.
      1. an example of this is the Mid Atlantic Ridge.
    3. conservative plate boundaries - when plates slide past each other in opposite or the same directions but at different speeds. but eventually friction is overcome and causes sudden movement causing shock waves which produce earthquakes. VOLCANIC ERUPTIONS CAN NOT TAKE PLACE AT THESE MARGINS
      1. example of this is the San Andreas fault.
volcanoes and volcanic eruptions
1. formation of volcanoes : 1 - magma rises through cracks or weaknesses in crust . 2 - pressure builds up inside. 3 - pressure is released due to plate movement and magama xplodes to the surface causeing an eruption. 4 - the lava from the eruption cools to form the new crust. 5 - after several eruptions the rock builds up and a volcano forms.
2. types of volcano: shield volcanoes - usually found at constructive boundaries, low with gently sloping sides, eruptions tend to be frequent yet relatively gentle. composite volcanoes - made of layers of lava and ash, found at destructive boundaries, eruptions usually pyroclastic flow.
  1. supervolcanoes - a volcano on a massive scale. forms a depression (caldera), has a ridge of higher land around it, eruptions are hundreds of thousands of years apart. results of an eruption are devastating, 1,000 km3 of material.
    1. Yellowstone (supervolcano) - last eruption occured 630,000 years ago and was 1,000 times bigger than the Mount St Helens eruption. the large volume of material from the last eruption caused the ground to collapse creating a caldera ( 55km by 80km wide). the next eruption is predicted to have worldwide effects.
earthquakes
1. earthquake - shaking and vibration of the earths crust due to movement of the earths plates. they can occur at any type of plate boundary.
2. when plates move next to eachother and get stuck, pressure builds up and when it is released an earthquake tends to occur.
  1. the point in the crust where the pressure is released is called the focus, the point on the earths surface is called the epicentre.
3. the power of an earthquake is measured using seismometer which detects vibrations. the strength (magnitude) of an earthquake is measured using the richter scale numbered 0-10, the higher the number the higher the magnitude.
  1. Mercalli scale measures the intensity of an earthquake by analysing the effects and damage caused by it.
4. effects of an earthquake (short-term) : people killed or injured, homes destroyed, shops and businesses destroyed, lootings, damage to transport and communications, fires can spread due to gas pipes, damaged wood areas, tsunamis and landslides may occur
5. effects of an earthquake (long-term): disease may spread, rehousing and refuge camps, high cost of rebuilding settlements is high, important natural and human landmarks can be lost/

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Inside A Volcano (image/gif)

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The Restless Earth

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