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Plate Tectonics (plate boundaries (converging (o-o convergence (formation…

- - - - formation of fold mountains
        
        As 2 continental plates move towards each other, they collide and compressional force put rock layers under immense pressure
        
        One plate may be pushed under another but no subduction occurs as both plates are equally light
        
        Their edges and sediments between them start to buckle and fold
        
        immense folding and uplifting of sediments result in the formation of fold mountains
        
        types of folds
        
        isoclinical
        
        chevron
        
        overturned
        
        recumbant
        
        eg. The Himalayas
    - - The denser oceanic plate subducts under the less dense oceanic plate
        
        An oceanic trench, which is a long narrow deep depression, is found at the subduction zone
      - formation of undersea subduction volanoes
        
        The subducted plate melts in the mantle due to heat and produces magma
        
        As magma is less dense than the mantle, it forces its way through fractures and faults to form undersea subduction volcanoes
      - formation of oceanic trench
        
        2 oceanic plates move towards each other
        
        eg. Marianas Trench
      - formation of volcanic island arc
        
        a volcanic island arc is formed when a chain of undersea subduction volcanoes rise over the sea
    - - formation of subduction volcanoes
        
        The subducted oceanic plate melts in the mantle due to heat and produces magma
        
        As magma is less dense than the mantle, it forces its way through fractures and faults to form a subduction volcano on the surface of the continental plate
        
        eg. Mt. St. Helens (USA)
      - formation of fold mountains
        
        Thicker and lighter continental plate overrides the oceanic plate, folds and crumples to form fold mountains
      - formation of oceanic trench
        
        A continental and oceanic plate move toward each other, colliding.
        
        The thinner and denser oceanic plate subducts under the thicker and lighter continental plate
        
        An oceanic trench, which is a long narrow deep depression, is found at the subduction zone
        
        eg Peru-Chile Trench
  - - - formation of mid-oceanic ridge
        
        As 2 oceanic plates move away from each other, fractures are formed at the plate boundary
        
        Magma rises at the zone of divergence, forming a new crust at the plate boundary. (aka sea-floor spreading)
        
        The constant cooling and solidifying of magma on the sea floor forms a mid-oceanic ridge
        
        eg. Mid-Atlantic Ridge
        
        formation of volcanic islands
        
        At various points along the ridge, magma may build to form undersea volcanoes
        
        A volcanic island is formed when these undersea volcanoes rise to the surface of the ocean
    - - formation of rift valleys and block mountains (aka groben and horsts)
        
        Tensile forces from opposite ends of crust pulls rocks away from each other
        2. Tensile forces causes crust to fracture or tear apart, creating normal faults
        
        As crusts on either side of the faults tear apart,the crust in between sinks to form a rift valley
        
        Relative to subsidence, adjacent blocks appear to be uplifted, forming a block mountain
- - - - however some areas are at risk of earthquakes are already built up or are privately owned and this makes it difficult for the govt as they have to spend alot of money to compensate the land owners
      - refers to a set of rules which are implemented to restrict development in certain areas such as low-lying areas that are vulnerable to tsunamis.
      - eg. maps detailing places at risk of liquefaction are charted in California and new building developments are restricted across fault lines
    - - reduces casualties and economic damages as buildings will not collapse and pose risks of injury or death, and buildings do not have to be rebuilt
      - infrastructures such as home and office buildings should also be fitted with trip switches to ensure all electrical points are switched off to prevent electrical fires in the event of an earthquake
      - these earthquake resistant features are expensive and many countries would rather demolish existing buildings than spend money to add these features
      - earthquake resistant features such as using steel and reinforced concrete and damping devices allows buildings to be able to withstand the shocks from earthquakes, preventing them from collapsing
      - eg. Taipei 101 is made of steel, reinforced concrete and a damping device is added to act as a conterweight which moves in the direction opposite to the motion of the earthequake
    - - Since emergency drills are designed with the most serious earthquake recorded in the area in the past, it can be inadequate if the earthquake occurs at an unprecedented rate
      - people may become complacent and not take the drills seriously, reducing the effectiveness of this strategy
      - people in earthquake prone areas listen to instructions given by trained personnel to move to safe locations and also practice their first aid skills to prepare for an event of injuries inflicted by an earthquake
      - eg. Japan practices emergency drill every 1st Sept where an earthquake of high magnitude is simulated. This has been effective as people are mentally prepared and know how to react in the event of an earthquake
    - - warning systems are usually activated seconds before the earthquake strikes, not giving people much time to react and evacuate the affected areas
      - eg. Tokyo issued out warnings through mobile phones when seimometers detected an earthquake off the coast of Tohoku in 2011, giving people in Tokyo 1min to brace for the impact of the earthquake
      - using technology such as earthquake sensors and seismometers can hep detect possible developments of an earthquake. once seismometers detect seismic waves, it sends out a public warning to advise people to evacuate to safer areas
      - the Pacific Warning Centre in Hawaii also issues out warnings to Pacific nations when a potential tsunami is recorded