TECTONICS

TECTONICS

1. TECTONIC PLATES

   • The Earth's crust is made up of seven principal tectonic plates
   • Oceanic crust is often only about 5km thick, but is very dense
   • Continental crust is thicker, often being approximately 30km deep, but is less dense.
   • Tectonic Plates all move very slowly on the mantle
     • meeting along the four main boundaries that can be found in the next section
   • the plates move due to convection currents in the mantle
     • hot currents of molten rock

2. PLATE BOUNDARIES

   • Destructive plate boundaries
     • cause violent volcanoes and earthquakes, as well as deep-ocean trenches and fold mountains.
     • An oceanic plate and continental plate move towards each other
     • denser oceanic plate dives under the lighter continental one, creating a deep ocean trench.
     • As the oceanic plate goes deeper into mantle it melts in the subduction zone, due to friction and the increased temperature.
     • newly molten rock is lighter that that which surrounds it, so it will rise towards the surface and cause volcanoes on the earth's surface.
     • The continental crust is crumpled by the collision of the two plates creating Fold Mountains.
     • If the magma rises offshore it will form an Island Arc
   • Constructive Plate boundaries
     • occur on constructive plate boundaries
     • cause mid-ocean ridges to form.
     • Two plates move away from each other
     • Molten rock rises from the mantle to fill the gap between the two plates
     • Volcanoes can also form here, along the edges of the plate boundary called shield volcanoes.
   • Conservative plate boundaries
     • The main effects of a conservative plate boundary are earthquakes
     • Two plates slide past each other
     • As they move past each other they often get stuck
   • Collision Margins
     • two continental crusts collide neither can sink
     • push into each other forcing material to be folded up into huge mountain ranges.
     • movement and pressure can cause earthquakes, but no volcanoes will occur on these boundaries.

3. VOLCANOES

   • Mt. St. Helen's, May 1980 (The U.S.A.)
   • destructive and constructive boundaries
   • Acid cone volcanoes are steep sided due to the fact that the lava is thick and acidic
   • Shield cone volcanoes are wide-based, with gentle slopes
   • Composite Cone volcanoes are steep-sided,and made of alternate layers of ash and lava.

4. EARTHQUAKES

   • occur along faults, which are large cracks in the earth's crust.
   • caused by the sudden jerking movements
   • Richter scale measures the magnitude of an earthquake using an instrument called a seismograph.
   • mercalli scale measures the damage caused by an earthquake
   • primary effects - buildings road collapses etc
   • secondary - tidal waves land slides diseases fires
   • KOBEJAPAN

5. FOLD MOUNTAINS

   • Form along both destructive and collision plate boundaries
     • where two plates are pushing towards each other.
   • at a destructive plate boundary the oceanic plate is subducted beneath the continental one.
   • formation at collision margins - both plates are Continental ones, and so can neither sink nor be destroyed. The material between them is therefore forced upwards to form the mountains.
   • Farming is a primary activity in all of the fold mountain ranges
   • Tourism is another major use of the Fold Mountains
   • Forestry is another big business in these mountainous regions
   • generation of hydroelectric power (HEP)
   • Mountainous regions are particularly difficult to build in
   • Avalanches are a constant threat,
   • climate is very cold and wet

6. IMPACT

   • MEDC's have the medical resources and money to quickly get appropriate aid to areas after a natural disaster
   • In MEDC's who have a volcanic or earthquake risk, such as Japan and New Zealand,there are well thought out emergency procedures
   • developing buildings that have more chance of resisting an earthquake
   • Scientists work throughout the world, trying to predict earthquakes and volcanoes
   • MEDC's tend to be able to recover quickly from a natural disaster