Tectonic Plates and Fold Mountains
3 Types of Plate Margin -
Destructive - Two plates moving towards each other, e.g East coast of Japan. Denser oceanic plate subducts under the less dense continental plate. Landforms - Volanoes, Ocean Trenches.
Constructive - Two plates moving away from each other e.g. the nazca and the south american plates. Magma rises, fills gap and cools, making new crust.
Conservative - Two plates sliding past each other, ether moving in opposite directions or different speeds. No crust is created or destroyed e.g. along the west coast of USA.
Fold Mountains Formation - Destructive plate margins collide causing sedimentary rock to built upwards. They occur at destructive boundries between either oceanc and continental or two continental plates.
Uses of Fold Mountainous Areas -
- Farming - Low Slopes - Growng Crops - High Slopes - Grazing Animals
- Hydro-Electric Power - High lakes store water
- Mining - Major source of metal ores
- Forestry - good environment for growing
- Tourism - Spectacular scenery, sports - e.g. skiing
Formation of Volcanoes - at destructive boundaries
Oceanic plate subducts under the continential plate. Oceanic plate is melted and destroyed, then a pool of magma forms. The magma rises through crack in the crust.The magma erupts onto the surface, forming a volcano.
At constructive boudaries -
Magma rises up into the gap, this gap is created by the plates moving apart. This forms a volcano.
Some volcanoes also form over parts of the mantle that are really hot. These are called hotspots e.g. in hawaii
Three different types of volcanoes -
Composite - e.g. mount fuji in japan - made up of ash and lava that has erupted, cooled and hardened into layers. The lava is usually thick, flows slowly and hardens quickly.
Shield - e.g. Mauna Loa - in the hawaiian islands - made up of only lava which is runny, flows quickly spreads over a wide area, forming a low, flat volcano.
Dome - e.g. mount Pelee in the caribbean - made up of only lava, the lava is thick, flows slowly and hardens quickly to fro a steep sided volcano.
Formation of Supervolcanoes - Formed at destructuve boundries and hotspots e.g. Yellowstone National Park in USA. How they form at hotspots -
- Magma rises through cracks in the crust forming a magma basin below the surface. Pressure of the magma forms a bulge above the surface
- The bulge cracks creating a vent for the lava to escape through
- The lava erupts out of the vents causing earthquakes and sends up gigantic plumes of ash and rock.
- As the basin empties, the bulge is no longer supported and it collapses spewing more lava.
-It leaves behind a huge crater called a caldera which can form a lake.
- Flat, unlike volcanoes which are mountains, cover a much larger area.
- Form a caldera instead of a smaller crater at the top of a normal volcano.
1. Caused by tension that builds up at all 3 different types of plate margins -
Destructive Margins - tension builds when a plate gets stuck during subduction
Constructive Margins - tension builds along cracks within the plates as they move away from eachother
Conservative - tension builds up when plates that are grinding past each other get stuck
2. The plates eventually jerk passed each other, sending out shock waves (vibrations), these vibrations are the earthquakes.
3. The shock waves spread out from the focus - the point in the earth where the earthquake starts. Near the focus the waves are stronger causing more damage.
4. The epicentre is the point on the earth's surface straight above the focus.
5. Weak earthquakes happen quite often but strong earthquakes are rare.
Ways of measuring an earthquake -
- The Richter Scale
- The Mercalli Scale