Constructive and Destructive Plate Margins
Two plates are moving apart, which allows magma to rise up from the mantle to the earths surafce which creates new crust. Eg mid-alantic ridge. The plate movement at these boundaries causes volcanic eruptions and can also casue earthquakes due to friction of the plates as they move over the mantle. Crust on either side tneds to have cracks/faults in it caused by pressure of moving plates.
Oceanic and continental plate collide, the oceanic plate is denser so it sinks beneath the continental plate (subduction). As it sinks it takes sea water with it which melts to form magma less dense than the mantle. It will rise up through the continental crust and explodes at the surface as a volcano. The trapped sea water turns to steam making the volcano very explosive. There`s not much lava but a lot of steam, ash and gas. As the oceanic sinks beneath the continental it creates friction, which can cause earthquakes. As the continental moves towards the oceanic, the land on the edge of the plate gets crumpled to form Fold Mountains. Eg Andes.
Conservative plate margin and ocean trenches
Conservative Plate Margin
Two plates are moving past each other. The friction between the plates cause earthquakes. They occur close to the earths surface. Eg San Andreas fault
They are a dip found in the crust at destructive plate margins. Mostly under sea.
- Found at destructive plate margins.
- Steep sides
- Alternate layers of ash and lava
- The lava is sticky and doesn`t flow far and is acidic
- Violent eruptions expell steam, ash lava and rock. But are rare.
- Found at constructive plate margins
- Wide base and gently sloped sides
- Runny lava that flows a long way. Its also basic
- Frequent eruptions but not violent
Himalayas Case Study
- Seven climber pay Napalease goverment £50,000 to set set foot on Everest
- Sherpa gets £1600 for 60 days work i fhe reaches the summit
- But tourism is destroying the enviroment. Everest has been described as the highest rubbish dump in the world.
- Providing precious electricity and water for locals is diffucult when there are tens of thousands of tourists to supply for
- The mountian is now becoming very crowded
- 0.5% of their GDP comes from mining. Small scale mining is being encouraged and more mineral surveys are being undertaken to locate the best reserves.
- Nepal has potiental to generate HEP. But only 30% of rural napalease have electricity. There is enough potiental generation to send electricity to India and ths would help Nepal develop.
- 70% of nepal is farming and 35% GDP is from farming.