Hazardous earth
- Created by: Austen Poole
- Created on: 09-03-17 09:57
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- Hazardous Earth
- Basic structure of the earth
- The mantle-crust boundary
- Marked by the mohorovicic discontinuity / moho
- Depth below continents = 35km
- Depth below oceans = 10-15km
- Properties
- Crust
- Continental
- Mainly Granitic, silicon, aluminium
- Density = 2.6-2.7 km/m cubed
- Thickness: mean: 35km, min: 30km, max: 70km
- Oceanic
- Mainly Basaltic, silicon and magnesium
- Density = 3.0 km/m cubed
- Thickness = 5-10km
- Continental
- Mantle
- Rich in magnesium and iron
- Crust
- Marked by the mohorovicic discontinuity / moho
- Upper Mantle
- Asthenosphere
- Extends from 100km down to 300km down
- Semi-molten, viscous, capable of flowing slowly
- Lithosphere
- Above the Asthenosphere
- Rigid layer sandwiched between the crust and the Asthenosphere
- Varies in thickness
- Undefined boundary as it melts
- Asthenosphere
- The mantle-crust boundary
- Continental drift
- Alfred Wegner
- He believed that there was one large continent and it split into many and they drifted apart
- The large single continent was called Pangea
- Although scientist believed wegners theory they did not know how the continents moved
- This left scientists sceptical about the theory
- paleomagnetism
- This showed that new land was being formed under the ocean by underwater volcanoes
- This was linked with Wegners theory in the 1960's
- Alfred Wegner
- Plate boundaries
- Divergent (constructive)
- This is where the plates are moving apart and magma is reaching the surface
- They are mostly found at mid-ocean ridges
- These consist of very long chains of mountains
- The lava formed here is pillow lava because it cools almost as soon as it touches the water
- The chains are not continuous
- They are broken up by transform faults that displace the ridge sideways
- Transform faults do not have any volcanic activity, but they release energy as earthquakes when they move
- They are broken up by transform faults that displace the ridge sideways
- The largest extrusion of magma at one of these plate boundaries has formed Iceland
- Black smokers - these are found at these plate boundaries
- When water flows into rifts it is super heated. The water then rises causing changes in the rocks.
- This causes metal sulphide to mix with the water turning it black.
- These support unique and highly specialised organisms and ecosystems
- When water flows into rifts it is super heated. The water then rises causing changes in the rocks.
- Rifting is not confined to the ocean floor
- They can also occur on land e.g. the rift valley
- Convergent (destructive)
- Plates may converge in 3 different ways
- oceanic - continental
- Subduction occurs here
- An ocean trench is formed by the subduction
- Fold mountains are formed by the movement of the oceanic crust under the continental crust
- The angle of subduction is between 30 and 70 degrees
- Faulting and fracturing occur in the benioff zone
- As the subducted plate melts the magma rises pushing fold mountains upwards
- Fold mountains are formed by the movement of the oceanic crust under the continental crust
- When the magma reaches the surface it forms volcanoes
- oceanic - oceanic
- the slightly denser plate will subduct under the other one creating a trench
- Island arcs are formed when the magma reaches the surface
- continental - continental
- Little, if any subduction takes place
- fold mountains form e.g. The Alps
- oceanic - continental
- Plates may converge in 3 different ways
- Conservative
- These plate boundaries slide past each other
- Earthquakes are caused by the build up of pressure
- The plate boundary is sometimes visible as they look like a large tear through the landscape e.g. the san andreas fault
- Divergent (constructive)
- Basic structure of the earth
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