3.1.5.2 Plate Tectonics 2 Flashcards
3 types of plate margins
Destructive (convergent)
Constructive (divergent)
Conservative
What are the 3 types of destructive (convergent) plate margins
Oceanic + continental -> subduction
Oceanic + oceanic -> subduction
Continental + continental -> collision
What happens at a destructive margin
2 plates collide (converge)
Describe what happens when oceanic plate meets continental plate (subduction)
- Oceanic plate is denser + subducts under continental plate
- continental plate is lighter + less dense
- friction + melting occurs between 100km+700km deep where oceanic plate is melted -> Magma is formed and rises as it’s less dense than crust
What’s the zone called where friction + melting occurs in subduction
Benioff zone
2 landforms created when oceanic meets continental (destructive)
Ocean trenches - oceanic plate bends
Fold mountains - continental land mass uplifted,compressed + folded
2 hazards when oceanic meets continental (destructive)
- intermediate + deep focus earthquakes
- explosive volcanoes
Why do earthquakes occur
Due to the tension being released
Describe what happens when 2 oceanic plates meet (destructive subduction)
When they collide, 1 plate (faster/denser) subducts beneath the other, there is melting in the Benioff zone and magma rises
2 landforms formed when 2 oceanic plates meet (destructive subduction)
- ocean trenches
- island arcs
2 hazards when 2 oceanic plates meet (destructive subduction)
- deep focus earthquakes
- explosive acid volcanoes
Describe what happens when 2 continental plates meet (destructive collision)
Colliding plates + anything deposited between then get u-lifted + buckle (high fold mountains) - both plates are buoyant
2 landforms formed when 2 continental plates meet (destructive collision)
- fold mountains
- Nappe
Example or fold mountains
The Himalayas
What’s nappe
A large body/sheet of rock moved about 2km
What’s the main hazard created from 2 continental plates meeting (destructive collision)
Shallow focus earthquakes -> tension from crust being strained
What happens at constructive (divergent) plate margins
2 plates separate
What divergence happens in oceanic areas
Sea-floor spreading on either side of mid-oceanic ridge e.g mid-Atlantic ridge
What divergence happens in continental areas
Stretching + collapsing of crust forming rift valleys e.g Great African Rift Valley
What plate margins would you find some of the youngest rocks on earth
Why
Constructive (divergent)
As new crust is being formed as the gap created by spreading plates is filled by magma rising from the asthenosphere
As the magma cools, it solidifies to form new,dense basaltic rock
Describe what happens at conservative plate margins
What hazard occurs
E.g of conservative plate margin
2 plates slide past each other in opposite directions/at different speeds
As this happens, stress builds as the plates snag + grind on each other, causing earthquakes
E.g Haiti, San Andreas fault
