Geography- Physical

Constructive eg, Mid Atlantic Ridge (10,000km)

• Plates are pulled apart by convection currents 
• Reduction in pressure leads to the mantle melting and forming magma
• Thinning crust may bow upwards due to pressure below & low density
• Magma produces submarine volcanoes
• Transform faults are produced at right angle to the ridge system

Low level explosivity eruptions and NO SUBDUCTION

Conservative eg, San Andreas fault

• Pressure comes from the friction that is made from the plates sliding past each other. 

No volcanoes, no new landoforms as there is no melting of a subducted plate

San Andreas- Pacific plate moving NW/ American plate moving SE 

Hot Spot eg, Hawaii

Plumes of magma are rising from the asthenosphere, eventhough they are not necessarily near a plate boundary.

• If the crust is thin/weak the magma may escape as a volcanic eruption.
• Lava is basaltic and free-flowing.
• Earthquakes- smooth and regular.

Continental-Continental eg, Himalayas

• 2 plates collide with each other and are forced upwards creating fold mountains. 
• No volcanoes as no magma is rising towards the surface.

Himalayas- Indo-australian plate is moving north(5cm per year)/Eurasian plate is moving south and they collide.

Oceanic-Continental eg, Peru-chile trench

• Oceanic plates slides beneath the continental plate and melts at the subduction zone.
• Volcanoes are explosive as there is more pressure due to there being more plate to get through.

Peru-chile trench- Nazca plate subducts the SA plate. Andes are formed (fold).

Oceanic-Oceanic eg, Japan Trench

• Older of the 2 oceanic plates subducts and erupt immediately with 50% silica content.
• Island arc is formed (magma breaks through).

Japan Trench(Marina islands)- Pacific plate subducts the Philippine plate.