Geography - Tectonics

What happens at a Constructive plate margin?

• The 2 plates are moving apart

• This causes magma to rise up from the mantle and form new oceanic crust

• This normally happens under oceans

• It forms underwater volcanoes (some are so large you can see them above sea level such as Iceland)

What happens at a Destructive plate margin?

• The 2 plates are moving towards eachother

• The oceanic plate is being pushed under the continental plate as it is denser

• This forms a deep sea trench

• Oceanic crust is melted into magma by the mantle and rises along the fault lines to form volcanoes

What happens at Conservative plate margins?

• The 2 plates are sliding past eachother

• When the plates stick it causes tension to build up

• When this tension is released an earthquake occurs

• The crust is neither created nor destroyed

• Volcanic eruptions DO NOT occur

• (San Andreas fault line in Los Angeles)

What happens at Collision plate margins?

• The 2 plates are moving towards eachother BUT are both continental plates

• Neither plate can be subducted so the crust is crumpled upwards to form Fold Mountains (Himalayas)

What are Infra-plate Earthquakes?

Earthquakes in the middle of plates on fault zones where the tectonic plate is being squashed, forcing the pressure to be released through the cracks.

Energy travels up cracks in the plate and causes an earthquake

(They’re usually weaker, lower energy but they’re shallow focus)

What are Infra-plate Volcanoes?

A hotspot is a plume of super-heated magma in the mantle.

As the plate moves over the hotspot, volcanoes and new crust are created. The plate moves, but the hotspots remain stationary.