What happens where an oceanic plate meets a continental plate?

The denser oceanic plate is forced down beneath the continental plate into the mantle, producing a deep ocean trench offshore and fold mountains with volcanoes inland.

Explain why magma is generated above a subducting slab.

Water held in the wet sediments and minerals of the descending plate is driven off as the slab heats, and it lowers the melting point of the mantle wedge above so that the mantle melts.

Why is magma at a subduction zone so explosive?

It rises through and melts silica-rich continental crust, becoming viscous andesitic magma that traps its dissolved gas until the pressure is released violently.

What is the Benioff zone?

The Benioff zone is the inclined band of earthquake foci that marks the descending slab at a subduction zone, dipping away from the trench beneath the overriding plate.

WJEC A-Level Geography 601-8455-3

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Tectonic Hazards

Convergent margins and subduction

3 things to know
AS Unit 1 and A2 Unit 4

Overview

Three kinds of convergent plate margin, why magma is generated above a subducting slab and benioff zone.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What are the three kinds of convergent plate margin?

Key term

Name a mountain range formed at an oceanic to continental margin and the plates responsible.

Key term

To what depth do earthquakes occur within a Benioff zone?

Questions from this subtopic

Each one with the model answer underneath.

1
What are the three kinds of convergent plate margin?
Model answer
Oceanic plate meeting continental plate, oceanic meeting oceanic, and continental meeting continental.
2
What happens where an oceanic plate meets a continental plate?
Model answer
The denser oceanic plate is forced down beneath the continental plate into the mantle, producing a deep ocean trench offshore and fold mountains with volcanoes inland.
3
Name a mountain range formed at an oceanic to continental margin and the plates responsible.
Model answer
The Andes, formed as the Nazca plate is subducted beneath the South American plate.
4
Explain why magma is generated above a subducting slab.
Model answer
Water held in the wet sediments and minerals of the descending plate is driven off as the slab heats, and it lowers the melting point of the mantle wedge above so that the mantle melts.
5
Why is magma at a subduction zone so explosive?
Model answer
It rises through and melts silica-rich continental crust, becoming viscous andesitic magma that traps its dissolved gas until the pressure is released violently.
6
What is the Benioff zone?
Model answer
The Benioff zone is the inclined band of earthquake foci that marks the descending slab at a subduction zone, dipping away from the trench beneath the overriding plate.

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