Volcanoes and Earthquakes


Volcanoes are points at the Earth’s surface where molten rock (magma) breaks through the Earth’s crust and flows out onto the surface.  When the magma reaches the surface it is classed as lava.  They often occur at destructive plate margins but can also be found at constructive plate margins or away from plate margins at hotspots.

Structure of a volcano courtesy of Wikipedia. 1. Large magma chamber 2. Bedrock 3. Conduit (pipe) 4. Base 5. Sill 6. Dike 7. Layers of ash emitted by the volcano 8. Flank 9. Layers of lava emitted by the volcano 10. Throat 11. Parasitic cone 12. Lava flow 13. Vent 14. Crater 15. Ash cloud

The Formation of Volcanoes

Volcanoes are formed when magma is forced up to the surface through cracks in the crust.  At a destructive plate margin, the rubbing of the 2 plates creates friction which in turn heats and melts the rock creating magma.  As the quantity of magma trapped within pockets in the crust increase, so too does the pressure.  Eventually the pressure will become so great that the magma will force its way along the path of least resistance, through cracks in the crust, to the surface.  As pressure continues to build within the newly formed magma chamber, it will reach a point when the pressure is so high it is released via the main vent.  Eruptions occur in different ways at different volcanoes as detailed below.

Volcanoes are categorised into 3 types:

Shield Volcanoes

Image courtesy of Wikipedia

Composite Volcanoes

Image courtesy of US Geological Survey

Cinder Cone Volcanoes

Image courtesy of US Geological Survey


Effects of Volcanoes