Distribution of earthquakes and volcanoes
1. Distribution of earthquakes
a) along all plate boundaries
b) largest concentration at the Pacific Ring of Fire
2. Distribution of volcanoes
a) located near convergent and divergent plate boundaries
b) hot spot volcanoes are found away from plate boundaries
3. Distribution of tectonic hazards
a) most located near plate boundaries, and near earthquakes and volcanoes
b) tsunamis and volcanic ash may spread beyond geographic region
The map below highlight the locations of volcanoes, highlighting a concentration of volcanoes around the rim of the Pacific Plate, which is known as the Ring of Fire. This is mainly due to the subduction of the Pacific Plate, which consist of mainly denser oceanic crust below the continental crusts as it converges with the Eurasian Plate, North and South American Plates.
Most of the volcanoes are found at the convergent plate boundaries.
Oceanic-continental plate convergence
• When an oceanic plate meets a continental plate, the denser oceanic plate subducts under the less dense continental plate.
• A subduction zone forms, creating a deep oceanic trench along the plate boundary.
• The subduction of the oceanic plate causes the solid mantle material to melt and magma is formed.
• The magma rises through the mantle and crust to emerge as lava which cools and solidifies to form volcanoes on land such as Mt Merapi in Indonesia.
Oceanic–oceanic plate convergence
When two oceanic plates converge, one subducts under the other.
A subduction zone forms, creating a deep oceanic trench.
The subduction of the oceanic plate causes the solid mantle material to melt and magma is formed.
The magma rises through the mantle and ocean floor to emerge as lava which cools and solidifies to form volcanoes which eventually rise above the sea level to form volcanic islands such as the Mariana Islands.
Revise on how a volcano is formed @
http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/volcanoes_rev1.shtml