Geography Volcanoes

Plate tectonics and the distribution of volcanoes| sample answer
Q: ‘Explain how the study of plate tectonics has helped to understand the global distribution of
volcanoes’ (2008 Q2 B.)
Volcanoes occur where plates of the crust move collide or separate). A fountain or a plume of hot material
can cause a volcano as well. These cause hot material from the mantle to rise to the centre of a plate at a
location called a hotspot.
Molten rocks (magma) from the mantle forces its way through weakness in the crust (faults, plate
boundaries and rifts) towards the surface because of plate tectonics (convection currents).
The earth is covered in a thin, solid crust. The lithosphere is broken into 16 major slabs called plates. Plates
are being constantly moved around by convection currents in the mantle.
As the plates move around the earth, landforms such as volcanos, rift valleys and fold mountains form at the
plate margins and fault lines.
Convergent, transverse and divergent plate boundaries exist where plates move towards each other, slide
past or move away from each other. This movement of plates is called plate tectonics.
Oceanic plates are thinner, only 6-12 km thick, made with dense, heavy rock like basalt. MAde of silicon
and magnesium rich rock as a result they are more dense than continental plates.
Continental plates are 40-60km thick, made with lighter rocks such as granite. Silicon and aluminium rich
rocks make up these plates.
At a constructive plate boundary (where crust is made), magma rises through the gap between the separating
plates and forms volcanic mountains. Mount St. Heleca, Iceland is an example.
The volcanos at constructive plate boundaries are, for the most part found under the ocean, this is because
the majority of constructive plate boundaries are 2 ocean plates pulling apart.
The convection current under 2 plates have to be moving in opposite directions, this causes the plate floating
above to move away from each other.
The...