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Volcanic Environments
Learning goal
• To understand the natural processes affecting
the distribution of volcanic environments
Continental crust
• Plates consist of either continental crust or
oceanic crust
• The continental crust is older, thicker (35 to 75
kilometres), lighter (mainly granite) and
cannot sink
• Continental crust extends beyond the present
coastline to the edge of the continental shelf
of each continental mass
Oceanic crust
• The oceanic crust is younger, thinner (less
than 10km) heavier (mainly basalt), can sink
(be subducted) into the mantle and is
constantly being destroyed and replaced.
• These differences account for the variations in
the level of both volcanic and earthquake
activity at plate boundaries, and the variations
in landforms
Cheesy Rap
• http://www.youtube.com/watch?v=dkELENdZ
ukI
Type of volcanic activity
• The level and type of volcanic activity are determined by
the direction of the plate movement and whether the
plates are oceanic or continental
• The oceanic plates consist mainly of basalt, which
originates from the rising magma in the upper part of the
mantle, beneath the ocean ridges as the plates pull apart
• Where the oceanic plate is subducted under the
continental plate, the molten material, magma, consists of
3 different materials: some from the upper mantle directly
above the descending oceanic plate, some from the partial
melting of the oceanic plate itself and some from the lower
part of the continental shelf
• This results in the volcanic rocks formed under continental
plates being far more complex than the volcanic rocks
formed under oceanic plates.