Coastal and Oceanic Landform ( 52. Volcanic Arc )

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  •  A volcanic arc is a chain of volcanoes.
  • Positioned in an arc shape.
  • Offshore volcanoes resulting in a volcanic island arc.
  • They result;

                      -Subduction of an oceanic tectonic plate under another tectonic plate.
                     -Often parallel an oceanic trench.

  • The oceanic plate is saturated with water.
  • It volatiles water drastically lower the melting point of the mantle.
  • Pressure squeezes water out of the plate.
  • It comes to the mantle.
  • After melting mantle ,forms magma at depth under the over riding plate.
  • The magma ascends to form an arc of volcanoes parallel to the subduction zone.

  • The Hawaiian Islands hotspot chain,

                                        The older islands (tens of millions of years)
                                        Which is more rocky.
  • Volcanic arcs do not generally exhibit simple age pattern.
  • There are two types of volcanic arcs:

1.Oceanic Arcs 

  • Formed oceanic crust.
  • Subducts beneath other oceanic crust.
  • On an adjacent plate.
  • Creating a volcanic island arc.
  • Not all island arcs are volcanic island arcs.
e.g.Mariana Islands ,western Pacific Ocean
      Lesser Antilles,western Atlantic Ocean.
     Cascade Volcanic Arc,western North America
     Andes,western edge of South America

2.Continental Arcs

  • Form oceanic crust.
  • Subducts beneath continental crust.
  • On an adjacent plate.
  • Creating an arc-shaped mountain belt.
  • Not all mountain belts are formed this way.

  • Cascade Volcanic Arc
  • Alaska Peninsula 
  • Aleutian Range
  • Kamchatka
  • AndesNorth Volcanic Zone
  • Central Volcanic Zone
  • South Volcanic Zone
  • Austral Volcanic Zone
  • Central America Volcanic Arc

  • There are isolated.
  • Most volcanoes in a mountain belt.
  • Vesuvius & Etna , Italy part of separate.
  • Different kinds of mountainous volcanic ensembles.

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