global distribution of volcanoes

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10 Terms

1
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lithosphere

  • The lithosphere is broken up into a number of rigid large sections called plates

  • There are 7 major plates and several minor plates.

2
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convection currents

  • plates move due to forceful convection currents in the earth’s mantle

  • As a result of plate movements, volcanoes occur.

  • The type of boundary and type of crust involved will determine where the volcanoes will form.

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plate boundary

  • plates meet at a plate boundary.

  • Volcanoes occur at destructive (convergent) and constructive (divergent) plate boundaries.

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divergent plate boundaries

  • occur when two plates pull apart

  • convection currents moving in opposite directions in the mantle cause plates to separate creating a fissure.

  • This fissure or crack allows magma to erupt onto the surface.

  • This process creates volcanic activity - most commonly associated with the formation of shield volcanoes

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seafloor spreading

  • formed when magma cools and solfidifes on the sea bed

  • overtime volcanic mountains or mid ocean ridges occur in these areas

  • with further eruptions these volcanic mountains appear above water and are known as volcanic islands e.g Iceland

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east african rift

  • plates separate on land, east african rift occurs

  • divergent plate boundaries create volcanic activity

  • runs through east of africa where Nubian and Somalian plates are moving away from each other creating rift and rift valleys

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subduction

convergent plate boundaries are where to plates collide and rock is changedd or destroyed

subduction occurs - the older heavier palte, sinks beneath the younger lighter plate

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volcanic acitivty

  • occurs at boundary of two colliding oceanic plates

  • magma from the descending melting plate rises up on the ocean floor and forms islands known as island arcs.

  • These can be active volcanoes e.g Japan - Pacific and Eurasian plates collide

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subduction - oceanic and continental

  • can cause volcanic activity

  • e.g Andes mountains when Nazca plate collides with the South American plate - creating 200 active volcanoes along the Andes range

  • e.g Mount Aconcagua

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transform boundaries

  • e.g San Andreas Fault in California

  • plates slide past each other - no formation or destruction of crust

  • volcanic activty due to release of pressure and movement of magma