FORMATIONS

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3 Major Volcanic Zones

Most of these active volcanoes are found in zones near
both convergent and divergent boundaries the lithospheric plates.

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Subduction Zones

Many volcanoes are located along subduction zones,
where one plate moves under another plate.

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Mid-Ocean Ridge

The greatest amount of magma comes to the surface where
plates are moving apart along mid-ocean.

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Hot spots

They are volcanic regions thought to be fed by underlying
mantle that is anomalously hot compared with the mantle elsewhere.

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MAGMA FORMATION

Decompression Melting

• when temperature stays the same but the pressure decreases
• occurs in rift valleys, mid-oceanic ridges, and in volcanic hotspots

Flux Melting

• When volatiles or gaseous substances are added into the hot solid rocks
• Water vapor and CO2 will react with the rocks and weaken or
  break their bonds and cause it to change from solid to liquid state
• occurs in subduction zones

Heat Transfer Melting

• the melting of surrounding rocks caused by very hot magma
  bringing in additional heat
• a very hot magma (1200�C) from the upper mantle could rise and
  cause the melting of rocks in the lower crust
• occurs in rift valleys, mid-oceanic ridges, hotspots,
  and subduction zones

Magma is formed due to:

• Increasing temperature
• Decreasing pressure (pressure-release melting)
• Addition of water