Factors affecting Volcanic Eruptions

Factors affecting Volcanic Eruptions

1. Dissolved Gases in Magma

   • Dissolved gases such as water vapour and carbon dioxide are present in magma.
     • These gases expand near the surface.
   • Vents = openings near the surface through which molten gases / rock are released.
   • Eruption violence related to how easily gas escapes from magma.
     • Gas escapes easily from less viscous magma.
     • More viscous magma = more explosive eruption.
   • Therefore the more viscous the magma, the more difficult it is for gas to escape the magma, and the more explosive the volcano.

2. Magma Temperature

   • Hotter magma is less viscous = less explosive.
   • Basaltic volcanoes are very hot - 1200°c.
   • Andesitic volcanoes are quite hot - 1000°c.
   • Rhyolitic volcanoes are cooler - 700°c.
   • The cooler the magma, the less viscous the lava, and therefore the more explosive the volcano.

3. Magma Composition

   • Low silica content magma is less viscous = less explosive.
   • Basaltic volcanoes have a low silica content - 42 to 52%.
   • Andesitic volcanoes have a medium silica content - 50% or more.
   • Rhyolitic volcanoes have a high silica content - 70% or more.
   • Therefore the higher the silica content, the more viscous the magma, and the more explosive the volcano.