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Definition of volcano:
- A mountain formed of lava and pyroclastics
- Factors affecting magma formation
Where do volcanoes form?
• Seduction boundaries
• Divergent boundaries
• Over hot spots
o Unusually hot regions of earth’s mantle where mantle material rises to the surface
o A trail of progressively older volcanoes forms as a plate moves over a hot spot
Factors affecting volcanic eruptions:
• Magma composition
• Temperature
• Amount of dissolved gases
o Magma composition and temperature affect the magma’s viscosity-resistance to flow.
o Amount of dissolved gases and viscosity affect the explosiveness of a volcano
Magma composition:
• Higher silica contents = greater viscosity
o Magmas in order of increasing viscosity: basaltic, andesitic, granitic( rhyolitic)
o Granites lavas form short, thick flows
o Basaltic lavas form long, fluid flows(up to 150 km long)
Temperature
• Higher temperature= less viscous flow
• Hot, basaltic magmas are extruded with ease
Conclusion:
• Granitic magmas are more difficult to force through vent
o Vent becomes pluged with viscous magma
o Gases build up, so pressure builds up
o Result: explosive eruption
Dissolved gases
• Provide force that extrudes magma from vent
• Move upwardsconfining pressure lessenssudden release
• Expand to occupy 100s of times their original volume.
Dissolved gas cont’d
• Escape with ease from fluid basaltic magmas propel lava 100s of meters into the air lava fountains-mostly harmless; do not cause great loss of life or property
• Viscous magmas impede upward movementgas pockets increase, so more...