Ch. 18 Volcanoes

Ch. 18 Vocabulary Viscosity Tepha Vent Hot Spot Caldera Cinder-Cone Volcano Composite Volcano Pyroclastic Flow Shield Volcano Crater

Magma Proves that earth is geologically active Magma formed deep within earths surface Temperatures must be high enough to melt rock - 800-1200 oC Temperatures increase with depth Pressure increase with depth Increase Pressure – Decrease melting point B/C Magma is less dense than surrounding rock, Magma rises to surface

Magma Composition Viscosity Silica content Water content Resistance to flow Hotter the magma, lower the viscosity Silica content Determines viscosity High content – high viscosity Water content High amounts of water will evaporate, build pressure More explosive Three Types of Magma

Magma Types Basaltic Andesitic Rhyolitic Low Viscosity (50% Silica) Quiet Eruptions Andesitic Intermediate Viscosity (60% Silica) Intermediate Eruptions Rhyolitic High Viscosity (70% Silica) Great Eruptions

Volcano Locations: Ring of Fire

Anatomy of a Volcano Vent Cone (1 km wide) or Caldera (50 km wide) Magma reaches the surface and lava erupts out of a vent Lava solidifies and builds up mountain around vent Cone (1 km wide) or Caldera (50 km wide)

Types of Volcanoes Shield Broad gently sloping sides Layer upon layer of basaltic lava accumulation (non-explosive) Low viscosity

Types of Volcanoes Cinder Cone Material exploded high into the air and comes back to earth Steep side from explosive eruptions More viscous lava contains more gases which fuel more explosive eruptions

Types of Volcanoes Composite Volcanic fragments and lava eruptions – most common Contains large amounts of silica, water, and gases Potentially dangerous to people and environment

Other locations for Volcanoes Hot Spots Located away from plate boundaries High temperature mantle plumes rise towards the surface Hawaiian Islands