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Chapter 18 - Volcanoes

Chapter 18 - Volcanoes. I. Magma. Formation Temperature increases with depth Increased pressure increases melting point Increased water content decreases melting point. B. Types of Magma 1. Basaltic – rich in iron & magnesium, melts around 1000 o C. Quiet eruptions

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Chapter 18 - Volcanoes

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  1. Chapter 18 - Volcanoes

  2. I. Magma • Formation • Temperature increases with depth • Increased pressure increases melting point • Increased water content decreases melting point

  3. B. Types of Magma 1. Basaltic – rich in iron & magnesium, melts around 1000o C. Quiet eruptions Oceanic crust 2. Rhyolitic – high silica content; high water and gas content; explosive! Continental crust 3. Andesitic – mixture of basaltic & rhyolitic, found along continental margins

  4. C. Viscosity 1. Definition – resistance to flow 2. Basaltic=low viscosity (runny) 3. Rhyolitic=high viscosity (does NOT flow well)

  5. II. Volcanoes • Anatomy of a volcano • Vent- opening in crust; magma leaves earth and becomes lava • Crater- as lava accumulates, mountain forms. The bowl-shaped depression at the top is the crater • Caldera- once the magma chamber empties out, the mountain may collapse.

  6. B. Volcanic Landforms 1. Shield a. broad, gently sloping sides b. basaltic lava c. Example; Mauna Kea in Hawaii 2. Cinder a. steep sides, short b. rhyolitic lava; very explosive c. Example; Izalco in El Salvador 3. Composite a. steep top, gently sloping base b. andesitic lava c. Example; Mt. St Helens

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