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Volcanoes

Volcanoes. OBJECTIVES: Types of Magma Anatomy of a Volcano Types of Volcanoes. Viscosity. Viscosity : Resistance of a liquid to flow There are 3 types of magma. They range from very runny (low viscosity) to very sticky (high viscosity). Anatomy of a Volcano.

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Volcanoes

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  1. Volcanoes OBJECTIVES: Types of Magma Anatomy of a Volcano Types of Volcanoes

  2. Viscosity • Viscosity: Resistance of a liquid to flow • There are 3 types of magma. They range from very runny (low viscosity) to very sticky (high viscosity).

  3. Anatomy of a Volcano • Lava erupts through an opening called a vent. • Over time, the cooled & solidified lava forms a mountain known as a volcano. • At the top of the volcano, there is a bowl-shaped depression that can vary in size: • Crater: Smaller in size • Caldera: Larger in size. • Over 1 km in size • Forms when top of volcano collapses into the magma chamber.

  4. Anatomy of a Volcano • Volcanic fragments thrown into the air during eruptions are called tephra. • Can be newly cooled & hardened lava, crystallized mineral grains, or pieces of volcanic cone. • Categorized based on size. • Dust Size: Small • Volcanic Bombs: Large, rounded tephra. • Volcanic Blocks: Large, angular tephra.

  5. Anatomy of a Volcano • Pyroclastic flow are clouds of gas, ash, & other tephra down a slope at incredible speeds. • A.K.A. Rapidly moving volcanic material! • Can cause death & tremendous damage!

  6. Types of Volcanoes • Shield • Cinder-Cone • Composite (Stratovolcano)

  7. Shield Volcano • Gently sloping sides • Nearly circular base • Forms when layers of basaltic lava accumulate during non-explosive eruptions • Low viscosity magma: Basaltic Magma • Ex. Hawaiian Islands

  8. Cinder-Cone Volcano • Forms when material ejected high into the air falls and piles up around the vent. • Usually has steep sides • Generally small in height • Has more silica than shield and large volumes of gases • Explosions are more severe than shields: Andesitic Magma

  9. Composite Volcanoes • Forms when layers of volcanic fragments alternate with lava. • Large amounts of silica and gas: Rhyolitic magma. • Much larger than cinder-cone. • Violently explosive: Harmful to humans & environment • Ex. Mt. Saint Helens

  10. Where Do Volcanoes Occur? • Most occur at plate boundaries • 80% along convergent • 15%along divergent • 5% occur far from plate boundaries.

  11. Convergent Volcanism • Circum-Pacific Belt • A.K.A. “Ring of Fire” • Volcanoes of the Western U.S., Japan, Philippines, & Indonesia • Ex. Mt. Saint Helens • Mediterranean Belt • Volcanoes of Italy • Mt. Vesuvius

  12. Ring of Fire

  13. Divergent Volcanism • Most occur along ocean ridges. • Plates are pulling apart and magma wells up into the gap, producing volcanoes and lava flows.

  14. Hot Spots • The volcanoes that are formed far from plate boundaries are formed because of hot spots. • Hot Spots: areas of intense magma temperatures. • As a plate moves over a hot spot, the temperatures melt the crust and the new magma rises to form volcanoes. • When this happens, you get a string of volcanoes • Ex. Hawaiian Islands

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