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Volcanoes - PowerPoint PPT Presentation

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Volcanoes. Volcanoes.

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DefinitionA volcano is an opening, or rupture, in a planet's surface or crust, which allows hot, molten rock, ash, and gases to escape from below the surface. Volcanic activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time.


TypesThere are 5 general types of volcanoes:

1. Caldera volcanoes2. Cone volcanoes3. Lava Dome volcanoes4. Shield volcanoes5. Strato volcanoes



Lava Dome


Strato or Composite


Types of Eruptions1. Effusive (Hawaii)

2. Explosive (Yellowstone or Mt. St. Helens)

a) Pyroclastic Flowb) Phreatic Eruptionc) Plinian Eruptiond) Strombolian Eruptione) Vulcanian Eruption



The Volcano Explosivity Index (VEI) provides a relative measure of the explosiveness of volcanic eruptions. The scale is based on:

  • Volume of products erupted

  • eruption cloud height

  • qualitative observations


Plate Tectonics

  • Volcanoes are NOT randomly distributed across the globe

  • They are concentrated along narrow zones

  • Most volcanoes (~80% or more) occur along plate boundaries

  • Interior of plates are mostly volcanoe free

  • Volcanoes help to define plate boundaries

  • Volcanoes form Hot Spots



1. tephra (ash fallout)

2. pyroclastic flows (Mt. Unzen, Japan)

3. tsunamis (Krakatau)

4. mass wasting (landslides)

5. lahars (volcanic mudflows)

6. lava flows (Hawaii)

7. gas emissions (Mammoth Lakes)

8. directed blast (Mt. St. Helens)

9. pyroclastic surge (less dense than pyroclastic flows)



  • Industrial and chemical uses (pumice is a natural glass used for grinding, polishing, cleaning)

  • Volcanic rock is sometimes used in road construction

  • Volcanic ash that has weathered greatly has improved soil fertility

  • Volcanic material is the source of opal

  • Volcanic material is also the source of metals such as gold, silver, molybdenum, copper, zinc, lead, and mercury

  • Some volcanic gas include water vapor – part of the water cycle

  • Volcanoes also are tourist attractions and support local tourist economies



  • It is important to study volcanoes due to the loss of life and damage to property they can cause

  • They also have multiple benefits

  • Human population continues to grow and many cities are cited along plate boundaries

  • Education is the key to being prepared for volcanoes


Volcanoes occur due to molten rock reaching the earth’s surface; they are measured using the VEI scale; they occur along plate boundaries; they cause pyroclastic and lava flows, ash fallout, lahars, mass wasting, earthquakes, and may cause tsunamis, all of which may cause loss of life and damage to property

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