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Volcanoes - PowerPoint PPT Presentation

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Volcanoes. Volcanic eruptions are among the Earth's most powerful and destructive forces.

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PowerPoint Slideshow about 'Volcanoes' - garth

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Presentation Transcript
Volcanic eruptions are among the Earth's most powerful and destructive forces.
  • Volcanoes are also creative forces. The Earth's first oceans and atmosphere formed from the gases given off by volcanoes. In turn, oceans and an atmosphere created the environment that made life possible on our planet.
why do volcanoes erupt
Why Do Volcanoes Erupt?
  • Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma.
  • Magma is lighter than the solid rock around it, magma rises and collects in magma chambers.
  • Eventually some of the magma pushes through vents and fissures in the Earth's surface. A volcanic eruption occurs!
where do volcanoes erupt
Where Do Volcanoes Erupt?
  • Tectonic plates float on a softer layer of rock in the Earth's mantle. As the plates move about they push together or pull apart. Most volcanoes occur near the plates boundaries.
  • Some volcanoes occur in the middle of plates at areas called hotspots- places where magma melts through the plate and erupts.
3 main types of volcanoes
3 Main Types of Volcanoes
  • Stratovolcanoes
  • Cinder cones
  • Shield volcanoes
  • Build from eruptions of lava that pile up in layers or strata (much like layers of cake and frosting)
  • These volcanoes form symmetrical cones with steep sides.
cinder cones
Cinder cones
  • Build from erupting lava that breaks into small pieces as it blasts into the air.
  • As the lava pieces fall back to the ground, they cool and harden into cinders that pile up around the volcano's vent.
  • Cinder cones are very small cone-shaped volcanoes
shield volcanoes
Shield volcanoes
  • Form from eruptions of flowing lava.
  • The lava spreads out and builds up volcanoes with broad, gently sloping sides.
predicting volcanic eruptions
Predicting Volcanic Eruptions
  • Changes in heat flow
  • Changes in shape
  • Earthquake activity
  • Increased gas emissions and steam
why are volcanoes good
Why are volcanoes good?
  • Produced our atmosphere
  • Volcanic soil is very fertile
  • Mineral resources (diamonds, copper, gold, pumice, bbq rocks)