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Volcanoes - PowerPoint PPT Presentation

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Volcanoes

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  1. Volcanoes Erupting with fun!

  2. Magma vs. Lava • Magma is liquid rock produced under the Earth’s surface but Magma becomes Lava as soon as it leaves the Earth and flows outside. Lava Magma

  3. Magma Magma can form under three conditions: 1. If rock temperature risesabove its melting point then it will melt into magma 2. Rock can melt when too much pressure is removed from rock that is above its melting point 3. The addition of fluids, such as water, may lower the melting point of some rock and cause it to melt

  4. Volcanism • Volcanism is any activity that includes the movement of magma onto Earth’s surface • Avolcanois a vent or fissure in Earth’s surface through which magma and gases are expelled

  5. Location and Formation Of Volcanoes Most volcanoes occur in convergent and divergent boundaries of tectonic plates A major zone of active volcanoes is located in the “Pacific Ring of Fire” which is also a major earthquake zone

  6. Locations of Volcanoes Some tectonic boundaries include: • Subduction Zones • Mid-Ocean Ridges • Hot Spots

  7. Subduction Zones A subduction zone is where one tectonic plate moves under another

  8. Mid-Ocean Ridges • A long, undersea mountain chain that has a steep, narrow valley at its center. • Forms as magma rises from the asthenosphere • Creates new ocean floor as tectonic plates move apart (sea floor spreading)

  9. Hot Spots • Areas of volcanism within the interiors of lithospheric plates • The Hawaiian Islands were created by a hot spot • See HOT demo!

  10. Types of Volcanic Eruptions • Quiet volcanoes have mafic magma which is rich in magnesium and iron. Mafic magma is dark in color with runny lava • Explosive volcanoes have felsic magma which is rich in light-colored silicate materials and is thick and sticky. Compare water boiling (quiet volcano) to thick spaghetti sauce boiling (explosive volcano)

  11. Pyroclastic Materials • “Pyro” means fire • Pyroclastic materials include fragments of rock that form during volcanic eruptions

  12. Types of Pyroclastic Materials (from smallest to largest • Volcanic dust • Volcanic ash • Lapilli—means little stones…they normally fall near the vent • Volcanic bombs—clots of lava that are thrown out of the volcano & become round or spindle shaped as they go through the air • Volcanic blocks—solid rock that is blasted through the vent…some are as big as a house!!

  13. Read “What Volcanoes Can Produce”

  14. Types of Volcanoes • Shield volcanoes • Cinder Cones • Composite Volcanoes (Stratovolcanoes) • Calderas

  15. Shield Volcanoes • Wide base • Gently sloping sides • Forms from quiet eruptions

  16. Cinder Cone Volcanoes • Steep slopes • Form from explosive eruptions and are made of pyroclastic materials

  17. Composite Volcanoes(Stratovolcanoes) • Made with alternating layers of hardened lava flows and pyroclastic materials • This type of volcano alternates quiet and explosive eruptions

  18. Calderas • This type of volcano is created when the magma chamber below a volcano empties and the cone collapses • The collapse leaves a large basin-shaped depression (crater) • Some calderas eventually fill with water to become lakes

  19. Read “What Are Volcanoes?” and answer questions