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VOLCANOES

VOLCANOES. Volcano Basics. Definition of Volcano Mountain that forms when molten rock (magma) is forced to the Earth’s surface Number of active volcanoes = ? 20 erupting right now (50-60/year) (160/decade) Number of volcanologists - 1,500. WHERE DO VOLCANOES FORM?.

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VOLCANOES

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  1. VOLCANOES

  2. Volcano Basics • Definition of Volcano • Mountain that forms when molten rock (magma) is forced to the Earth’s surface • Number of active volcanoes= ? • 20 erupting right now(50-60/year) (160/decade) • Number of volcanologists - 1,500

  3. WHERE DO VOLCANOES FORM? •mid ocean ridges (diverging plate boundaries)

  4. Interior of plates called HOT SPOTS

  5. At subduction zones where tectonic plates collide

  6. ~75% world’s active volcanoes in Ring of Fire

  7. Volcanic Eruptions! •Eruptions can be explosive(kaboom! Kabam!) or effusive (non-explosive and oozing)

  8. Explosive Eruptions • Effusive Eruptions

  9. Explosive vs. Effusive (non-explosive) Depends on the composition of the magma!

  10. In an explosive eruption, the sudden expansion of gases blasts magma into airborne fragments of rock and ash (called tephra). After the initial explosion, quieter eruptions of loosely flowing lava may follow.

  11. What Erupts from a Volcano? • Pyroclastic material • Rock fragments created by eruptions EXPLOSIVE Lapilli Volcanic bombs Volcanic blocks Volcanic ash

  12. Is the type of eruption affected by magma? The thickness (viscosity) of the magma depends on whether it is an explosive eruption or an effusive eruption.

  13. It’s All About the Lava! Lava can be thick or thin, fast or slow.

  14. Ah Ah Lava Flow – thin and flows fast

  15. Pahoe hoe Lava Flow – Slower than Aa and looks like ropes when it dries

  16. Pillow Lava

  17. Blocky Lava Flow Thick and slow

  18. Types of Volcanoes . The three basic types: Shield volcanoes Strato Volcanoes (also called composite) Cinder cones

  19. Shield Volcanoes • Shield volcanoes are broad gently sloping volcanic mountains slowly formed from layers of solidified lava. • Shield volcanoes are formed by effusive eruptions of lava. • Shield Volcanoes can become very large as the lava spreads widely.

  20. MOUNT KILAUEA, HAWAII

  21. MOUNT ETNA, SICILY

  22. Strato Volcanoes (Composite) • Strato Volcanoes are formed from both explosive and effusive eruptions. •Layers of tephra alternating with layers of viscous to watery lava flows createsteep-sided, symmetrical cones that can be very large. •Formed over long spans of time – hundreds of thousands of years of inactivity in between a few years of really intense activity.

  23. MOUNT ST. HELENS, WASHINGTON

  24. Mt. St. Helens Erupting

  25. Cinder Cone Volcanoes • Cinder cones are the smallest volcanoes (< 500’),formed by explosive eruptions of cinder, rock and ash. • Cinder cones are temporary geologic features as they are easily eroded. They have short life spans because the gases causing the violent eruptions is quickly depleted.

  26. Pu`u ka Pele Cinder Cone, Mauna Kea Volcano on Kauai

  27. Can you identify each type of volcano?

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