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Chapter 7: Volcanoes

Chapter 7: Volcanoes. New Vocabulary Lava - magma (or hot, liquid rock) that reaches the surface Pyroclasts - hot rock fragments (from the Greek word “pyro” meaning fire and “clast” meaning broken)

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Chapter 7: Volcanoes

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  1. Chapter 7: Volcanoes

  2. New Vocabulary Lava- magma (or hot, liquid rock) that reaches the surface Pyroclasts- hot rock fragments (from the Greek word “pyro” meaning fire and “clast” meaning broken) Pyroclastic flows- mixture of gases and pyroclastic debris. It is so dense that it hugs the ground

  3. What is a volcano? A volcano is a hill or mountain formed when lava or other molten rock reaches the surface. However, very fluid lava may reach the surface and harden into a horizontal layer. Videos Volcano 101 Geological Journey (start at about 28:00 mark)

  4. Why is volcanic activity important to geology? • Landforms are created • Landforms are destroyed (less common) • Provides clues about the interior of the Earth

  5. How does volcanic activity affect humans? • Growth of landforms (ex. Hawaii) • Produces new rock & fertile soil • Tourist attraction • Hawaii is built from a seamount (or magma plume); taller than Mt. Everest 2. Geothermal energy

  6. Effects on weather • In 1991, Mt. Pinatubo dropped the average temperature by 0.5°C for several years because of fine volcanic ash • The 1815 eruption of Tambora in Indonesia caused a very cold summer in 1816 (snow and frost in New England in the summer)

  7. Volcanic catastrophes • Eruption of Mt. Vesuvius destroyed Pompeii (much death caused by 5-8 m of hot ash) • Krakatoa (Indonesia) exploded and caused a tsunami that killed 34,000 • Mt. St. Helen’s in Washington State, USA • Volcanoes can kill because of pyroclastic flows, famine (because of crop destruction), pyroclastic fragments and ash (roof collapses)

  8. What determines the severity of a volcanic event? There are two things that determine the severity of a volcanic event: • Amount of gas in the lava or magma • The ease or difficulty with which the gas escapes. This is determined by the viscosity (or “thickness”) of the lava. *Overall, the more viscous the lava and the greater the volume of gas trying to escape, the more violent the eruption

  9. What determines the severity of a volcanic event? Low viscosity (more like liquid): • Less silica (ex. basaltic rock) • Less violent eruptions • Ex. Hawaii High viscosity (thick): • More silica (ex. rhyolite) • More violent eruptions • Ex. Mount St. Helens

  10. What kinds of rocks do volcanoes produce? All volcanic rocks are extrusive and most have fine-grained crystals because of quick cooling. Common volcanic rocks include the following: • Rhyolite • Andesite • Dacite • Basalt • Obsidian (black volcanic glass) • Pumice (frothy glass; floats in water; good for pedicures) • Rocks with holes (like Swiss cheese) • Volcanic bombs

  11. What are the characteristics of different types of volcanoes? First of all, some new volcano lingo: • Vent: opening through which an eruption takes place • Crater: basin-like depression over a vent at the top of a volcano • Caldera: a volcanic depression much larger than the original crater and having a diameter of at least 1km

  12. Caldera (Crater Lake, USA) Vent Crater

  13. Three major types of volcanoes: Shield Volcano: • Broad, gentle slopes • Lava spreads widely and thinly • Made of solidified layers of lava flows • Ex. Hawaiian Islands

  14. Pyroclastic cones: • Made of pyroclastic fragments (chunks of material) • Steep slopes • Less common; tends to wear away quickly • Less than 500m high

  15. Composite volcanoes: • Made of alternating layers of pyroclastic fragments and solidified magma flows • Steeper than shield volcanoes, but not as steep as pyroclastic cones • Built over many years; can be old and very large • Mostly found around the “Ring of Fire” and the Mediterranean Belt • Ex. Mount St. Helens; Mt. Vesuvius; Mt. Etna Mt. Vesuvius Video

  16. Flashcard Quiz • Click Here!

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