Published on

Volcanoes Form as Molten Rock Erupts

Published in: Education, Technology
1 Like
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide


  1. 1. Volcanoes Form as Molten Rock Erupts Pages 146-153 (section B)
  2. 2. What is a Volcano? <ul><li>Volcano - an opening in the Earth’s crust through which molten rock, rock fragments, and hot gasses erupt. </li></ul><ul><ul><li>A mountain built up from erupted material is also called a volcano. </li></ul></ul>
  3. 3. What happens when a volcano erupts? <ul><li>Volcanoes may erupt violently or gently </li></ul><ul><li>Even if no magma reaches the surfaces volcanoes can be dangerous </li></ul><ul><ul><li>Hot rocks can fly out starting fires </li></ul></ul><ul><ul><li>Rocks can land on roofs in large numbers causing the roofs to collapse </li></ul></ul>
  4. 4. Magma <ul><li>Magma contains silica and gases </li></ul><ul><li>Magma HIGH in silica is resistant to flowing </li></ul><ul><ul><li>Causes violent eruptions </li></ul></ul><ul><li>Magma LOW in silica flows easily </li></ul><ul><li>Magma rises as long as it is less dense than the surrounding rock. </li></ul><ul><li>When magma erupts it is called lava </li></ul>
  5. 5. Volcanoes
  6. 6. Volcanoes
  7. 7. Rock Fragments <ul><li>Fragments form as: </li></ul><ul><ul><li>Escaping gas bubbles pop, tearing magma apart </li></ul></ul><ul><ul><li>Larger pieces of lava are thrown into the air, cooling and hardening during flight </li></ul></ul><ul><ul><li>Rocks of all sizes rip loose from volcanoes’ walls during eruptions </li></ul></ul>
  8. 8. Rock Fragments <ul><li>Tiny rock fragments form volcanic ash , sized between dust fragments and grain of rice. </li></ul><ul><ul><li>Stay in the air a long time, but travel far distances </li></ul></ul><ul><li>Cinders are larger than ash, smaller than bombs </li></ul><ul><li>Bombs are the largest size rock fragments </li></ul><ul><ul><li>Fall the fastest </li></ul></ul>Ash Cinder Bomb
  9. 9. Volcanic Gases <ul><li>What looks like smoke coming from a volcano is actually a mixture of ash and gases. </li></ul><ul><ul><li>The main gases in magma are water vapor and carbon dioxide </li></ul></ul>
  10. 10. Pyroclastic Flow <ul><li>Volcanic gases can mix with rock fragments and stay near the ground. </li></ul><ul><li>Pyroclastic flow- a dense cloud of superhot gases and rock fragments. </li></ul><ul><ul><li>Can reach temperatures of 800 degrees C (1500 degrees F) </li></ul></ul><ul><ul><li>Can reach speeds of 160 km/hr (100 mi/hr) </li></ul></ul><ul><ul><li>Pyroclastic flows are the most dangerous type of volcanic eruption. </li></ul></ul>
  11. 11. Most volcanoes form along plate boundaries <ul><li>Most of Earth’s volcanic activity takes place under water- along plate boundaries </li></ul><ul><li>Volcanoes can also occur along hotspots away from plate boundaries- this is less common </li></ul>
  12. 12. Types of Volcanoes <ul><li>Shield Volcano – shaped like a broad, flat dome. </li></ul><ul><li>Built up by man eruptions of lava that is relatively low in silica. </li></ul>
  13. 13. Types of Volcanoes <ul><li>Cinder Cone- a steep, cone-shaped hill formed by the eruption of cinders and other rock fragments that pile up around a single crater. </li></ul><ul><li>Form as gas-rich magma erupts- often on the side of another volcano </li></ul><ul><li>Ten to hundreds of meters tall </li></ul>
  14. 14. Types of Volcanoes <ul><li>Composite Volcano - a cone shaped volcano that is built up of layers of lava and layers of rocks fragments. </li></ul><ul><li>Steep at the top flattens out at the bottom </li></ul><ul><li>Tends to have very violent eruptions </li></ul>
  15. 15. Caldera <ul><li>Caldera- a huge crater formed by the collapse of a volcano when magma rapidly erupts from underneath it. </li></ul>
  16. 16. Active Volcano <ul><li>A volcano that currently vents lava or gases etc, or has the capability of doing so </li></ul>
  17. 17. Dormant Volcano <ul><li>A volcano that has not erupted for a considerable length of time, but is still capable of erupting </li></ul>
  18. 18. Warning Signs of Volcanic Activity <ul><li>Temperature of rocks in the volcanic cone increases </li></ul><ul><li>The cone may change shape- swell or bulge just before eruption </li></ul><ul><li>Small earthquakes and tremors in the area around the volcano </li></ul><ul><li>Emission or increase of gas from the volcano </li></ul><ul><li>Often animals may act strangely before the eruption </li></ul>
  19. 19. Scientist Monitor Volcanoes <ul><li>Scientist cannot prevent volcanoes from erupting </li></ul><ul><li>The signs of an eruption can allow people to leave an area so the loss of human life can be minimized </li></ul>
  20. 20. <ul><li>http://www.snagfilms.com/films/title/volcano_natures_inferno/ </li></ul>