What is a volcano?

1. What is a volcano? A volcano is an opening, or vent, in the Earth’s crust through which magma and gases are expelled.

2. Where do volcanoes form? • A large number of volcanoes lie directly on tectonic plate boundaries where it is possible for magma to form and rise to the surface. • 80% of active volcanoes form where plates collide. • 15% of active volcanoes form where plates separate. • The remaining volcanoes occur far from any tectonic plate boundary.

3. The plate boundaries in the Pacific Ocean have so many volcanoes that it is known as The Ring of Fire.

4. Volcanoes can also form at subduction zones where temperature and pressure build to create magma.

5. What are the parts of a volcano?

6. Volcanic Eruptions • The composition, or make up, of magma can determine how explosive a volcanic eruption will be. • At this moment eruptions are occurring around the world and on the ocean floor.

7. Non-explosive Eruptions • Most common type of eruption • Produce relatively calm flows of lava • Can release huge amounts of lava • Much of the sea floor is made up of lava from non-explosive eruptions

8. Explosive Eruptions • Occurs much more rarely • Can be incredibly destructive • Expells clouds of hot debris, ash & gas into the air • Instead of lava flows, causes molten rock to be blown into the air where tiny particles harden and fall • Larger pieces of debris fall closer to the volcano • Can blast millions of tons of lava and rock in a matter of seconds, demolishing entire mountain sides

9. Effects of Eruptions • Climate change • Other example: In 1815,Mount Tambora blanketed Indonesia in darkness from the volcanic ash that remained in the atmosphere after it erupted. 12,00 died in the blast, but 80,00 died from resulting hunger and disease. Volcanic ash can blocked the sunlight and caused a drop in temperature, causing crops to fail.

10. Volcanic Landforms Volcanic eruptions can cause profound changes in climate, but they are best known for their volcanic landforms.

11. Shield Volcanoes • Formed from layers of lava released from repeated non-explosive eruptions • Sides are gentle slopes, but can be enormous in size • Hawaii’s Mauna Kea is the tallest mountain on Earth! Measured from its base on the sea floor, it is taller than Mount Everest.

12. Cinder Cone Volcanoes • Made from pyroclastic materials that where usually produced from moderately explosive eruptions • Usually erode quickly because the material is not cemented together. • Small, but has steep slopes • Often occur in clusters, commonly on the sides of other volcanoes

13. Composite Volcanoes (also known asstratovolcanoes) • Most common type of volcano. • Formed from explosive eruptions of pyroclastic materials followed by quieter flows of lava. • Have broad base and sides that get steeper toward the pointed peak.

14. Lava Dome Volcanoes • Formed from thick lava that doesn’t flow far as it pours over and around its vent, or opening.

15. Craters A crater is a funnel shaped pit near the top of the central vent of a volcano.

16. Calderas A large, semicircular depression that forms when the magma chamber below a volcano partially empties and causes the ground to sink.

17. Lava Plateaus A wide flat landform that results from repeated non-explosive eruptions of lava that spread over a large area