2. VOLCANOES 21.2

3. What is a volcano? Volcano: opening in the Earth’s crust where magma erupts onto the surface Magma: molten rock underground Lava: magma that has reached Earth’s surface

4. How Does A Volcano Form?  Under certain conditions, small amounts of mantle rock can melt, forming liquid magma. The magma rises upward through the crust, erupting at the surface as a volcano.

5. Structure of a Volcano

6. 3 Factors That Determine the Viscosity of Magma:  1. Temperature – the higher the temperature, the lower the viscosity  2. Water Content – the more water, the lower the viscosity  3. Silica Content – the higher the silica content, the higher the viscosity. Silica acts like glue.

7. TYPES OF LAVA  Felsic - high silica content - light colored - slow moving - explosive eruptions  Mafic - low silica content - dark colored - fast flowing lava - quiet eruptions

8. LAVA FRAGMENTS  Tephra: solid fragments of lava - ash: less than 2mm diameter - lapilli: 2 – 64mm diameter - bombs: 64mm or higher diameter

9. Ash Lapilli Bombs

10. OTHER LAVA FRAGMENTS  aa – broken, sharp blocks of lava  Pahoehoe – smooth, wrinkled lava

11. VOLCANO ZONES  Pacific Ring of Fire - zone around the Pacific Ocean - most active area of volcanoes in World  Mid-Ocean Ridges - zone along divergent plates  Eurasian Belt - zone along south border of Eurasian plate

12. Hot Spots  A hot spot is a region where hot rock extends deep within the mantle to the surface.  Example: Hawaii

13. 3 TYPES OF VOLCANOES

14. 1. CINDER CONE  Steep sides  Smallest, most abundant  Active for a short time, then become dormant

15. 2. COMPOSITE  Consists of alternating layers of ash, cinders, and lava  Steep sides  Thick magma  Lot of gases

16. 3. SHIELD  Consists of layers of mafic lava  Gently sloping sides, wide base

17. FAMOUS ERUPTIONS  Vesuvius, Italy – 79 A.D.  Krakatau, Indonesia – 1883  Mount St.Helens, U.S. – 1980  Mt. Pinatubo, Phillipines – 1992  Eyjafjallajökull volcano in Iceland – April, 2010

18. Mt. Vesuvius

19. Mt. Krakatau 1883

20. Mt. St.Helens 1980 BEFOREAFTER

21. Mt.Pinatubo 1992

22. Mt.Kilaeau Present

23. VOLCANOES IN OUTER SPACE  The Moon – no volcanoes  Mars - Olympus Mons - 3 times higher than Mt.Everest  Io - Moon of Jupiter - volcanic activity