1. 19.4: Volcanoes

2. Objectives  Describe different types of volcanoes  Explain how and where volcanoes occur

3. Active and Extinct Volcanoes

4. Magma vs. Lava  Underground liquid rock  Once magma has broken the earth’s surface, it becomes lava

5. Types of Volcanoes  Shield Volcanoes  Composite Volcanoes  Cinder Cones

6. Shield Volcanoes  Magma rich in iron and magnesium is very fluid and flows easily  Eruptions are mild  Builds a gently sloping mountain  Hawaii

7. Shield Volcanoes

8. Composite Volcanoes  Alternating layers of ash, cinders, and lava  Magma rich in silica is thicker and traps gases  Gases in magma cause more explosive eruptions  Mt Fuji, Mt St Helens, Mt Hood, Mt Shasta, Mt Rainier

9. Composite Volcanoes

10. Cinder Cones  Smallest and most abundant type  Violent eruptions from lots of trapped gas  Short lifespan  Mt Paricutin in Mexico  First erupted in 1943  In 2 years was 450 meters tall  Stopped erupting in 1952

11. Cinder Cones

12. Supervolcanoes

13. If you haven’t been to Yellowstone – you need to go

14. My favorite – the mudpots

15. Yellowstone’s Debris Zones

17.  Colossal sized eruptions  Earth Changing  Currently 7 known, 3 in US  We are finding more

18. Now total 8  The Discovery Channel has documented seven known supervolcanoes  Yellowstone (Wyoming),  Long Valley (Mammoth, California),  and Valles Calderas (New Mexico) in the US;  Lake Toba, North Sumatra, Indonesia;  Taupo Volcano, North Island, New Zealand;  Aira Caldera, Kagoshima Prefecture, Kyūshū, Japan;  and the Siberian Traps, Russia  The newest: Sesia Valley Caldera in Northern Italy

19.  Valle Caldera, New Mexico

20. Volcanoes form along plate boundaries and above hot spots  Openings in the earth’s crust are called vents

21. Volcanoes at Convergent Plate Boundaries  75% of all active volcanoes on Earth are located on Convergent Plate Boundaries  The Pacific “Ring of Fire”  The sinking ocean plate melts and magma rises to the surface  The lava is cooler, sticky and gaseous  Forms Composite volcanoes

22. Volcanoes on Divergent Plate Boundaries  Magma rises to fill the gap, forming ridges around a central valley  San Luis Valley is formed this way  Mid-Atlantic Ridge and Iceland

23. Volcanoes on Hot Spots  Some volcanoes form in the middle of plates  The form above mantle plumes  Hawaiian Islands  Yellowstone