Chapter TWELEVE

1. Chapter TWELEVE Volcanoes

2. If green dots are earthquakes and red triangles are volcanoes, What are two things that you notice about their locations??

3. Section 1: Volcanoes and Earth’s Moving Plates What Are Volcanoes? • A volcano is an opening in Earth that erupts gases, ash and lava. • Volcanic mountains form when layers of lava, ash and other material build up around these openings.

4. Section 1: Volcanoes and Earth’s Moving Plates What Are Volcanoes? • Kilauea (kee low AY ah), located in Hawaii, is the world's most active volcano. • The most recent series of eruptions began in 1983 and still continues.

5. Section 1: Volcanoes and Earth’s Moving Plates How Do Volcanoes Form? • Magma is forced upward because it is less dense than the rock around it. • After many thousands or even millions of years, magma reaches Earth's surfaces and flows out through an opening called a vent.

6. Section 1: Volcanoes and Earth’s Moving Plates How Do Volcanoes Form? • As lava flows out, it cools quickly and becomes solid, forming layers of igneous rock around the vent. • The steep walled depression around a volcano's vent is called a crater.

7. Section 1: Volcanoes and Earth’s Moving Plates Where Do Volcanoes Occur? • Divergent Plate Boundaries • The mid-Atlantic ridge is an area where the plates are moving apart. • When plates separate, they form long, deep cracks called rifts. • Lava flows from these rifts and is cooled quickly by sea water.

8. Section 1: Volcanoes and Earth’s Moving Plates Where Do Volcanoes Occur? • Sometimes, the volcanoes and rift eruptions rise above sea level, forming new islands such as Iceland. • In 1963, the new island Surtsey was formed during a volcanic eruption.

9. Section 1: Volcanoes and Earth’s Moving Plates Where Do Volcanoes Occur? • Convergent Plate Boundaries • Forms volcanoes where an oceanic plate slides below a continental plate. • Magma forms when the plate sliding below another plate gets deep enough and hot enough to melt partially and the magma is then forced upward to the surface. • Volcanoes that form at convergent plate boundaries erupt more violently than other volcanoes do.

10. Section 1: Volcanoes and Earth’s Moving Plates Where Do Volcanoes Occur? • Hot spots • Form when areas between the Earth's mantle and core are unusually hot and rock at these areas is forced toward the crust where it melts partially. • Magma breaks through the crust to form several volcanoes. • Not at a plate boundary • Formed Hawaiian islands

11. Section 2: Types of Volcanoes What Controls Eruptions? • Trapped gases like water vapor and carbon dioxide build up in volcanoes. • If the gas escapes easily, it is a quiet eruption. • If gas and water vapor build up, eruptions can be explosive

12. Section 2: Types of Volcanoes Composition of Magma • Quiet eruptions: magma that is low in silica and is basaltic. • Has lava that pours from volcanic vents and runs down the sides of a volcano

13. Section 2: Types of Volcanoes Composition of Magma • Explosive eruptions: magma that is high in silica and is andesitic. • Has magma that is thick and when pressure builds up an explosion occurs. It often carries pieces of lava.

14. Section 2: Types of Volcanoes Forms of Volcanoes • Shield Volcano • Broad, gently sloping volcano formed by quiet eruptions of basaltic lava. • The basaltic lava flows over Earth's surface covering large areas with deposits of basaltic igneous rocks when it cools.

15. Section 2: Types of Volcanoes Forms of Volcanoes • Shield Volcano • Accounts for the greatest volume of erupted volcanic material. • Much of the new seafloor that originates at the mid-ocean ridge forms as underwater flood basalts.

16. Section 2: Types of Volcanoes Forms of Volcanoes • Cinder Cone Volcano • Steep-sided, loosely packed volcano formed when tephra falls to the ground. • Tephra: bits of rock or solidified lava dropped from the air after an explosive eruption. • Vary in sizes from volcanic ash, cinders, large rocks and blocks.

17. Section 2: Types of Volcanoes Forms of Volcanoes • Composite Volcano • Volcano built by alternating explosive and quiet eruptions that produce layers of tephra and lava. • Found mostly where Earth's plates come together and one plate sinks below the other.

18. Section 3: Igneous Rock Features Intrusive Features • Batholiths: large intrusive rock body that forms when magma being forced upward toward Earth's crust cools slowly and solidifies underground. • Dikes: magma that is forced into a crack that cuts across rock layers and hardens. • Sills: magma that is forced into a crack parallel to rock layers and hardens.

19. Section 3: Igneous Rock Features Forms of Volcanoes

20. Section 3: Igneous Rock Features Other Features • Volcanic neck: solid igneous core of a volcano left behind after the softer cone has been eroded. • When a volcano stops erupting, the magma hardens inside the vent. • Erosion, usually by water and wind, begins to wear away at the volcano.

21. Section 3: Igneous Rock Features Other Features • Caldera: large circular-shaped opening formed when the top of a volcano collapses. • Crater Lake in OR is a caldera that filled with water and is now a lake.

22. Section 3: Igneous Rock Features Effects of Eruptions • Examples of destruction: • Lava flows destroy everything in their path. • Falling volcanic ash can collapse buildings, block roads and can cause lung disease in people and animals. • Volcanic ash and debris rush down the side of a volcano: pyroclastic flow.

23. Section 3: Igneous Rock Features Effects of Eruptions • Examples of destruction: • Temperature inside a pyroclastic flow can be high enough to ignite wood. • Sulfurous gases from volcanoes can mix with water vapor in the atmosphere to form acid rain.

24. In your notes, create a diagram of a volcano. It must include the following features (with correct lables): • Ash cloud • Pyroclastic flow • Tephra • Layers of ash • Layers of lava • Crater • Main vent • Dike • Sill • Magma chamber