Chapter 9: Volcanoes

1. Chapter 9: Volcanoes 9.1: How and Where Volcanoes Form 9.2: Magma and Erupted Materials 9.3: Volcanic Landforms 9.4: Extraterrestrial Volcanism

2. 9.1: How and Where Volcanoes Form Volcano-Refers to both the opening in Earth's crust through which molten rock, gases and ash erupt and to the landform that develops around this opening.

3. 9.1: How and Where Volcanoes Form • Magma Formation 1. Three main conditions for magma to form: • A decrease in pressure can lower melting temperatures. • An increase in temperature can cause materials in the Asthenosphere to melt. • An increase in the amount of water can lower melting temperatures.

4. 9.1: How and Where Volcanoes Form 2. Most volcanoes are found along mid-ocean ridges and along Subduction boundaries. 3. Most magma is less dense than the surrounding rocks and therefore rises to the surface.

5. 9.1: How and Where Volcanoes Form • At Subduction Boundaries • Oceanic-Oceanic and Oceanic-Continental. See diagram on page 195. • Create Volcanoes. • At Divergent Boundaries • Plates split apart and magma oozes up, creating ridges. • Mostly occurs in the middle of oceans.

6. 9.1: How and Where Volcanoes Form D. Over Hot Spots • Hot spot- Areas of volcanic activity that result from plumes of hot solid material that have risen from deep with the Earth's mantle. • Hot spots stay in the same place as the plates continue to move. See page 197. • Volcanic islands forming over a hot spot.

7. 9-2 Magma and Erupted Materials • Types of Magma • Viscosity-resistance to flow. Determined by silica content. Higher the silica, slower the flow. • Gases can create explosive volcanoes. • See summary on page 199. • Lava Flows • Lava-Magma that reaches the surface • Basaltic lava flows are usually slow and non-explosive. There are two main types: Pahoehoe (ropey) and AA (sharp). • Pillow Lava- rounded lumps of lava formed underwater.

8. 9-2 Magma and Erupted Materials • Ash and Rock Fragments • Pyroclastic Material- When gases are released; solid fragments of this material are ejected. • These materials are classified by size. Ash is less than 2 mm. Lapilli ranges in size from 2-64 mm and blocks or bombs are greater than 64 mm. • Pyroclastic Flow- A dense superheated cloud that travels downhill with amazing speed (100 kph).

9. 9.3: Volcanic Landforms • Shield Volcanoes • Low viscosity lava that flows for long distances. • Lava builds up in layers and forms broad bases and gentle slopes.

10. 9.3: Volcanic Landforms B. Cinder Cones • The simplest of the volcanoes occurs when lava is thrown from the volcano. • Lava hardens before it hits the ground and accumulates forming a cone shaped mound.

11. 9.3: Volcanic Landforms • Composite Cone • Develops when layers of material from several volcanic events accumulate around a vent. • The materials include both hardened lava and pyroclastic material. • Lahar-A fast moving mudflow created by a volcanic eruption.

12. 9.3: Volcanic Landforms D. Caldera • When magma beneath a volcano is released after the top of the volcano collapses, forming a large crater shaped basin. • Examples are Crater Lake in Oregon and Yellowstone NP. See page 204. E. Lava Plateaus • Basaltic lava pouring from fissures and spreading across the land. • Volcano • Volcanic Landforms

13. 9.4: Extraterrestrial Volcanism • The Moon • Dark areas on the moon are basaltic lava flows. • Volcanism began about 3-4 billion years ago. • Mars • Home to Olympus Mons, the largest volcano in the solar system. • It measures 600 km across and 27 km above the surrounding terrain

14. 9.4: Extraterrestrial Volcanism • Venus • Has 1600 large volcanoes • Some volcanoes may still be active

15. 9.4: Extraterrestrial Volcanism D. Io (Jupiter’s 3rd moon) • One of the most volcanically active areas in the solar system. • Io is caught in a tug of war, which creates friction and then heat. That heat drives the volcanic activity.