1. Volcanoes

2. Volcano Stats Definition of Volcano –Mountain that forms when molten rock (magma) is forced to the Earth’s surface Number of active volcanos = ? 1,300 – 1,500 –20 erupting right now (50-60/year) (160/decade) Number of volcanologists = 1,500

3. Why Volcanoes Occur? Temperatures in the mantle are hot enough to melt rock into magma. Less dense than the solid rock around it, magma rises and some of it collects in magma chambers. As the magma rises, pressure decreases allowing trapped gasses to expand and propel the magma through openings in the Earth’s surface causing an eruption. Erupted magma is called lava.

4. What causes volcanoes?

5. Hot Spots

6. Where Volcanoes Form Tectonic Plate Boundaries!!! ~75% world’s active volcanoes in Ring of Fire Highlight the places where volcanoes form on the map in your notes! Also, answer the 1 st question as to why volcanoes form here!

8. Magma vs. Lava Magma is molten rock beneath the surface. Lava is erupted magma. There are 2 types of lava: – A a (ah ah) is largely solidified rock that gets pushed forward. – Pahoehoe (pah hoy hoy) is flowing “liquid” with a ropy, billowy surface

9. What Erupts from a Volcano? Lava can be thick or thin. Blocky lava Pahoehoe Aa Pillow lava

10. Volcanic Eruptions Effusive Eruptions - outpouring of lava without significant explosive eruptionlava Explosive Eruptions - gas-driven explosions that propels magma and tephra (small fragments of material)magmatephra

11. The Composition of Magma Determines whether it is explosive or not! High water content –More likely to be!!! High content –More likely to be !!! –Why? Silica has a thick, stiff consistency –Flows slowly –Tends to harden in the volcano’s vent

12. What Erupts from a Volcano? Pyroclastic material Rock fragments created by eruptions. Magma explodes from volcano and solidifies in the air. Existing rock is shattered by powerful eruptions. Pyroclastic flows are the most dangerous type of eruption because they are very hot and travel very fast. Volcanic blocks Volcanic bombs Volcanic ash

13. Types of Lava Flows Lava flows are superheated streams of molten rock that flow at 1 – 50 mph. Pyroclastic flows are avalanches of hot ash, rock fragments, and gases that flow at speeds greater than 100 mph. Landslides are avalanches of rock, snow and ice on slopes of volcanoes (loosened and tumbling due to seismic activity). Lahars (mud flows) are a mixture of volcanic ash and water (like wet concrete)

14. How do volcanoes affect the Earth? Flows and Fallouts hot ash can flow really quickly Knock down buildings Dam rivers (flooding/drought) Kill crops and livestock Climatic Changes Ash & Gases can block sunlight Drop average global temperature noticeably

15. Types of Volcanoes Shield volcano Cinder cone volcano Composite volcano On the chart in your notes, draw a sketch of each volcano, and describe what it looks like in the top row!

16. Shield Volcano Shield volcanoes are broad, gently sloping volcanic mountains (What does it look like?) Shield volcanoes are slowly formed by layer over layer of solidified lava, and formed by effusive eruptions of fluid lava. (How is it formed?) Shield Volcanoes have effusive eruptions that are low in silica –flows easily and spreads out in thin layers (Describe the eruption)

17. Shield Volcano Example: Mauna, Loa Takes up much of the Hawaiian Island 2 ½ miles, 13,678 ft. high

18. Composite Volcano Composite volcanoes are formed from both explosive and effusive eruptions, and are built from layers of lava and rock fragments. (How does it form?) Composite volcanoes have very violent eruptions with viscous lava flows & layers of tephra, or rock fragments (Describe the eruption)

19. Composite Volcano Example: Mt. Saint Helens, Washington

20. Cinder Cone Volcano Cinder cones are the smallest volcanoes (< 500 ft), formed by explosive eruptions of explosive lava, and can form near other volcanoes (How does it form?) Blown violently into the air, the erupting lava breaks apart into fragments called cinders that fall and accumulate around the vent. (Describe the eruption) Cinder cones are easily eroded. They have short life spans as gas causing violent eruptions is quickly depleted.

21. Cinder Cone Volcano Example: Paricutin, Mexico

22. Measuring Small Quakes –Before eruption, increase in number & intensity Measuring Slope –Bulges may form with magma (tiltmeter) Measuring Volcanic Gases –Outflow of volcanic gases Sulfur dioxide, carbon dioxide Measuring Temperature from Orbit –Measure changes in temperature over time How do volcanologists predict eruptions?