1. Volcanoes

2. What is a volcano?
A mountain that forms when magma reaches the Earth’s surface through cracks in the crust called vents.

3. What is a nonexplosive volcanic eruption?
Relatively calm outpourings of lava flow out onto Earth’s surface. Example: Mount Kilauea, Hawaii.

4. What is an explosive volcanic eruption?
Clouds of hot debris and gases shoot out from the volcano. Instead of producing lava, molten rock is blown into millions of pieces that harden in the air. Example: Mount St. Helens, Washington State.

5. What determines whether an eruption will be explosive or nonexplosive?
The composition of the magma involved.
Water – Magma with high water content will erupt explosively. Effect similar to carbonation in soda pop.
Silica – Magma with a high percentage of silica is thicker, and flows slowly. It’s more likely to cool in and plug up a vent resulting in built up pressure.

6. What is pyroclastic material?
Rock fragments created by magma that cools in the air from explosive eruptions.
Volcanic blocks – largest, consist of solid rock blasted from volcano
Volcanic bombs – large blobs of cooled magma
Lapilli – pebble-like bits of cooled magma
Volcanic ash – forms when gases in stiff magma expand rapidly and walls of the gas bubbles explode into tiny glasslike slivers

7. What is pyroclastic material?
Volcanic Blocks
Volcanic bombs
Volcanic Ash
Lapilli

8. What are the different types of lava?
Blocky lava – cool, stiff lava that cannot travel far from the erupting vent.
Pahoehoe – lava flows slowly forming a glassy surface with rounded wrinkles
Aa – slightly stiff lava that pours out quickly and forms a brittle, jagged crust
Pillow lava – forms when lava erupts underwater; looks like rounded lumps

9. Types of Lava
Pillow Lava
Pahoehoe

10. Types of Lava
Blocky Lava Aa

11. What are the different types of volcanoes?
Shield volcanoes – built out of layers of lava from repeated nonexplosive eruptions; has gently sloping sides, but can be enormous. Example: Mauna Kea which is an underwater volcano taller than Mount Everest
Cinder cone volcanoes – small volcanic cones made entirely of pyroclastic material; has steep slopes with a narrow base. Example: Mount Paricutin, Mexico

12. What are the different types of volcanoes? (continued)
Composite volcanoes – most common type; formed from explosive eruptions of pyroclastic material, followed by quieter outpourings of lava. Forms alternating layers of pyroclastic material and lava. Have a broad base and get steeper near the summit. Example: Mount Fuji, Japan

13. Shield Volcano
Mauna Kea

14. Cinder Cone Volcano
Mt. Etna, Italy

15. Composite Volcano
Mt. Fuji, Japan

16. What is the “Ring of Fire”?
Boundary of the tectonic plate surrounding the Pacific Ocean where about 75% of Earth’s active land volcanoes are located.

17. Ring of Fire