Volcanoes

1. Volcanoes Chapter 13

2. Magma • Liquid rock produced under Earth’s surface

3. Volcanism • Any activity that includes the movement of magma toward or onto Earth’s surface.

4. Lava • Magma that flows onto Earth’s surface; the rock that forms when lava cools and solidifies

5. volcano • A vent of fissure in Earth’s surface through which magma and gases are expelled

6. Hot Spot • A volcanically active area of Earth’s surface, commonly far from a tectonic plate boundary

7. Mafic • Describes magma or igneous rock that is rich in magnesium and iron and that is generally dark in color

8. Felsic • Describes magma or igneous rock that is rich in feldspar and silica and that is generally light in color.

9. Pyroclastic material • Fragments of rock that form during a volcanic eruption including volcanic ash, dust, blocks, bombs and lapilli

10. Caldera • A large, circular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink

11. Areas of Volcanoes Boundaries of tectonic plates Subduction zones Mid-ocean ridges

12. Pillow Lava When an underwater volcano erupts at a mid-ocean ridge, the magma cools quickly pillow lava forms

13. Subduction Zone A trench will form on the ocean floor when one plate subducts under another plate. When an oceanic crusts subducts under another oceanic crust and island arc forms

14. Pahoehoe & Aa • When lava cools rapidly and • the flow the continues the crust wrinkles and forms a ropy volcanic rock known as pahoehoe. • The surface breaks into jagged chunks known as aa

15. Volcanic Eruptions When the temperature of rock rises above its meling point magma will form Volcanic eruptions may be signaled by a change in earthquake activity Mount St. Helen experienced an explosive eruption

16. Pluton Igneous rock formations created when magma does not reach Earth’s surface, but cools and solidifies inside the crust