1. Ch. 6 Volcanoes

2. Volcanoes
A volcano is a weak spot in the crust where magma comes to the surface
Magma is molten rock, gases, and water from the mantle
Magma becomes lava when it comes to the surface
Lava cools to become igneous rock

3. Types of Rock
Igneous- molten material, such as lava or magma, cools and hardens
Slow cooling- large crystals (granite)
Fast cooling- small crystals (basalt)
Metamorphic- great heat and pressure changes minerals or other rock
Heat and pressure increases inside the Earth

4. Types of Rock Sedimentary- sediment squeezed and glued together
Sediment- small pieces of rock or fossils that have been broken down by erosion or weathering

5. The Rock Cycle
The rock cycle slowly builds, destroys, and changes rock
Continuous and many pathways

6. The Rock Cycle

7. Volcanoes and Plate Tectonics
Volcanic belts are found at plate boundaries, such as the Ring of Fire around the Pacific Plate

8. Volcanoes and Plate Tectonics
Divergent boundaries- magma comes out of rift valleys to build mountains
Convergent boundaries
Oceanic plate sinks
Rock on top melts and becomes magma
Magma erupts and becomes lava

9. Volcanoes at Plate Boundaries

10. Hot Spots
Hot spots- volcanoes that form when magma erupts through crust to get to the surface
Hawaii
Yellowstone National Park

11. Parts of a Volcano Magma chamber-collects magma
Pipe- tube that connects magma chamber to surface
Vent- opening on the Earth’s crust

12. Parts of a Volcano Lava flow- area covered by lava
Crater- bowl-shaped area around a volcano’s central vent
Caldera- large circular depression formed when magma chamber empties and the roof collapses

13. Eruptions Pressure and gases force magma out of a volcano
Silica makes magma thick and sticky
Types of eruptions
Quiet eruptions- lava oozes to surface
Thin, runny lava that is low in silica
Hawaiian Islands
Examples are pahoehoe and aa

14. Eruptions Types of eruptions
Explosive eruptions- thick and sticky lava which traps water
Water makes eruptions more explosive
Produces pyroclastic material
Magma that erupts as fragments of molten material and solidifies in the air
Pieces of volcano that breaks off
Mt. St. Helens in 1980

15. Life Cycle Geologists determine how likely a volcano will erupt again
Stages
Active- erupting or will erupt in the near future
Mt. Shasta and Lassen Peak
Dormant- “sleeping,” but can become active again
Long Valley in eastern Sierras
Extinct- unlikely to erupt again
Diamond Head in Honolulu

16. Volcanic Landforms Made of lava, ash, and other materials
Types of Volcanoes
Shield Volcano- made from nonexplosive eruptions
Low in silica
Wide with gentle slopes
Cinder Cone- made from explosive eruptions
High in silica
Steep, cone-shaped, found in clusters

17. Volcanic Landforms Types of Volcanoes
Composite- alternating layers of pyroclastic material and lava flow
Also known as stratovolcano
Most common

18. Volcanic Landforms
Lava Plateaus- lava flows out of long cracks called fissures
Thin, runny lava flows far before cooling

19. Shield Volcano- Medicine Lake, CA

20. Cinder Cone Volcano- Mt. Bromo, Indonesia

21. Composite Volcano- Mt. Shasta, CA

22. Lava Plateau- Modoc Plateau, CA

23. Magma Landforms
Formed when magma goes into cracks, but does not come to surface
Magma cools underground
Erosion exposes harden magma

24. Magma Landforms Types Volcanic Necks- magma hardens in pipe
Dikes and sills- magma cools between rock layers
Igneous intrusions
Sill are horizontal
Dikes cross rock layers
Batholiths- massive rock forms when large body of magma cools

25. Magma Landforms