1. Volcanic Activity

2. Silica  Earth’s crust and mantle are mostly made of silica The more silica in the magma, the thicker it is

3. Silica Magma with a lot of silica makes light-colored lava that is very thick When high silica lava cools, it makes rocks like rhyolite, pumice and obsidian

4. Silica Magma that does not have much silica moves quickly and is thin. Low silica magma is dark colored and makes rocks like basalt

5. Types of Volcanic Eruptions The amount of silica determines if an eruption is quiet or explosive

6. Quiet Eruptions Quiet eruptions are when magma flows out easily from the vent and volcano sides. Quiet eruptions produce two types of lava

7. Quiet Eruptions Two types of lava Pahoehoe is fast- moving, hot, thin lava

8. Quiet Eruptions Aa lava is cooler and slower moving. It hardens to form rough, jagged rocks.

9. Explosive Eruptions If magma is thick, the eruption is explosive. The magma builds up and plugs the pipe, building pressure. The erupting gases push the magma out quickly.

10. Explosive Eruptions The force of the explosion splits the lava into several pieces. Ash are smallest pieces Cinder are pebble-sized particles.

11. Explosive Eruptions Bombs are larger pieces (baseball to car)

12. Explosive Eruptions Pyroclastic flow is when an eruption spews out ash, cinders, bombs, and gases.

13. Stages of a Volcano There are three stages of a volcano Active: The volcano is erupting or may erupt in near future Dormant: The volcano is sleeping and may awake in the future.

14. Stages of a Volcano Extinct: The volcano is unlikely to erupt again.

15. Other Types of Volcanic Activity Hot springs form when water around the volcano is heated by magma. Geysers are created when this hot water gets trapped under ground and builds pressure until it erupts.

16. GEYSER

17. Geothermal Energy Geothermal energy uses water heated naturally by magma to create energy. Steam spins the turbines which turns a generator to make electricity.

18. Monitoring Volcanoes We are getting better at predicting volcanoes. Many small earthquakes around a volcano are common before an eruption.

19. Volcano Hazards People are dormant volcanoes can be caught by surprise. Quiet eruptions are dangerous because the lava sets fire to everything.

20. Volcano Hazards Explosive eruptions are dangerous because of volcanic gases as well as flying lava. Eruptions can cause landslides and avalanches.