1. Volcanic Activity Earth Science Ch. 18

3. Factors affecting magma formation ► Pressure ► Temperature ► Water-causes rock to melt at a lower temp ► YouTube - Volcano Eruptions YouTube - Volcano Eruptions YouTube - Volcano Eruptions

4. Map of volcanoes Fig. 18-2

5. Viscosity-resistance to flow ► Honey has a high viscosity ► Water has a low viscosity

6. ► The hotter the magma, the lower the viscosity ► YouTube - Ol Doinyo Lengai Volcano YouTube - Ol Doinyo Lengai Volcano YouTube - Ol Doinyo Lengai Volcano

7. ► Magma=below surface ► Lava=above surface ► Vent-what lava erupts through ► Crater-depression around the vent ► Caldera-collapsed volcano

8. Caldera (in AK)

9. Crater Lake, OR (caldera)

10. Types of Volcanoes ► 1. Shield Volcanoes  -broad slope  -largest type of volcano  -usually nonexplosive eruptions  Ex. Hawaiian Islands ► Fig. 18-12

12. Hawaii

13. Cinder-cone volcanoes ► Smallest type of volcano ► Less than 500m ► More viscous magma, lots of gases, so it makes it very explosive

15. Cinder cone antomy

16. Composite volcanoes ► Layers of ash/volcanic fragments and lava ► Violent eruptions ► Ex. Mt St. Helens and Mt. Rainier in USA

17. layers

19. ► Cinder cones=smallest; steepest slopes ► Shield=largest ► volcanic eruption - Google Video volcanic eruption - Google Video volcanic eruption - Google Video ► HowStuffWorks Videos "Mt. Saint Helens' Powerful Erruption" HowStuffWorks Videos "Mt. Saint Helens' Powerful Erruption" HowStuffWorks Videos "Mt. Saint Helens' Powerful Erruption"

21. Mt. St. Helens

22. Tephra ► Fragments thrown in air from eruption ► Pyroclastic flows- clouds of ash, gas, and tephra down slope up to 150 mph. Temp can exceed 700 C.

23. Distribution of volcanoes is not random ► Found along plate boundaries (Ring of Fire), mid-ocean ridges ► Fig. 18-16 ► Some found at hot spots, where plumes of mantle (magma) rise up-ex. Hawaii ► Fig. 18-17

25. The End