1. Volcanoes

2. Magma: liquid, molten rock underground
Lava: magma that reaches the surface

3. The composition of lava depends on dissolved gases and silica content

5. Dissolved Gases
Example: water vapor, carbon dioxide (CO2), sulfur (S)
*More gas = more explosive eruption

6. Silica Content
More silica (SiO2) = thick magma
Viscosity- ability to resist flow.
High viscosity = thick flow
Low viscosity = thin flow

7. Two classifications of lava:
1) Felsic: much silica, light-colored, slow moving (continental crust)

8. 2) Mafic: low silica and gas, dark-colored, fast moving (oceanic crust)

9. 3 types of mafic lava:
1) Aa Lava=
choppy
2) Pahoehoe
= ropy

10. 3) Pillow Lava= underwater

11. Hardened Lava
In Hawaii

12. Volcano: place where magma reaches the surface
Volcanism: when a fissure or crack develops in the crust allowing magma to reach the surface

14. Pahoehoe

15. HOT SPOTS: areas of volcanic activity in the middle of lithospheric plates

16. Hawaiian Islands

17. Volcano Anatomy
Vent: opening from which lava flows
Crater: funnel-shaped pit or depression at top of volcano
Caldera: depression where the walls have collapsed

19. Volcanic vents turn into plugs when the lava cools

20. Diamond Head Crater in Hawaii

21. Pyroclastic Material (tephra):solid particles produced in eruptions
Ash (<2mm)
Lapilli (<64mm)
Bombs
Blocks

22. ash

24. lapilli

25. bombs

26. blocks

27. Types of volcanoes…

28. composed of calm lava flows form gently sloping, dome- shaped mountain
1.Shield Volcano
composed of calm lava flows
form gently sloping, dome- shaped mountain
basaltic (mafic) magma

29. Example:
largest = Mauna Loa in Hawaii

30. Made mostly of tephra and other rock particles
2. Cinder Cone Volcano
Made mostly of tephra and other rock particles
Formed from explosive eruptions
small, narrow base & steep sides
Grantic (felsic) magma

32. Symmetrical build up of alternating layers of rock and lava
3. Composite Volcano
(Stratovolcano)
Symmetrical build up of alternating layers of rock and lava
highly explosive eruptions with high silica and high gas content
forms large, cone-shaped mountains

33. Composite example 1
Mt. St. Helens- before

34. Mt. St. Helens- after

35. Ex. 2 -Mount Vesuvius - Pompeii
20 feet of
volcanic ash
smothered
The city!

36. Mount Vesuvius – Pompeii= composite
20 feet of
volcanic ash
smothered
The city!