1. Volcanic Eruptions
Chapter 7.2

2. Volcanic Eruptions
Through analysis of the chemical composition of volcanic rock, geologists have concluded that there are two general types of lava.
Mafic lava
Dark colored when hardened.

3. Mafic Lava Rich in magnesium and iron.
Forms much of the oceanic crust.
Tends to quietly flow.

4. Mafic Lava

5. Felsic Lava Felsic lava
High in silica with lesser amounts of magnesium and iron.
Lighter color when it hardens.
Common in the continental crust.
Tends to be explosive.

6. Felsic Lava

7. Pahoehoe Pahoehoe (puh-hoy-hoy)
When mafic lava cools rapidly, the surface of the flow forms a crust that is wrinkled by movement. This is solidified mafic lava with a wrinkled surface.
Pahoehoe means “ropy” in Hawaiian.

8. Pahoehoe

9. AA
AA (ah-ah)
Lava that is deformed rapidly or grows too thick to form wrinkles, and the surface breaks into jagged chunks. Jagged chunks of lava formed by rapid cooling on the surface of a lava flow.
AA refers to the sharp, blocky texture of the volcanic rock.

10. AA

11. Lava Tubes
Lava Tubes
These tubes are created when the outer part of the mafic lava flow cools rapidly and forms a hardened shell around a liquid interior which flows out leaving the hardened shell.

12. Lava Tube

13. Pillow Lava Pillow Lava
This is when lava flows out of fissures on the ocean floor, cools rapidly, and separated into rounded blobs.

14. Pillow Lava

15. Volcanic Rock Fragments
Pyroclastic materials are thrown into the air when felsic lava explodes.
Pyroclastic materials are rock fragments ejected from a volcano.
Volcanic ash is pyroclastic material less than 2mm in diameter.
Volcanic dust is material less than .25mm in diameter.

16. Volcanic Rock Fragments

17. Volcanic Rock Fragments
Lapilli (luh-pil-ie) is material that is less than 64mm in diameter.
Means “little stones” in Latin.
Volcanic bombs are large, spindle shaped clots of lava thrown out of the volcano.
Volcanic blocks are the largest possible pyroclastic material that is formed from solid rock blasted from a volcanic fissure.

18. Bombs & Blocks

19. Volcanic Cones
Volcanic cones are piles of ejected material that build up around the vent and there are three main types.
Shield volcanos are broad at the base and have gently sloping sides.
These types of volcanos cover a large area.

20. Shield Volcano

21. Volcanic Cones
Cinder cones are made of solid fragments ejected from the volcano, are very steep, and are rarely more than a few hundred meters high.
Composite or Stratovolcano is a steep sloped volcanic material deposited with alternating layers of hardened lava flows and pyroclastic materials.

22. Cinder Cone

23. Stratovolcano

24. Craters & Calderas Craters & Calderas
A crater is a funnel shaped pit at the top of a volcanic vent.
Craters are formed when material is blown out of the volcano by explosion.
A caldera forms when the magma chamber below a volcano is emptied and the volcano collapses leaving a large basin shaped depression.

25. Crater

26. Caldera

27. Label