1. Chapter 7 Section 2
Volcanic Eruptions

2. Types Of Lava
Lavas can be grouped by the different kinds of rocks they produce, generally based on the amounts of iron, magnesium, and silica.

3. How can Volcanoes be classified?

4. Volcanoes can be grouped by the different kinds of rocks they produce.

5. Because of this large variation:
Silica content is used to classify rocks.

6. The type of rock produced depends on chemical composition.

7. When geologists analyzed numerous types of volcanic rocks from around the world, they found that the silica (SiO2) content varied by as much as 40 weight percent.

8. Classification system bases on appearance

9. A simple classification scheme based on silica content is used.

10. Mafic Lava Dark colored rich in magnesium and iron
usually of oceanic crust origin
Basalt - low SiO2=less than 52%

11. Mafic Lava Flows
Classified on appearance.

12. Pahoehoe lava
smooth, runny, high temperature lava with a ropy appearance

13. aa lava
rough jagged lava that forms from thicker non-runny lava

14. Blocky flow
large angular pieces which flow like a slow motion avalanche

15. Pillow lava
forms when mafic lava cools underwater

16. Felsic Lava High silica content - lesser amounts of iron and magnesium
lighter color
usually formed from continental crust
Rhyolite

17. Intermediate Lavas
Have a range of compositions that fall between the mafic and the felsic varieties

18. Too Summarize…

19. Kinds of Eruptions

20. Quiet Oceanic volcanoes mafic lava gases can easily escape
flow like a red-hot river

21. Explosive Continental volcanoes felsic lavas
large amounts of trapped gases
eruptions send molten and solid particles shooting into the air

22. ERUPTIVE PRODUCTS

23. Tephra (Pyroclastic Material)
rock fragments of various sizes that are blown into the air, generally from felsic lava because of rapidly expanding gases.

24. Volcanic Dust
Tephra particles less than 0.25 mm in diameter.

25. ash
fine dust less than 2 mm in diameter

26. lapilli - little stones (cinders)
particles up to 64 mm in diameter

27. bombs
chunks of red-hot rock which cool as they fly through the air

28. volcanic blocks
Formed from solid rock blasted from the fissure

29. pumice
light weight rock
formed from air passing through it

30. Lava flows molten rock that reaches the surface
depends upon temperature and chemical composition

31. Pyroclastic flow
Turbulent mixture of hot gas and rock fragments that moves like liquid / very fast

32. TYPES OF VOLCANOES
shape classification

33. Cinder cone made entirely from tephera small with steep sides
short-lived (less than 1000 years)
not very explosive

35. Shield Volcano quite large and form from very fluid lava
rarely explosive
gently sloping sides
are made of basaltic lava

36. Puu Oo Vent, Hawaii Crater
Funnel-shaped pit at the top of a volcanic vent

37. Types of Volcanoes (classified by shape)
Shield volcano: characteristic of eruptions emitting low viscosity lava. Hawaii is an example.
Olympus Mons is the largest volcano on Mars. This shield volcano, similar to volcanoes in Hawaii, measures 624 km (374 mi) in diameter by 25 km (16 mi) high. It is 100 times larger than Mauna Loa on Earth. Located on the Tharsis Plateau near the equator, Olympus Mons is bordered by an escarpment. The caldera in the center is 80 km (50 mi) wide and contains multiple circular, overlapping collapse craters created by different volcanic events. The radial features on the slopes of the volcano were formed by overflowing lava and debris.

38. Stratovolcano (composite)
a succession of alternating lava flows and tephra deposits
usually thick lava and are some what explosive
made mostly of andesite (Mt. Rainier)

39. Mount Rainier

40. Mount Saint Helens

41. Lava Dome
a single mass of extruded lava that’s too thick to move away from the volcano
very explosive (Mt. St. Helens)

42. Craters and Calderas

43. Caldera
Large basin-shaped depression formed when an explosion destroys the upper part of a volcanic cone

44. Crater Lake
(1,932 feet deep). The lake was formed by the explosion and collapse of 12,000 foot Mt. Mazama

45. Wizard Island – regrowing volcano
Crater Lake
Wizard Island – regrowing volcano

46. Can Be Quite Large
This happens when the magma chamber empties and the roof collapses.

47. Yellowstone