Bahan ajar Geologi Dasar Fakultas Teknologi Mineral UPN "Veteran" Yogyakarta

1. Module 12
Volcanoes

2. The gods of volcanoes doing their task

3. VOLCANOES
 A volcano is a vent or fissure in the Earth’s crust
through which molten magma, hot gases, and
other fluids escape to the surface of the land or to
the bottom of the sea
 Volcanoes may be classified broadly into:
 Central Types: the products escape via a single
pipe (vent)
 Fissure Types: the products escape from a
linear vent or crack

4. Vent positions

5. Vent positions
Central Eruption
Fissure Eruption
Side Eruption

6. Earth’s Geotherm
 GEOTHERM: increase in
temperature with depth in the
earth
 GEOTHERMAL GRADIENT is
the rate of change of T with
depth
 In upper 100 km, average
geothermal gradient = 300C
km-1
 Heat source is decay of
radioactive elements
 This heat causes melting of
rocks to form Magma

7. Composition of Magma
 Variation in magma properties include:
 SILICA CONTENT
varies from 45% to 75%
 VOLATILES (GAS CONTENT)
most common gases: H2O vapor,
CO2, SO2, H2S
 TEMPERATURE OF ERUPTED MAGMA
varies from 12000C to about 8000C
 Variation in magma properties affect VISCOSITY of
the magma

8. Viscosity of Magma
 VISCOSITY refers to the thickness or fluidity of a
liquid
 Liquid with HIGH viscosity are very thick,
sticky
 Liquid with LOW viscosity are very fluid
 Effect of various properties on magma viscosity:
 Temperature: HIGH temperature = LOW
viscosity (i.e. very fluid)
 Silica Content: HIGH silica = HIGH viscosity
 Volatile Content: HIGH volatiles = LOW
viscosity
(However, high gas contents contribute to
explosive eruptions)

9. Types of Volcanoes

10. Types of Volcanoes

11. Shield Volcanoes

12. Shield Volcanoes

13. Shield Volcanoes

14. Shield Volcanoes

15. Shield Volcanoes

16. Shield Volcanoes

17. Shield Volcanoes
HOT SPOT

18. Cinder Cone Volcanoes

20. Cinder Cone Volcanoes

21. Strato Volcanoes

22. Strato Volcanoes

23. Strato Volcanoes

24. Strato Volcanoes

25. Strato Volcanoes

26. Strato Volcanoes

27. Lava Dome Volcanoes

28. Dome Volcanoes

29. Caldera Volcanoes

30. Caldera Volcanoes
The formation of
Caldera

31. Eruption Types

32. Eruption Types
HAWAIIAN-HAWAI

33. Eruption Types
STROMBOLIAN - ANAK KRAKATAU

34. Eruption Types
VULCANIAN DOME - MERAPI

35. Eruption Types
VULCANIAN - SURTSEYAN

36. Eruption Types
VULCANIAN - PAPANDAYAN
GAMALAMA

37. Eruption Types
PELEEAN - ST HELLENS

38. Eruption Types
PLINIAN PINATUBO

39. Eruption Types
PLINIAN - TAMBORA

40. Global Distribution of Volcanoes

41. from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270
Distribution of Volcanoes
Most subduction zones are in the “Ring of Fire” (so-called
because of volcanism of the Pacific)

42. Volcanism & Plate Tectonics
Volcanism in continental
Volcanism in islands arc

43. Volcanism & Plate Tectonics
Volcanism in
Mid Oceanic Ridge
Pacific Ocean

44. Volcanism & Plate Tectonics
Hot Spot Volcanism

45. Classification of Volcanic Environment

46. Types and Zones of Volcanism

47. Finally . . .
Rest in Peace
COLUMNAR JOINT
VOLCANIC NECK

48. Major Volcanoes of Indonesia
(with eruptions since 1900 A.D.)

49. Distribution of Magmatic Arcs of Indonesia
(source: Carlile & Michell, 1994)