1. Plates

2. A section of the lithosphere that slowly moves, carrying pieces of continental and oceanic crust.

3. Pangaea

4. The name of the single land mass that broke apart 225 years ago and gave rise to today’s continents.

5. Plate Tectonics

6. The theory that states that Earth’s plates are in constant, slow motion.

7. Plate Boundaries

8. A crack in the lithosphere where two of Earth’s plates meet.

9. Earthquake

10. The shaking that results from the movement of rock beneath Earth’s surface.

11. Stress

12. A force that acts on a rock to change its shape for volume.

13. Shearing

14. Stress that pushes a mass of rock in opposite direction.

15. Tension

16. Stress that stretches rock so that it becomes thinner in the middle.

17. Compression

18. Stress that squeezes rock until it folds or breaks.

19. Fault

20. A break or crack in Earth’s lithosphere along which rocks move.

21. Strike-slip fault

22. A type of fault where the rocks on either side move past each other sideways with little up-or-down motion.

23. Normal fault

24. A type of fault where the hanging wall slides downward; caused by tension in the crust.

25. Hanging wall

26. The block of rock that forms the upper half of a fault.

27. Footwall

28. The block of rock that forms the lower half of a fault.

29. Reverse fault

30. A type of fault where the hanging wall slides upward; caused by compression in the crust.

31. Fold

32. A bend in rock that forms where part of the Earth’s crust is compressed.

33. Plateau

34. A landform that has a more or less level surface and is elevated high above sea level.

35. Anticline

36. A fold that bends upward into an arch.

37. Syncline

38. A fold in rock that bends downward in the middle to form a bowl.

39. Magma chamber

40. The pocket beneath a volcano where magma collects.

41. Pipe

42. A long tube through which magma moves from the magma chamber to Earth’s surface.

43. Vent

44. An opening through which molten rock and gas leave a volcano.

45. Lava flow

46. The area covered by lava as it pours out of a volcano’s vent.

47. Crater

48. A bowl-shaped area that forms around a volcano’s central opening.

49. Silica

50. A material that is formed from the elements oxygen and silicon; silica is found in magma.

51. Pahoehoe

52. A hot, fast-moving type of lava that hardens to form smooth, ropelike coils.

53. Aa

54. A slow-moving type of lava that hardens to form rough chunks; cooler than pahoehoe.

55. Pyroclastic flow

56. The expulsion of ash, cinders, bombs, and gases during an explosive volcanic eruption.

57. Active

58. A volcano that is erupting or shows signs of eruption in the near future.

59. Dormant

60. A volcano that does not show signs of erupting in the near future.

61. Extinct

62. A volcano that is unlikely to erupt again.

63. Geyser

64. A type of hot springs that builds up pressure underground an erupts at regular intervals as a fountain of water and steam.

65. Geothermal energy

66. Heat energy in Earth’s interior from water or steam that has been heated by magma.