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Lesson 5 in Earth and Life Science-Types of Stress and Fault.pptx
- 1. Forces in the Earths Crust
- 2. Objective Describe how rocks behave under different types of stress
- 3. Stress-A force that acts on rock causing a change in its shape or volume.
- 4. There are 3 kinds of stress that occur in the crust Compression Tension Shearing
- 6. Compression Squeezes rock until it folds or breaks. - a squeezing force
- 7. Compression is common in convergent tectonic plate boundaries, where two plates collide
- 8. Compression stress can cause folding, faulting, and mountain- building processes
- 9. Tension Pulls on the crust, stretching rock so that it becomes thinner in the middle. -Occurs where two plates are moving apart. - a stretching force
- 10. This type of stress occurs in divergent plate boundaries, where plates move away from each other. Tensional stress can lead to the formation of rift valleys and normal faults.
- 11. Shearing - occurs when forces act parallel to each other but in opposite
- 12. Pushes a mass of rock in two opposite direction. Shearing can cause rock to break and slip apart or to change its shape. - a ripping force
- 14. When enough stress builds up in rock, the rock breaks, creating a fault. A fault is a break in the crust where rock surfaces slip past each other. The rocks on both sides of a fault can move up or down, or even sideways.
- 15. Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust breaks, but faults can also occur almost anywhere.
- 16. There are three main types of faults: normal faults, reverse faults, and strike-slip faults.
- 17. Normal Faults -it occurs when rock in the Earths crust is pulled apart The fault is at an angle, so one block of rock lies above the fault (foot wall), while the other block lies below the fault (hanging wall). Normal faults occur where plates diverge, or pull apart.
- 19. Reverse Faults In places where the rock of the crust is pushed together, compression causes reverse faults to form. Has the same structure as a normal fault, but the blocks move in the opposite direction.
- 20. As in a normal fault, one side of a reverse fault lies at an angle above the other side. The hanging wall of a reverse fault slides up over the footwall.
- 22. Strike-Slip Faults Plates move past each other, -shearing creates strike-slip faults The rocks on either side of the fault slip past each other sideways, with little up or down motion.
- 24. PLATE BOUNDARIES
- 25. What are the three types of boundaries? Divergent Boundaries Convergent Boundaries Transform Boundaries
- 26. Divergent Boundaries A plate boundary where two plates move away from each other. RIFTING causes SEAFLOOR SPREADING
- 27. How is the rock pulled at Divergent Boundaries? Rock gets THIN in the middle as it is pulled apart. The STRESS involved here is tension
- 28. Features of Divergent Boundaries Mid-ocean ridges rift valleys fissure volcanoes
- 30. A plate boundary where two plates move towards each other. Boundaries between two plates that are colliding The stress involved here is COMPRESSION CONVERGENT BOUNDARIES
- 31. Andes Mountains, South America
- 32. May form Mountain Ranges. These are Folded Mountains, like the Himalayas
- 33. Transform Boundaries A plate boundary where two plates move past each other in opposite direction.
- 34. What happens at Transform Boundaries? May cause Earthquakes when the rock snaps from the pressure. A famous fault @ a Transform Boundary is the San Andreas Fault in California.
- 35. San Andreas Fault, CA
- 36. Uplifting Earths Crust The forces that raise mountains can also uplift or raise plateaus. A plateau is a large area of flat land elevated high above sea level. Some plateaus form when forces in the Earths crust push up a large, flat block of rock. Like a fancy sandwich, a plateau consists of many different flat layers, and is wider than it is tall.
- 38. What forces can create plateaus? The formation of plateaus is primarily associated with compressional stress and, in some cases, tensional stress or uplift forces.
- 39. Compressional Stress When tectonic plates collide, the resulting compressional forces can cause layers of the Earth's crust to fold and uplift, leading to the formation of plateaus. This often occurs in areas near or at convergent plate boundaries, where the crust is squeezed and thickened. Example: The Tibetan Plateau, formed by the collision of the Indian and Eurasian plates.
- 41. Uplift from Mantle Dynamics Plateaus can also form due to broad uplift caused by mantle upwelling, where heated material from the Earth's mantle rises toward the crust, pushing it upward without significant horizontal compression. This is known as isostatic uplift. Example: The Colorado Plateau, which was uplifted due to forces related to mantle convection and buoyancy
- 43. Tensional Stress In areas of rifting, where tectonic plates are pulling apart (divergent boundaries), the thinning of the crust can sometimes create broad elevated regions. These regions can later erode to form plateaus. Example: The East African Rift, where tensional forces are pulling the region apart, leading to the uplift of certain areas.
- 45. GET READY FOR A SHORT QUIZ
- 46. 1. ROCKS UNDER COMPRESSIONAL FORCE ARE a. pushed apart b. transformed c. diverged d. crushed
- 47. 2. ROCKS UNDER TENSIONAL FORCE ARE a. pushed towards each other b. compressed c. pulled apart d. squeezed
- 48. 3. FAULTING OCCURS DUE TO a. one force only b. two forces c. three d. four forces
- 49. 4. NORMAL FAULT IS CAUSED BY a. tension b. compression c. expansion d. collision
- 50. 5. ROCKS UNDER TENSIONAL FORCE ARE a. pushed towards each other b. compressed c. expanded d. pulled apart
- 51. 6. CONVERSELY, A RIFT VALLEY CAN BE FORMED BY a. tensional force b. compressional force c. expansion force d. contact force
- 52. 7. WHAT TYPE OF FORCE IS INVOLVED IN THE FORMATION OF TRANSFORM FAULT? a. compressional force b. shearing force c. tensional force d. extension
- 53. 8.(Picture A) 9.(Picture B) 10.(Picture C) Name what type of plate boundaries are the ff. :