Welcome to my 7th grade science blog!

Friday, January 28, 2011

Chapter 2 Section 1 Full Notes


  • Movement of tectonic plates creates forces that are stress
  • Stress is a force that acts on rock to change its shape or volume.
  • Since stress is force, it is stored in rock as energy until it is released when the rock breaks or changes shape.
  • Tension - Stretching rock
  • Compression - Pushing rock together
  • Shearing - masses of rock slipping
  • Tension, compression, and shearing work over millions of year to change the shape and volume of rock.
  • Some rocks are brittle and snap, some bend slowly.
  • Types of forces:
  • Tension pulls on the rust and stretches and makes rocks thinner. It happens when two plates are moving apart.
  • Compression squeezes rock until it folds or breaks. Often compresses rock.
  • Shearing is when stress pushes rock into different directions, while rubbing against each other.

  • When stress build up in a rock or the tectonic plates, the rock breaks and a fault is created.
  • Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust breaks. There are three main types of faults: normal faults, reverse faults and strike-slip faults.
  • Normal Faults: tension in earth crust pulls rock apart, tearing rock and creating a normal fault. In all Normal Faults, the fault is at an angle so there is a part mostly on top, and a port mostly on the bottom, like so:
__


                      \____

                  • The part mostly above is the hanging wall, and the bottom one is the footwall.
                  • Reverse Faults: Caused when rock of crust is pushed together. Has same structure as normal fault, but movement is in opposite direction, which means the hanging wall moves over the footwall.
                  • Strike-Slip Faults: created by shearing when plates move past each other. Rocks on each side of the fault slip past eachether pretty much side to side, with no up and down motion. A SS Fault that is boundary between two plates is a transform boundary.
                  Changing Earth's Surface
                    • Over millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines and synclines, folded mountains. fault-block mountains and plateaus.
                    • Plate movement can cause crust to fold.
                    • Folds: Folds are bends in rock that form when compression shortens and thickens part of Earth's crust. Can be tiny or huge.
                    • Anticline: fold in rock that bends upward.
                    • Syncline: Fold that bends downward.
                    • Folding produced some of largest mountain ranges, like Himalayas.
                    Later - From Class
                      • Convergent boundary = compression. Can cause mountains, volcanoes, subduction
                      • Divergent Boundaries = Tension

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