ROCK BEHAVIORS UNDER STRESS

• Deformation


  Changes in the shape, location, size, tilt or break of rocks and large masses due to squeezing or shearing
• Stress


  The force per unit area that is placed on a rock
• Types of Stress


  • Tensional stress
  • Compressional stress
  • Shear stress
• Tensional stress


  Causes rocks to be pulled apart, resulting in lengthening and breaking apart. Found at divergent plate boundaries.
• Compressional stress


  Causes rocks to fold or fracture by squeezing them together. Found at convergent plate boundaries.
• Shear stress


  Happens when forces slide past each other in opposite directions, resulting in slippage and translation. Found in transform plate boundaries.
• Folds


  • Formed when rocks experience compressive stress and deform plastically, causing bending of rocks. Three types: monoclines, anticlines, and synclines.
• Monocline


  A simple bend in the rock layers where the oldest rocks are at the bottom and the youngest are at the top.
• Anticline


  A fold that arches upward where the oldest rocks are found at the center, and the youngest rocks are covered over them at the top.
• Syncline


  A fold that bends downward, with rocks curved down to a center.
• Faults


  • Rocks under ample stress can crack or fracture, with the fracture called a joint. The footwall is the rock that is placed on top of the fault, while the hanging wall is below the fault.
• Normal faults


  The most common faults at divergent boundaries, where the hanging wall drops down in relation to the footwall.
• Reverse faults


  Most common at convergent boundaries, where the hanging wall moves up.
• Strike-slip faults


  Formed when the walls move sideways, either right-lateral or left-lateral. Most common on transform plate boundaries.