Earth's Processes

• Earthquakes


  Occur because of the force i.e. stress happening in rocks
• Diastrophism


  Dynamic internal forces that tend to cause the earth's surface to undergo deformation
• Tectonic movement


  Creates tremendous stress near plate boundaries, which deforms rocks
• Factors that control how a rock responds to stress

  • Nature of the rock
  • Temperature
  • Pressure
  • Time
• Brittle fracture


  Rock fails by shattering when struck, e.g. quartz crystal
• Plastic deformation


  Rock deforms and stays deformed when struck, e.g. gold nugget
• Elastic deformation

  Rock deforms and immediately rebounds when struck, e.g. rubber ball
• Higher temperature

  Greater tendency for rock to deform in a plastic manner
• Higher pressure


  Favours plastic behaviour in rocks
• Slow stress application


  Favours plastic deformation
• Rapid stress application


  Causes brittle fracture
• Geologic structure


  Any feature produced by rock deformation, including translation, orientation change, and shape change
• Types of geologic structures

  • Folds
  • Faults
  • Joints
• Fold


  A bend in rock, formed by ductile deformation
• Characteristics of folds


  • Result from compression
  • Shorten horizontal distances
  • Occur in groups
• Anticline


  A fold arching upward
• Syncline


  A fold arching downward
• Dome


  A circular or elliptical anticlinal structure
• Basin


  A similarly shaped syncline
• Monocline


  An open, step-like structure with layers inclined in the same direction
• Fault


  A fracture along which rock on one side moved relative to rock on the other side
• Why rocks move repeatedly along faults

  • Tectonic forces persist in the same place
  • Easier to move along existing fracture than create new one
• Normal fault


  Forms where tectonic movement stretches and pulls apart Earth's crust
• Reverse fault


  Forms where compressive forces squeeze and fracture the rock
• Thrust fault


  A low-angle (< 30 degrees) reverse fault
• Strike-slip fault


  Vertical or near-vertical fracture where rocks move horizontally past each other
• Footwall


  The side of a fault that is walked on
• Hanging wall


  The side of a fault that hangs over the head
• Joint


  A fracture in rock where there has been no movement on either side
• Joints and faults are important in engineering, mining, and quarrying because they are planes of weakness in otherwise strong rock
• Right-lateral strike-slip fault


  When the side across the fault moves to the right
• Left-lateral strike-slip fault


  When the side across the fault moves to the left
• San Andreas Fault


  A zone of strike-slip faults that form the boundary between the Pacific plate and the North American plate
• Joint


  A fracture in which rocks on either side of the fracture have not moved
• Joints


  • Tectonic forces create them
  • Most rocks near Earth's surface are jointed
  • Become less abundant with depth because rocks become more plastic and less prone to fracturing
• Faults and joints


  Important in engineering, mining, and quarrying because they are planes of weakness in otherwise strong rock
• Dams in jointed rock

  Often leak because water seeps into the joints and flows around the dam through the fractures
• Plate boundaries


  • Divergent - stretching adjacent rock and producing normal faults and grabens but little folding
  • Transform - friction often holds rock together as the plates gradually slip past each other, resulting in folding, faulting, and uplift
  • Convergent - compression commonly produces large regions of folds, reverse faults, and thrust faults, but can also produce crustal extension and normal faulting
• Shortly after World War II, scientists began to explore the floors of Earth's oceans
• Defense strategies wanted a detailed knowledge of sea floor topography for submarine warfare, and the same information was needed to lay undersea telephone cables