Geography-Plate tectonics and volcanoes

• Lithosphere


  The Earth's surface, broken up into several large pieces called crustal plates or tectonic plates

  
• Crustal plates


  • Float on the denser semi-molten rock beneath them
  • Move very slowly across the surface of the planet, a few centimetres per year
• Primary crustal plates


  • North American
  • South American
  • African
  • Antarctic
  • Indo-Australian
  • Eurasian
  • Pacific

  
• Smaller crustal plates


  • Nazca
  • Cocos
  • Madagascar
  • Okinawa
• Plate boundary/plate margin


  The area where the edges of two plates meet
• Types of plate boundaries

  • Convergent
  • Divergent
  • Transcurrent
• Convergent boundaries


  • Plates move toward each other
  • Cause earthquakes, folding, and volcanic activity
  • About 3/4 of all earthquakes occur along convergent boundaries
  • Rocks buckle and fold, pushed upward to form mountain ranges
  • Oceanic crust is pushed under continental crust (subduction)

  
• Divergent boundaries


  • Plates move away from each other
  • Magma rises and cools, creating new crust
  • Earthquakes and volcanic activity can occur
• Transcurrent boundaries


  • Plates slide past each other
  • Earthquakes can occur
• Volcanic activity


  The rising of molten material within the lithosphere or onto the Earth's surface

  
• Extrusive volcanic features


  • Formed on the surface

  
• Intrusive volcanic features


  • Formed below the surface

  
• Shield volcanoes


  • Mt. Kilauea in Hawaii
• Composite cones


  • Soufriere Hills volcano in Montserrat

  
• Lava plateau


  Incredibly large amounts of basalt lava that erupt and cover many square miles, forming a wide flat plateau
• Lava plateau


  • The Columbian River Plateau, covering 160,000 square km
• Caldera


  A large volcanic depression at least one kilometer in diameter, formed when a volcano empties most of its underground magma chamber in a massive eruption

  
• Caldera


  • Qualibou caldera in St. Lucia, 3.5 km x 5 km in size
• Volcanic plug


  Formed when molten magma cools and hardens inside the vent of an active volcano
• Sill


  Formed when magma flows horizontally between rock layers, cooling to form a horizontal sheet of solid rock
• Dyke


  A vertical sheet of rock formed when magma moving toward the surface cools and hardens
• Batholith


  A very large feature formed when an underground reservoir of molten rock cools and hardens
• Viscous lava


  Thick, flows slowly, erupts explosively and violently, builds steep-sided cones
• Basic lava


  Flows easily, erupts relatively quietly, produces broad volcanoes with gentle slopes (shield volcanoes)