Earthquakes + Volcanoes

• Where do most earthquakes occur?

  Most occur on plate boundaries
• What percentage of earthquakes occur on the Pacific Ring of Fire?

  90%
• How can earthquakes be caused by plate boundaries?

  By the build-up of pressure and tension
• What happens when the pressure from tectonic plates gives in?

  Huge amounts of energy are released from the focus
• What is the epicenter of an earthquake?

  It is the point on the surface directly above the focus
• What are afterquakes?

  Smaller tremors that occur after the main earthquake
• What scale measures the energy released by an earthquake?

  Moment magnitude scale
• What does the Mercalli scale measure?

  The effects of an earthquake
• What is a deep focus earthquake?

  It has a focus deeper than 70 km below the surface
• Where do deep focus earthquakes occur?

  At destructive plate boundaries
• How do seismic waves from deep focus earthquakes travel?

  They travel vertically and affect a small area
• What characterizes shallow focus earthquakes?

  They have a focus less than 70 km deep
• How do seismic waves from shallow focus earthquakes travel?

  They travel horizontally and affect a wider area
• Where do volcanoes typically form?

  In destructive plate boundaries
• How are volcanoes formed?

  When lava erupts from a vent of magma from the Earth's crust
• What happens to the oceanic plate at destructive plate boundaries?

  It is subducted, destroyed, and melted
• What forms when magma rises through vents and erupts?

  Lava
• What percentage of all volcanoes occur around the Pacific Ocean?

  75%
• What are the two different types of volcanoes?

  Composite and Shield
• How are composite volcanoes formed?

  At destructive plate boundaries with alternating layers of ash and lava
• What type of lava do composite volcanoes produce?

  Thick and viscous lava
• How are shield volcanoes formed?

  On constructive plate boundaries or hot spots
• What type of lava do shield volcanoes produce?

  Thin, runny lava
• What is a hotspot in geology?

  An area far from plate boundaries with intense volcanic activity
• What causes the crust to be hotter than normal in hotspots?

  Magma from the mantle rises and breaks through cracks in the crust
• What are the characteristics of composite volcanoes?

  • Formed at destructive plate boundaries
  • Explosions are more violent
  • Composed of alternating layers of ash and lava
  • Produce thick and viscous lava
• What are the characteristics of shield volcanoes?

  • Formed at constructive plate boundaries or hot spots
  • Less explosive but more frequent eruptions
  • Produce thin, runny lava
  • Have gently sloped sides
• What are the differences between deep focus and shallow focus earthquakes?

  Deep Focus:

  • Focus deeper than 70 km
  • Occur at destructive plate boundaries
  • Seismic waves travel vertically

  
  

  Shallow Focus:

  • Focus less than 70 km deep
  • Weaker and usually not noticeable
  • Seismic waves travel horizontally