Tectonics

• Where do the majority of tectonic events occur?

  Near edges of tectonic plates (plate boundaries)
• What is the significance of the Pacific ring region in relation to tsunamis?

  Tsunamis with higher wave heights occur near the Pacific ring region
• What causes intra-plate volcanoes?

  Hotspots
• How does a hotspot lead to volcanic activity?

  Magma is hotter than surrounding magma, causing melting of the crust layer
• What are the types of plate boundaries and their characteristics?

  • Convergent (Destructive): Denser plate subducts; forms deep ocean trenches and fold mountains.
  • Divergent: Plates move apart; new crust forms, creating ridges and rift valleys.
  • Conservative: Plates slide past; creates faults with no volcanic activity.
  • **Collision Zone**: Two continental plates collide; can cause
  • shallow focus earthquakes but no volcanic activity, forms fold mountains (Himalayas)
• What is formed when an oceanic plate is subducted beneath a continental plate?

  Deep ocean trenches and fold mountains
• What happens when two oceanic plates converge?

  Deep ocean trenches, underwater volcanoes, and earthquakes occur
• What caused the Indian Ocean tsunami?

  An underwater earthquake between two ocean plates that subducted
• What is the result of friction between continental and oceanic plates?

  Explosive volcanoes and intermediate/deep focus earthquakes
• What occurs at divergent plate boundaries?

  Two plates move apart, leading to new crust formation
• What is an example of a divergent boundary?

  The Mid-Atlantic Ridge
• What type of earthquakes occur at mid-ocean ridges?

  Shallow but minor earthquakes
• What characterizes conservative plate boundaries?

  Two plates slide past each other, creating faults
• What is the San Andreas Fault an example of?

  A transform fault
• What happens when two continental plates collide?

  Neither is subducted, leading to the formation of mountains
• What is the epicenter of an earthquake?

  The point directly above the center of the earthquake on the earth’s surface
• What is the focus of an earthquake?

  The point where pressure is released underground
• Why are shallow focus earthquakes considered more dangerous?

  They are closer to the surface, causing more damage
• What can increase the danger of an earthquake?

  A high population near the epicenter
• What type of waves create the most damage during an earthquake?

  L waves
• How is a tsunami generated?

  Seismic activity causes the ocean floor to be lifted, displacing water
• What happens to tsunami waves as they approach the shore?

  They slow down but increase in height
• What factors influence the nature of a tsunami wave?

  Cause of the wave, distance traveled, water depth, and offshore topography
• What are the hazards associated with volcanoes?

  • **Pyroclastic flows**: Fast-moving flow of ash and gases (e.g., Mount St Helens 1980)
  • **Lahars**: Fast-moving mud flows (secondary impact)
  • **Poisonous gases**: Carbon monoxide, requires detection alarms (e.g., Iceland 2010)
  • Jokulhlaups: Floods from glacial melt (secondary impact, e.g., Iceland 2010)
  • **Ash fall**:Solid material released from volcano- Destroys buildings(Pompeii), Causes respiratory problems, necessitates evacuation (e.g., Iceland 2010)
• What is the Benioff zone?

  A convergent plate boundary where a slab is pulled down into a subduction zone
• What happens in the Benioff zone over time?


  Stress builds up for hundreds of years until released as seismic waves
• When was the theory of Pangaea proposed?

  1912
• Why was the theory of Pangaea not taken seriously initially?

  Due to lack of evidence
• What discovery in the 1950s contributed to the theory of plate tectonics?

  Mapping of the ocean floor led to the discovery of mid-ocean ridges
• What is sea floor spreading?

  Oceanic crust forms along mid-ocean ridges and spreads out laterally
• What was discovered in 1963 regarding new crust?

  New crust has magnetization aligned with Earth's magnetic field
• What did the discovery of alternating patterns of magnetic polarity indicate?

  It showed the history of sea floor spreading over time
• When was the theory of plate tectonics proposed?


  1968
• What type of evidence was used to support the theory of plate tectonics?

  Mathematical evidence
• What is a multiple hazard zone?

  A country that is vulnerable to multiple natural hazards
• Which country is an example of a multiple hazard zone?

  Philippines
• What type of boundary is Mount Pinatubo associated with?


  A destructive plate boundary
• Which indigenous tribe lived on the slopes of Mount Pinatubo during its eruption in 1991?

  Aeta tribe
• Why was the danger of Mount Pinatubo underestimated before its eruption?

  There had been no eruption since 1380
• What was a consequence of growing settlements near Mount Pinatubo?

  Increased risk to the population from volcanic eruptions