Content

• The earth's tectonic plates are made up f 2 types of crust:

  • Continental (Thick [30-50km], less dense)
  • Oceanic (Thin [5-10km], more dense)
• 3 Types of plate boundaries:

  • Constructive (Mid-Atlantic ridge formed from Eurasian and North American Plate)
  • Destructive (Atacama Trench formed from oceanic Nazca plate subducting under continental South American Plate)
  • Conservative (San Andreas Fault formed from Pacific plate and North American Plate)
• Constructive Plate:

  • 2 Plates moving away from one another
  • Magma rises through to fill the gap and then cools
  • Causes Earthquakes and Volcanoes
  • E.g. Mid-Atlantic Ridge
• Destructive Plate:

  • 2 Plates moving towards each other
  • Denser Oceanic plate will subduct under Continental plate
  • Oceanic plate destroyed, creating gas-rich magma
  • Causes Earthquakes and Volcanoes
  • E.g. Atacama Trench
• Conservative Plate:

  • 2 Plates moving sideways past each other or in the same direction at different speeds
  • Crust isn't created or destroyed
  • Only causes Earthquakes
  • E.g. San Andreas Fault
• If 2 continental plates are moving towards each other, then they will form fold mountains (collision plate boundary), an example of this is the Himalayas Mountain Range.
• Volcanoes only occur at constructive and destructive plate boundaries, whereas earthquakes occur at all plate boundaries.
• At destructive boundaries, volcanoes are formed by:

  • Denser oceanic plate subducting underneath continental plate before then being destroyed and turned into magma.
  • This magma rises through cracks in the crust called vents.
  • The magma then rises to the surface and erupts, forming a volcano
• At constructive boundaries, volcanoes are formed by:

  • Magma rising up through the gap created by the plates moving apart
  • This forms a volcano
• Volcanoes typically are found along plate boundaries, although some volcanoes also form over really hot parts of the mantle, known as hotspots. An example of this is Mauna Kea or Mauna Loa in Hawai'i
• Earthquakes occur at any type of plate boundary due to a build-up of tension.
• Tension builds up in these ways:

  • Constructive: Tension builds along cracks in the plates as they move away from one another
  • Destructive: Tension builds when one plate gets stuck as it moves past the other
  • Conservative: Tension builds up when plates that are grinding past each other get stuck
• The plates will jerk past each other before sending out shock waves once pressure is released, those vibrations are the earthquake.
• The point underground which tension is released is known as the focus, whereas the point on the surface above the focus is called the epicentre.
• Earthquakes are measured using the moment magnitude scale:

  • Measures the amount of energy released by an earthquake
  • It is a logarithmic scale, meaning that a magnitude of 7 is 10x stronger than a magnitude of 6
• Earthquakes mostly originate at plate boundaries, but some can occur in the middle of plates.
• Reasons people live in areas at risk of tectonic hazards:

  • They have always lived there
  • In wealthier countries, protection and planning can minimise risk
  • Confidence in the government to support them if an earthquake occurs
  • Minerals from volcanic ash makes surrounding soil very fertile and mineral-rich
  • Volcanoes can be popular tourist attractions so many people nearby have job opportunities in the tourist industry
• The management strategies used to minimise effects of tectonic hazards:

  • Monitoring
  • Prediction
  • Protection
  • Planning
• Monitoring:

  • Earthquakes - Seismometers monitor earth movements
  • Volcanoes - Scientists can monitor small signs (gas escaping, small earthquakes) to detect a possible eruption
• Prediction:

  • Earthquakes - Scientists can forecast where they may occur from monitoring movement of tectonic plates
  • Volcanoes - Can be predicted if scientists monitor them closely
• Protection:

  • Earthquakes - Reinforced concrete buildings, steel-frame strengthened bridges
  • Volcanoes - Strengthened buildings, trenches and barriers to divert lava
• Planning:

  • Future developments can avoid high-risk areas
  • Emergency services can prepare for any hazards
  • People can be educated so they know what to do if a hazard occurs
  • Governments can plan evacuation routes quickly get people out of an area
  • Emergency supplies can be stockpiled