Hazardous Earth

• Why do people live in tectonically active locations?

  • Geothermal energy - Iceland
  • Employment - farming
  • Tourism - Iceland
  • Close to family
  • Trekking
  • Fertile soil - rice paddies and coffee plantations
  • No choice due to poverty
• What happens at Transform plate boundries?

  • At some places, some plates just slide past each other in a shearing motion. 
  • There are no volcanoes that are formed at these plate boundaries, but pressure does build up and is released as seismic waves which cause earthquakes.
  • The most famous example of a conservative plate is in California, where the North American and Pacific plates slide past each other along the San Andreas fault system.
• Hanging wall and foot walls

  Fault plane slopes so upperside is hanging wall, and the lowerside is footwall. When fault plane is vertical there is no hanging wall or foot wall.
• Fault planes and fault trace

  Fault planes - Flat surface that may be vertical or sloping.Fault trace - Line it makes on the Earths surface.
• Fault lines


  • Caused by stress on the crust.
  • When these stresses cause parts of the crust to move towards each other, they will create COMPRESSIONAL FAULTING PATTERNS.
  • Where they cause parts of the crust to move apart they cause EXTENTIONAL FAULTING PATTERNS.
• Features and causes of earthquakes

  • At the point when two squares of rock or plates scour against one another, they stick, pushing against one another, yet not moving.
  • Tensions build and when it becomes too much, the rock fractures along cracks and energy is released as seismic waves.
  • Point inside the crust from where the pressure is released is called the focus. The point directly above is the epicentre.
• Ground shaking and ground displacement

  Severity of ground shaking depends on earthquake magnitude, distance from the epicentre, local geology.Buildings can withstand vertical movements better than horizontal ones its the swaying of structures that is so dangerous to their stability. Ground movements that cause dispalcements of rocks along fault lines can rip apart pipelines
• Liquefaction

  When soil is saturated with water, the vibrations of an earthquake can cause it to act like a liquid. This makes the soil weaker and easier to deform, especially when there is heavy weight on the top
• Supervolcanoes

  • Its a volcano erupts more than 1000km cubed of material in a single eruption.
  • Exist as giant calderas, e.g Yellowstone
• Intra-plate eruptions at hot spots 

  Isolated plumes of convecting heat, called mantle plumes, rise towards the surface, generating basaltic volcanoes that tend to erupt continuously.
• Effusive eruptions at divergent plate boundries

  High sillica and gas content (explosive).Forms shield volcanoes and does not produce ash ONLY lava.
• Types of eruptions

  • Icelandic
  • Hawaiian
  • Strombolian
  • Vulcanian
  • Piniean
  • Vesuvian
• Icelandic eruptions


  • Characterised by persistent fissure eruptions
  • Large quantities of basaltic lava build up vast horizontal plains
  • Example: Deccan Plateaux
• Hawaiian eruptions


  • Involve more noticeable activity than Icelandic
  • Runny, basaltic lava travels down the sides of the volcano in lava flows
  • Gases escape easily
  • Occasional pyroclastic activity occurs but less important than lava eruptions
• Strombolian eruptions


  • Frequent gas explosions which blast fragments of runny lava into the air to form cones
  • Explosive eruptions with large quantities of pyroclastic rock thrown out
• Vulcanian eruptions


  • Violent gas explosions that blast out cooled lava
  • Fragments build up into cones of ash and pumice
  • Occur when there's very viscous lava which solidifies rapidly after an explosion
• Piniean eruptions


  • Produce huge plumes of ash and gas that typically take the shape of a huge mushroom cloud
  • Eruptions can last for days and create a sustained and tall eruption plume
  • Drop a huge amount of tephra, fallen volcanic material, on surrounding areas
• Vesuvian eruptions


  • Involve very large blasts of gas that force large ash clouds into the sky
  • More violent than Vulcanian eruptions
  • Ash falls on the surrounding area
  • Lava flows can also happen
• Cinder cone volcanoes


  Airborne pieces of lava, called tephra, are launched out from a solitary vent. The lava cools quickly and falls as cinders that develop around the vent, framing a pit at the summit. Cinder cone volcanoes are genuinely little, for the most part just around 330 feet (99 meters) tall and not rising in excess of 1,210 feet (369 meters). They can develop over brief times of a couple of months or years.
• Composite (stratovolcanoes) volcanoes


  They are worked of layers of substituting lava stream, debris and squares of unmelted stone. Pressure builds up in the magma chamber as gases, under monstrous warmth and weight, are broken down in the fluid stone. At the point when the magma arrives at the conduits, the pressure is discharged and the gases detonate.
• Shield volcanoes


  They have wide bases a few miles in measurement with more extreme center inclines and a summit. Ejections of these volcanoes are not commonly dangerous, however, are progressively similar to fluid flooding around the edges of a holder.
• Hotspot theory

  • There are many areas of instense volcanic activity that are not near any plate margins called hotspots. These are caused by magma plumes.
  • The extra hot magma plume from deep within the Earth rises up through the crust to reach the surface.
  • Magma plume remains stationary over time, but the crust moves above it.
  • Volcanic activity that was above it, decreases as it moves away.
  • New volcanoes form in the crust that is now above the magma plume. As the crust continues to move, a chain of volcanoes form. (Archipelago)
• What happens at Divergent plate boundaries


  1. Plates are moving away from each other

  2. Magma is rising through the asthenosphere and forcing its way to the surface
• Divergent plate boundaries


  Plates are moving away from each other
• Divergent plate boundaries take place most commonly at mid ocean ridges hidden 2.5km below the Ocean's surface
• Mid-Ocean Ridges

  • Consist of very long chains of mountains - sometimes rising 3000m above the seabed - combined length of 60,000km
  • They are not continuous, they are broken up by transform faults
  • Transform faults displace the ridge sideways by tens or in places hundreds of kilometres
  • Volcanic activity is absent along transform faults, but as they slip, energy is released in the form of earthquakes
  • Vary in size depending on the rate of spreading which is determined by the amount of magma and the rate rising to the surface due to convection currents
• Eruption of magma along divergent boundaries

  1. Magma cools rapidly and forms mounds called pillow lavas

  2. As magma rises to the surface, the overlying rocks can be forced up into a dome, putting immense pressure on the lithosphere, therefore it eventually fractures along parallel faults

  3. This produces the underwater rift valleys found along mid-Atlantic ridges

  4. This has been known to create some of the worlds biggest volcanic Islands such as in Iceland
• At these mid ocean ridges, sea water seeps into rifts and is superheated - as it rises to the surface it causes chemical changes in basaltic rocks
• Convergent Plate Boundaries - Oceanic and Oceanic

  • Where two oceanic plates meet, the slightly denser one will subduct under the other, creating a trench.
  • As the descending plate melts, magma rises to the surface and forms chains of volcanic islands (Island Arcs).
  • In the Central Atlantic, the North American plate is subducted beneath the smaller Caribbean plate, forming island arcs such as the Antilles.
• Subduction

  1. Causes a deepening of the ocean at the plate boundary

  2. Forms an ocean trench
• Ocean trenches

  Mark the zone where the oceanic crust descends into the asthenosphere
• Convergence of oceanic and continental plates

  Sediments and rocks crumple, fold and are uplifted along the leading edge of the continental plate
• Oceanic plate subduction

  • Angle between 30° and 70°
  • Comes under intense pressure and friction
• Faulting and fracturing in the Benioff zone


  Releases earthquakes
• Subduction

  1. Causes the oceanic plate to melt

  2. Rises as plutons of magma

  3. Volcano formation
• Plate tectonic theory

  Igneous rocks contain iron particles. As lava erupts, it cools and the magnetic orientation of the iron particles is locked into the rock, depending on the Earths polarity at the time. However, it was discovered that the earths polarity is not constant.Every 400,000-500,000 years, its polarity - palaeomagnetism.Seafloor-spreading is the theory that oceanic crust forms along mountain zones and spreads out laterally away from them. Eventually the sea floor reaches an ocean trench where material is subducted into the asthenosphere and becomes semi-molten.
• What is the continental drift?

  • Wegeners theory is that all continents were joined together as one large mass of land, called Pangaea, and then the land spread apart and drifted into their current positions.
  • Geological evidence for his theory is that some mountain chains and some rock sequences on either side of oceans show great similarity.
  • Biological evidence for his theory is that fossils from rocks younger than the carboniferous period show fewer similarities suggesting that they followed different evolutionary paths.
• What does the upper mantle consist of?

  • Above is a rigid layer sandwiched between the crust and the asthenosphere which is the lithosphere.
  • The layer that extends from 100km to 300km is known as the asthenosphere.
  • Within the asthenosphere, convection currents exist, caused by heat in the mantle.
• What caused the Japan, Tohoku 2011 Earthquake

  • Occured along the Pacific and North American plate boundaries. 
  • Epicentre was 70km offshore of Honshu Island
  • 9.0 Mw
  • The amount of energy released in this single earthquake was 600 million times the energy of the Hiroshima nuclear bomb
  • Undersea mega-thrust earthquake
  • The earthquake triggered a tsunami which reached heights of 40m when it reached the coast.
• Social impacts of Japan, Tohoku 2011 Earthquake

  • 16,000 dead
  • 6000 injured
  • 90% of deaths were due to drowning
  • 100,000 children sepearted from families
  • 2000 children orphaned or lost one of their parents
  • More than 333000 people had to live in temporary accommodation.
  • Destruction of healthcare, schools, homes
  • Disposing of dead bodies proved to be very challenging because of the destruction to crematoriums, morgues and the power infrastructure. As the result of this many bodies were buried in mass graves to reduce the risk of disease spreading