Geography tectonic hazards

  • Created by: T
  • Created on: 27-11-16 15:03




Distribution of Earthquake

Often found in clusters along plate boundaries ( N American and Pacific)  and coast lines ( west coast of N & S America)

·    70% are found in the pacific ring of fire – most powerful ones on convergent and conservative boundaries

·       15% on the Mediterranean belt and 5% in interior plates

·       OFZ – belt of activity through the oceans along mid-ocean ridges, coming ashore in Africa, the red sea and dead sea rift and California

·       CFZ- belt of activity following the mountain ranges from spain, via the alps to the middle east and Himalayas


Distribution of Volcanoes

·       occur at plate boundaries- most along divergent plate margins.

·       These margins includes the mid-Atlantic ridge (between South American plate and African plate and North American plate and Eurasian plate)

·       Many volcanoes have also developed in the region of the Pacific Ocean in a belt aptly called the Pacific Ring of Fire.

·       They do not occur on conservative plate boundaries


Similarities and differences

·       Both occur on plate boundaries

·       Earthquakes found on – convergent, divergent and conservative plate boundaries however Volcanoes now found on conservative

·       Volcanoes found away from plate boundaries – hot spots - Earthquakes found away from boundaries – fault lines


Plate boundaries


Convergent boundary

  • Convection currents cause plates to move together
  • The oceanic crust is denser than continental crust and so when they converge the oceanic plate is subducted in the asthenosphere beneath the continental plate. This melts approximately 100km below the surface.
  • The melted surface (the oceanic crust) is less dense (now) and so it rises through weaknesses in faults and plate boundaries.
  • It may form a Composite volcano- most hazardous and explosive
  • Earthquakes are also common at the Benioff zone where the plates get locked due to the pressure and break away after the release.

·       E.g. the Philippines and Pacific plate tectonic movement in the August 2012 earthquake and September 2013 earthquake.


Divergent boundary  

·       Plates are moving away from each other due to the two convection currents diverging beneath the surface, which leads to magma from the mantle brought up to the surface.

·       There was pressure from the rising magma which led to a doming of the surface and the formation of a ridge. As the plates move apart, cracks and fissures, lines of weakness that allows magma from the mantle to escapes – eg. indian and Eurasian plate

  • Small, frequent and low hazard earthquakes
  • Create rift valley volcanoes – less explosive and effusive – mid Atlantic ridge


Conservative boundary

·       mountains are not made and volcanic eruptions do not happen - crust is not destroyed.

·       2 plates either slide past each other in opposite directions, or 2 plates slide past each other at different speeds.

·       As they move past each other friction




ngl this is only covers 1/3 of the topic