Explain the mechanism of sea-floor spreading and briefly mention the characteristic features of the Mid-Atlantic Ridge. (15 Marks)

Mentors Comments:

  • The question is from the static portions and probes upon the phenomena of SFS and the features of Mid-Atlantic ridge.
  • In the introduction, explain the concept of seafloor spreading.
  • In the main body, discuss:
  • Seafloor spreading is an endo-genetic process occurring at divergent plate boundaries. 
  • Mention details of the characteristic features of Mid-Atlantic Ridges.
  • Use suitable diagrams to ensure the content is holistically conveyed.
  • Conclude with the significance of the phenomena in the formation of geographical features.

Answer:

Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. The idea that the seafloor itself moves (and carries the continents with it) as it expands from a central axis was proposed by Harry Hess.

Image result for seafloor spreading upsc

Mechanism:

  • According to this theory, the intense heat generated by radioactive substances in the mantle (100-2900 km below the earth surface) seeks a path to escape and gives rise to the formation of convection currents in the mantle.
  • Wherever rising limbs of these currents meet, oceanic ridges are formed on the seafloor and wherever the failing limbs meet, trenches are formed.
  • Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
  • Seafloor spreading helps explain continental drift in the theory of plate tectonics. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere.
  • Basaltic magma rises up the fractures and cools on the ocean floor to form new seafloor.
  • Older rocks will be found farther away from the spreading zone while younger rocks will be found nearer to the spreading zone.

Characteristics of Mid-Atlantic Ridge:

  • The continents bordering the Atlantic Ocean, for example, are believed to be moving away from the Mid-Atlantic Ridge at a rate of 1–2 cm (0.4–0.8 inch) per year, thus increasing the breadth of the ocean basin by twice that amount.
  • Volcanic eruptions are common all along the mid-oceanic ridges and they bring huge amounts of lava to the surface in this area.
  • The rocks equidistant on either side of the crest of mid-oceanic ridges show remarkable similarities
  • Rocks closer to the mid-oceanic ridges are normal polarity and are the youngest.
  • The age of the rocks increases as one moves away from the crest.
  • The deep trenches have deep-seated earthquake occurrences while in the mid-oceanic ridge areas, the quake foci have shallow depths.

Seafloor spreading helps explain continental drift in the theory of plate tectonics. Seafloor spreading proposed the magma as the cause of new crust and subduction of crust at the ocean-continent boundaries. This was further expanded by scholars to propose plates and their movement due to this magma. It is these tectonic plates and not the continents that have been moving since the inception of earth.

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