Seafloor Spreading

The concept of seafloor spreading was proposed by Harry Hammond Hess in 1961 (an American geologist). He discovered the mid-Atlantic ridges i.e. mid-ocean ridges. It is a geologic process in which tectonic plates splits apart from each other.

The process of seafloor spreading occurs at mid-oceanic ridges, in which a new oceanic crust is formed through volcanic activities and then gradually moves away from the ridges.

Some Important evidence for seafloor spreading:

  • Along the mid-oceanic ridges, volcanic eruptions are common and they bring huge amounts of lava to the surface in this area.
  • The rocks on either side of the crest of mid-oceanic ridges show similarities in terms of the period of formation, chemical compositions, and magnetic properties.
  • Rocks closer to the mid-oceanic ridges have normal polarity and are the youngest as the age of rocks increases as they move away from the crest.
  • The age of rocks in the oceanic crust is less than 200 million years old. Some of the continental rock formations are as old as 3,200 million years. Thus, ocean crust rocks are much younger than continental crust rocks.
  • The sediments on the ocean floor are very thin. Scientists expected that if the ocean floors were as old as the continent, they would have a complete sequence of sediments for a period of much longer duration. But the sediments column was found nowhere to be older than 200 million years.
  • The deep trenches have deep-seated earthquake occurrence while in the mid-oceanic ridge areas, the quake foci have a shallow depth.
  • According to Hess, constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust, and the new lava wedges into it, pushing the oceanic crust on either side and thus, spreading the ocean floor.
  • The younger age of the oceanic crust and the spreading of one ocean do not cause the shrinking of the other. The ocean floor that gets pushed due to volcanic eruption at the crest, sinks down at the oceanic trenches and gets consumed.
  • In locations where two plates move apart, at mid-ocean ridges, new seafloor is continually formed during seafloor spreading.
  • The newest, Thinnest crust on Earth is located near the center of the mid-ocean ridge. This is the actual site of seafloor spreading.
  • The thickness, density, and age of the oceanic crust increase with distance from the mid-oceanic ridge.
seafloor spreading

Seafloor Spreading events

Significance of Seafloor spreading:

It helps to explain continental drift in the theory of Plate tectonics.  When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere.

The motivating force for seafloor spreading ridges is tectonic plate slab pull at subduction zones, rather than magma pressure, although there is typically significant magma activity at spreading ridges.

  • The spreading rate is the rate at which an ocean basin widens due to seafloor spreading.
  • Spreading rates determine if the ridge is fast, intermediate, or slow.
  • As a general rule, fast ridges have spreading (opening) rates of more than 90 mm/year, the ridges that have a spreading rate of 40–90 mm/year are intermediate, while slow-spreading ridges have a rate less than 40 mm/year.
  • With the help of forces of seafloor spreading and subduction, the shape and diameter of the earth remain constant, as the seafloor creates new crust and subduction destroys old crust. Thus these two forces balance each other.
  • It proves that the ocean itself is the site of tectonic activities.

Triple Junction:

  • Triple Junction is the central point where three cracks split off about 120° angles from each other.
  • Seafloor spreading and the rift valley are common features at “triple junctions.”
Triple junction in Seafloor Spreading

Triple junction in Seafloor Spreading


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Continental Drift Theory - PCSSTUDIES - Geography · November 2, 2021 at 1:46 pm


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