Seafloor Spreading Theory

By BYJU'S Exam Prep

Updated on: September 13th, 2023

Sea Floor Spreading Theory is important for the UPSC Prelim and Main Exam. It opened up a whole new paradigm for the study of Geomorphology. After the Second World War, the understanding of ocean floor significantly changed.

Seafloor Spreading Theory

Mapping of the Ocean floor:

Detailed research of the ocean configuration was done using sonic waves, and it contained a sender and a receiver. It revealed that the ocean floor is not just a plain, but it is full of relief. To map the oceanic floor provided a detailed picture of the ocean relief.

As per this detailed mapping, the oceans were found to have 

  • Submerged mountain ranges called Mid-Oceanic Ridges (MOR): This forms a chain of mountain system within the ocean. It is the longest mountain-chain under the oceanic waters.
  • Abyssal Plains: These are plains that are in between mid-oceanic ridges and the continental margins. These are the regions where the continental sediments that move beyond the margins get deposited.
  • Continental Margins: This is the transition between continental shore and deep-sea basins. They include a continental shelf, continental rise, continental slope and deep-oceanic trenches (deepest regions in the ocean).
  • Oceanic Rise (plateau): It connects the continental slope to the deep sea or abyssal plain, which is around 100-1000 Km wide.
  • Small features: Ridges (small hills), Seamounts, Guyots (flat table top mountains), Submarine canyons are part of the continental margin.

 Seafloor Spreading Theory

Fig 1. Ocean floor configuration

Seafloor Spreading Theory

Seafloor Spreading Theory        

Seafloor Spreading Theory 

Fig 2.  Relief features of Ocean floors


  1. Oceans are not featureless plain. It contains mid-oceanic ridges, rise, trenches, abyssal plain, seamount.
  2. Oceanic rocks sample in terms of age were nowhere more than 200 million years old. Continental rocks are way older than oceanic rocks, and some continental rocks formation are as old as 3,200 million years.
  3. Near mid-oceanic ridges, rocks sample were younger, and near the trenches, rocks are the oldest but less than 200 million years.
  4. On the crest of the mid-oceanic ridges, cracks with the continuous active volcanic eruption were found.
  5. The sediments on the oceanic floor are unexpectedly very thin. Sediments were nowhere older than 200 million years as compared to continental sediments.
  6. Age of rocks and types may similar for any two places equidistant from either side of the crest of the mid-oceanic ridge (MOR).

Based on these observations, scholar Harry Hess (1961) prepared a hypothesis called Seafloor spreading theory.

Sea Floor Spreading Theory: 

As per Seafloor Spreading Theory, the mid-oceanic ridge is the region, where at the crest of oceanic ridges through the rupture of the oceanic crust and the crack continuous new lava eruption thrusts into it, consequently pushing the oceanic crust on either side. It leads to the formation of new material on the ridge. Over the period, ridge material eroded (breakdown and carried away) and settles on the ocean floor forming newer ocean floor. The convection below the oceanic crust drives the two parts of the crust fractured along the ridge on the opposite(divergent) as per convection current theory.

This way, the new seafloor is continuously created near the ridges, and older seafloor continuously moves away from the ridge. The most former part of the seafloor goes down in the trench, and hence that’s where we found the oldest seafloor.

The spreading of one ocean does not affect the other like shrinking of other and the younger age of the oceanic crust made Hess think about the consumption of the oceanic crust. Hess further talked about the ocean floor that gets pushed due to volcanic eruptions at the crest, sinks at the oceanic trenches and gets consumed.

This way seafloor spreading explains volcanism or volcanic activity along the ridge, the formation of the ridge, the formation of the seafloor, convection below the oceanic crust, spreading of the seafloor, the trenches and the respective age of the seafloor from the ridge till the trench.

Seafloor Spreading Theory

Fig 3. Seafloor spreading

Limitations of the Theory:

  1. It does not explain the small features of the ocean floors.
  2. It does not talk about the movement of the continents.
  3. It does not speak in terms of lithospheric regions(plates).


It was the first comprehensive theory to talk about movement and formation of sea floors. Simultaneously other scholars such as McKenzie and Parker, Morgan in 1960 developed a more comprehensive understanding of the movement of the different part of the earth crust (both oceanic and continental) and the related formation. It is explained under the theory of Plate Tectonics.

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