Seafloor Spreading | 25 Apr 2022

For Prelims: Seafloor Spreading, tectonic plates, Ring of Fire, Pangea

For Mains: Seafloor Spreading concept and associated geographic features

According to a study that analyzed data from the last 19 million years, Seafloor spreading rates have slowed down by roughly 35% globally.

For this study, researchers selected 18 of the world’s largest spreading ridges (mid-ocean ridges).
- A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance.
By studying magnetic records in the rocks on the oceanic crust, they calculated how much oceanic crust had formed over the last 19 million years.
- Basalt rocks on the oceanic crust contain magnetic properties.
- Their magnetism is influenced by the Earth’s magnetic field when the magma reaches the surface and begins cooling to form the crust.
But the records are incomplete because the crusts get destroyed at subduction zones.
- Subduction zone is a point where two tectonic plates collide, causing one of them to sink into the Earth’s mantle beneath the other plate.

The seafloor spreading hypothesis was proposed by the American geophysicist Harry H. Hess in 1960.
Seafloor spreading is the process of magma welling up in the rift as the old crust pulls itself in opposite directions. Cold seawater cools the magma, creating a new crust.
The upward movement and eventual cooling of this magma has created high ridges on the ocean floor over millions of years.
- However, the seafloor is destroyed in subduction zones, where oceanic crust slides under continents and sinks back into the mantle, and is reforged at seafloor spreading ridges.
The East Pacific Rise is a site of major seafloor spreading in the Ring of Fire.
- It is located on the divergent boundary of the Pacific Plate, the Cocos Plate (west of Central America), the Nazca Plate (west of South America), the North-American Plate and the Antarctic Plate.

Growing mountains on the continents might be one of the factors driving the slowdown (as it causes resistance to seafloor spreading).
- About 200 million years ago, when the supercontinent Pangea start breaking, there weren’t any major plate collisions or related mountain chains.
- The continents were fairly flat back then.
Mature Stage of the Supercontinent Breakup: As Pangea progressively broke apart, new ocean basins formed and eventually, the widely fragmented continents started running into each other.
- This happened, for instance, between India and Eurasia, the Arabian Peninsula and Eurasia as well as Africa and Eurasia.
  - This is a natural consequence of a ‘mature’ stage of supercontinent breakup and dispersal.
Changes in mantle convection could also be playing a role as mantle convection transports heat from the earth’s interior to the surface.
- A mantle is a layer inside a planetary body bounded below by a core and above by a crust.
- Mantle convection describes the movement of the mantle as it transfers heat from the white-hot core to the brittle lithosphere.
  - The mantle is heated from below, cooled from above, and its overall temperature decreases over long periods of time.

Seafloor spreading influences sea level and carbon cycle.
- Seal Level:
  - Increasing the rate of seafloor spreading inflates the ridge. Hot, young lithosphere is forming and moving away from the ridge at a faster rate and moving a greater distance from the ridge before it cools and contracts. So sea level rises.
- Carbon Cycle:
  - Faster rates mean more volcanic activity, which injects greenhouse gases into the atmosphere.