Seafloor Spreading: Meaning & Process

Right from the beginning, the entire universe is a developmental process, where every moment a new thing is formed and the old one is destroyed. The earth, our planet, is also an element of this universe, and it is undergoing an ongoing developmental process in which new things are formed and old ones are destroyed. One such process is seafloor spreading, under which a new oceanic crust is formed and an older crust is destroyed.

What is the Meaning of Seafloor Spreading?

Proposed by an American geophysicist, Harry H. Hess, in 1960, seafloor spreading is a geological process that can usually be seen at mid-ocean ridges. Under the process, there is a steady development of new oceanic floor (or technically crust), which accordingly keeps pushing the older floor (or crust) away from the ridge because of the volcanic activity (see in the given image).

Historical Background

In an Atlantic sea exploration, with the help of sonar technology, Hess mapped out the ocean floor and traced the mid-oceanic ridge (specifically the mid-Atlantic ridge). Through his detailed study, he found that the temperature near the mid-Atlantic ridge is warmer, and as he goes away from the ridge, the temperature keeps decreasing. He explained that the reason for such high temperatures near the ridge is the constant leakage of magma from the ridge, known as volcanic activity.

Hess discovery further supported the Continental Drift Theory proposed by Alfred Wegener and Alexander du Toit. In 1912, Wegener explained that the continents in motion plowed through the fixed and immovable seafloor. In addition, after a few years, the theories of continental drift and seafloor spreading were merged into a new theory known today as plate tectonics.

Process of Seafloor Spreading

As discussed above, the process of seafloor spreading starts at the mid-oceanic ridge, and such a process begins because of the excessive hot and molten mantle continuously keeps heating the base of the oceanic crust through the convectional current (of heat). Because of unceasing and excessive heating, the crust becomes more plastic, which has a lower density. The convectional current further heats and forces the less dense region upward; as a result of this, this region rises and takes the shape of a broad dome.

As this process continuously keeps happening, which means the region keeps heating and the bulged region further bows upward, and at a point, it fractures, and magma starts coming out, which gradually takes the form of a rift. And, the magma coming out through such a process spreads and cools either side of the rift and eventually forms an oceanic floor (or crust).

Likewise, the younger oceanic crust formed through such a volcanic process causes the spread of the ocean floor. The newly formed crust (or rock) pushes the older crust away from the ridge. The process keeps happening until the newly formed rocks reach a destruction point, i.e., near the oceanic trench, and likewise, the endless process keeps happening. It is estimated that the process of seafloor spreading renews the oceanic floor in every 200 million years, i.e., the period of time for building a mid-oceanic ridge, moving away across the oceanic basin and subducting into a trench.

Evidence of Seafloor Spreading

Following are some of the scientific explanations that structurally explain the process of seafloor spreading −

Presence of Molten Rocks Around the Oceanic Ridge

Hess’ finding of warmer temperature near the mid-Atlantic ridge, has given proof of the presence of molten rocks underneath the ocean. Furthermore, because of the higher temperatures near the ridge, the physical condition and structure of the mid-oceanic ridge are visibly different from the regions located away from the ridge. Hess explained that because of the convection current, magma continuously rises up from the mantle and begins the cycle of formation of oceanic ridges.

Age of Rocks

In seafloor drilling, it is found that the rocks found near the ridge are of younger age, and as they keep going away from the ridge, the age of the rocks keeps increasing. The younger rocks are thinner and their density is lesser and the older rocks are thicker and their density is relatively denser. It means that the magma coming out of the ridge pushes the older rocks away, and as they do, the cool and become denser and thicker

Magnetic Anomalies

The magnetic surveys of the mid-oceanic ridge discovered the symmetrical patterns of magnetic "bands", i.e., the anomalies either side of mid-oceanic rifts. Further, the magnetic anomalies coincide with the episodes of magnetic reversals and explain alternatively positive and negative magnetism. Positive magnetism explains the earth’s magnetic field and explains the higher magnetic measurement at the location, while negative magnetism explains the reversal of the earth’s field, which means lower field strength. Moreover, these alternative normal and reversed magnetic stripes are found across the oceanic bottom. Interestingly, such magnetic anomalies help in calculating the rate of movement of the oceanic floor.

Seismic Studies

The volcanic activity and concentration of earthquakes along the mid-oceanic ridge prove that the oceanic floor is moving away from the mid-oceanic ridge.

Plate Tectonic Theory

Last but not least, the scientific explanation of the movements of the earth’s crust or plates mechanically explains the concept of seafloor spreading.

Conclusion

Moreover, with the help of plate tectonic theory, the recent studies of all the mid-oceanic ridges found in all the oceans revealed the same movements with the same process. It means the process of seafloor spreading is continuously happening under which a new oceanic crust is being formed along the mid-oceanic ridge and an older crust is being destroyed at the other end.

Frequently Asked Questions

1. Who gave sea floor spreading theory?

In 1960, Harry H. Hess first proposed the sea floor spreading theory.

2. What causes seafloor spreading?

The major reason for seafloor spreading is the mantle’s convection currents that keep magma forcing upward and forcing out at divergent plate boundaries and getting settled on both sides of the rift. This process keeps going on, and the magma gradually cools down and takes the form of a new seafloor.

3. Where on earth is the sea floor spreading taking place?

Usually, the sea floor spreading takes place at the mid-ocean ridge. This is the divergent plate boundary region. Two plates get separated and rift forms, and magma comes out, which eventually forms a new crust (sea floor).

4. What would happen if seafloor spreading stopped?

It is nature’s rule that all the time something is created and something is destroyed. So, seafloor spreading is consistently making a new seafloor (crust) at the divergent boundary. On the contrary, the old crust is getting destroyed at the convergent boundary; this is how the earth’s topography is being balanced by nature. However, if sea floor spreading is halted, the entire earth's topography will be deformed.