Seafloor spreading is a geological process which involves the splitting of tectonic plates and their movement away from each other. Like all geological processes which involves tectonic activity, seafloor spreading is caused by mantle convection. Mantle convection is the slow churning of the earth’s mantle which takes places beneath the earth's surface. Convection currents transfer heat from the core and mantle of the earth up to the lithosphere, and also carry rocks from the lithosphere deep to the mantle. Seafloor spreading takes place at the boundaries of divergent plates whereby, as the divergent tectonic plates move away from each other, hot convectional currents from the mantle cause the lithosphere (the ocean crust) to become less-dense, ductile, and brittle, and therefore rise above the surrounding crust to form a submarine mountain. In most cases, the brittle lithosphere cracks, allowing hot magma pushed by the convectional currents to spill onto the ocean crust forming a new layer of the ocean crust made up of igneous rock.
History
Scientists originally believed that drifting was an occurrence exclusive to continents through continental drifts. However, technological innovations of the 20th century in the form of precise depth recorders and seismic recorders allowed scientists to discover an immense submarine mountain range which runs under the Atlantic Ocean. The underwater mountain chain would later be named as the “Mid-Atlantic Ridge” and was established to run for many miles on the ocean floor. Scientists would later establish that the Mid-Atlantic Ridge was part of an extensive submarine mountain chain which ran around the world and spanned more than 40,000 miles in length. In some sections, the immense mountain chain had deep rifts which ranged between 20 and 30 miles in width and with an average depth of about 1 mile.
In light of the discovery, Princeton University’s Harry Hess in the 1960s first proposed the notion that the ocean floor did, in fact, move while expanding from a central axis in a process he termed as seafloor spreading. Hess argued that the seafloor was formed as a result of the expansion of mid-ocean ridges as they move in opposite directions from the ridge center.
Research looking into the earth’s magnetic field conducted in the 1960s supported Hess’s theory as the study showed that the ocean floor had elongated patterns of reversed polarity as well as normal polarity in regions parallel to a mid-ocean ridge, only possible if the ocean floor was indeed in motion. Another study which supports Hess’s theory of seafloor spreading is one who analyzed the age of ocean crust rocks and compared them with rocks which make up the continental crust. The study established that rocks making up the ocean crust were not more than 200 million years in age, making them younger compared to continental crust rocks which have a maximum age of 3 billion years. Additionally, the researchers established that the sediment cover gradually thinned near a mid-ocean ridge.
Geographic Features
The process of seafloor spreading leads to the formation of numerous geographical features which can be terrestrial, sub-terrestrial, or marine features. Seafloor spreading is credited for the formation of the Red Sea as a result of the movement of the Arabian and African tectonic plates away from each other. The movement of these two tectonic plates is still ongoing, albeit at a slow pace, and geologists believe that after millions of years, Africa and Asia will completely be separated at the Suez Peninsula, causing the Red Sea and the Mediterranean Sea to merge. The Niger Delta is believed to have been formed through seafloor spreading, as South America, which was originally merged with Africa at Africa’s western coastline, broke off and moved westwards to its current position. As the ocean crust moves against the continental crust, the boundary between the two forms an active plate margin which is highly unstable, and the instability causes the active plate margin as the center of earthquakes and volcanic activity. An example of this geographical feature is the Pacific “Ring of Fire” which has numerous active volcanoes and the epicenter of seismic activity.
Mid-Ocean Ridges
The main geographical feature formed by the process of seafloor spreading are mid-ocean ridges. Usually, these submarine mountain ranges have a valley running on their spine which is known as a rift and is about a mile in depth. While mid-ocean ridges are a submarine features, in some places, the Mid-ocean ridges in the world are all connected and make the Ocean Ridge, which with a total length of 40,400 miles is the longest mountain range in the world. Mid-ocean ridges have ongoing geological activity, with scientists believing that they move several inches each year. Mid-Atlantic Ridge is an example of a mid-ocean ridge, which runs beneath the Atlantic Ocean. The Mid-Atlantic Ridge was discovered in 1872 by scientists on the expedition of HMS Challenger. The Mid-Atlantic Ridge is made up of two parts which are divided by the Romanche Trench near the Equator.
The East Pacific Rise is another mid-ocean ridge is which runs on the ocean floor of the Pacific Ocean. The East Pacific Rise emanates from the Gulf of California and runs southwestwards to New Zealand, and separates the Antarctic Plate from the Nazca Plate, the Cocos Place, the North American Plate and the Rivera Plate. The East Pacific Rise has unique submarine volcanic features known as hydrothermal vents which are home to animal species found nowhere else on earth. The Pacific-Antarctic Ridge is another mid-ocean ridge, which is situated in the South Pacific Ocean and separates the Antarctic Plate from the Pacific Plate. Another mid-ocean ridge is the Southeast Indian Ridge which runs in the southern Indian Ocean. The Southeast Indian Ridge runs a total length of about 3,700 miles between the Macquarie Triple Junction and the Rodrigues Triple Junction, and rises about 500 meters above the Indian Ocean floor along its entire length. The mid-ocean ridge separates the Antarctic Plate from the Australian Plate. Other mid-ocean ridges in the world include The Louisville Ridge, The Chile Rise, the East Scotia Rise, the Central Indian Ridge, the Southwest Indian Ridge, and the Gakkel Ridge, among others.
