What is the Atlantic dorsal?

The Dorsal Atlantic , Mesoatlántica or dorsal Average of the Atlantic is a volcanic mountain range that divides the Atlantic Ocean of North to South.

It has a length of about 15,000 kilometers covering both the North Atlantic, from the north of Iceland and the South Atlantic (at a point south east of South America that is located 7,200 kilometers from that subcontinent). It is part of the Dorsal ocean .

Dorsal ocean

The volcanic mountain range is submerged in the water, so that the dorsal makes the surface of the Atlantic Ocean break in several islands that can be grouped in the middle of the sea.

Of all the islands that are located from North to South, only those of San Pedro and San Pablo have a volcanic origin, unlike Iceland, Ascension, Tristan sa Cunha, Santa Elena and Bouvet, that are not.

Extension of the Atlantic ridge

It should be noted that the extension of the largest part of the Atlantic ridge occupies about 3,000 to 5,000 meters below its surface.

From its seabed there is a long mountain range whose summits, sunk in the water, rise to several meters of height that oscillate between the 1,000 and the 3,000 meters.

On the other hand, the Atlantic dorsal has an extension that can go across, that is to say that it occupies approximately the 1,500 kilometers measured from East to West.

It is well known that the Atlantic ridge has a large cleft, ie a deep valley that runs the length of its ridge. Its estimated width is around 10 kilometers and its walls are authentic walls that reach a height of up to 3 kilometers.

In sum, this valley forms a natural border that at the bottom of the Atlantic Ocean divides the two tectonic plates found on Earth. Its widening occurs constantly, at a rate of 3 centimeters a year.

Due to the high volcanic activity inside, the area where the seabed opens up tends to be nourished by its rapid ascent. That is, the magma, when it rises, then cools, and later becomes a new layer that joins the ocean floor.

The dorsal Atlantic has fracture zones. The best known is the fracture of Romanche, which runs east to west. It also has discontinuities whose length exceeds 100 kilometers in length.

Discovery and research

XIX century

The existence of the Atlantic dorsal was already intuitive in the nineteenth century, but could not be confirmed until the twentieth century. The first clear indication of this was a finding that was categorized as spectacular.

It is stipulated that everything happened about the year 1853 during a work for the installation of a cable through the Atlantic Ocean that extended the international communications. This was inferred three years earlier by the American oceanographer Matthew Fontaine Maury .

As has been said, the transatlantic cable was the starting step for this discovery. In order to make that cable properly installed, it was necessary to measure the depth of the ocean.

For this, exhaustive surveys were necessary. In these, it was noted that there were clear evidence of an underwater plateau beneath the water, in the middle of the Atlantic Ocean. However, this particularity was not given much attention, so it quickly fell into oblivion.

Almost 20 years passed before a British naval expedition, which was led by the corvette HMS Challenger , Gave new light in 1872. The English oceanographic mission checked what had been found in 1853 and found, of course, that the sides of the Atlantic Ocean were deeper than its central zone.

Polls, however, continued throughout the length of the ocean line and this method continued for much longer in what remained of the nineteenth century.

The twentieth century

The nineteenth-century finds, continued by men like the Scottish naturalist Charles Wyville Thomson (1830-1882), were complemented in 1922 by the German naval expedition by the ship Meteor.

On this occasion, the survey of the Atlantic Ocean was much more methodical. It was nothing more to test the ground to install telegraph cables, but made a thorough study of the sea area through ultrasonic instruments.

Afterwards, a team of scientists managed to achieve the goal: a huge mountain range under the sea that crossed the Atlantic Ocean, with a serpentine form.

What was peculiar was that while the lower peaks remained imperceptibly submerged in the water, the highest peaks were in front of their eyes: they were the Atlantic islands, such as Tristan da Cunha, Ascension and the Azores. But that was not even half of what was yet to be discovered.

More profound surveys were carried out in other areas of the Atlantic Ocean in those years. Indeed, it was discovered that the newly found mountain range passed through New Zealand and Africa. This means that the Atlantic dorsal was not content to cross the Atlantic Ocean, but extended far beyond, to the Pacific Ocean.

In addition, scientists realized that the Transoceanic dorsal was what they had mistakenly taken as the dorsal of the Central Atlantic.

In this way, the experts, in addition to making new discoveries, corrected the previous ones. From the 1920s until the late 1940s, scouts scanned the Atlantic using methods that were already used to find German submarines during World War II.

This method was quite familiar to them and allowed them to correctly interpret the results of their investigations, in which they showed unmistakable signs of a novelty.

After that war, oceanographic and geological works resumed their normal activities. By then the scientists knew that there were a number of radical differences between the underwater mountain ranges and those on the continent.

The former were a composition of pressed basalt that covered all its structure from head to toe, very unlike the second, which had in their composition sedimentary rocks.

It was in the 1950s, and more specifically in 1953, that discoveries were made that could be cataloged as revolutionaries.

The team of North American scientists, headed by the geologist Bruce Charles Heezen , Noted that there were more landforms on the bottom of the Atlantic Ocean than had initially been believed. To his surprise, Heezen's group found that in the center of the Atlantic ridge was a very deep ravine.

This finding was key to corroborate what the previous work of Maury, the HMS Challenger and Thomson team in the nineteenth century had detected.

That ravine was the bottom of the ocean, and its sides were but its walls, which supposedly were the slopes of a giant underwater plateau.

Such trait, in fact, extended throughout the Atlantic ridge and not just a portion of it. That is why some scientists christened this area as the Great Crevice of the Globe.

In sum, the Atlantic ridge was found to be longer than they had imagined, for it also passed through the Red Sea, circled the Pacific Ocean coast, and passed through California (particularly in its gulf, The west coast of the United States).

The scientists did not doubt, of course, that the Great Crevasse was about 60,000 kilometers long, but they noticed that it was discontinuous, with sections disconnected by seismic and volcanic action.

By the 1960s there were more expeditions, such as the DSDP Project in 1968 and the Mohole Project that lasted from 1961 to 1966. The latter was discontinued due to economic problems.

In both cases, more than a survey was sought along the dorsal Atlantic (whose length was already well known along with its intense volcanic and seismic activity). Hence a focus was taken on which samples of rocks and sediment were taken.

Importance of these discoveries

Findings around the Atlantic dorsal did not go unnoticed, especially with the evidence revealed during the twentieth century.

In the first place, the relevance of these works is that it could be verified beyond reasonable doubt that the theory of continental drift, postulated by Alfred Wegener , Had absolute validity.

Second, the presence of the Atlantic dorsal gave rise to further support for the idea that the Earth began in the form of a supercontinent called Pangea.

Most important features

Geological characteristics

After studies carried out over more than a century, it has been observed that the Atlantic ridge basically consists of a very deep valley whose shape is sinusoidal.

That is, a long winding line that, as noted above, is interrupted in several of its sections due to the intervention of the volcanoes and the underwater earthquakes so frequent in that part of the Earth. This line leaves a clear separation in the tectonic layers that are located in the continents that it crosses.

It is also worth remembering that the terrain of the Atlantic ridge is formed by the hot magma that tries to climb to the surface, but that is encountered with the oceanic waters.

This causes it to cool down and cause a submerged volcanic eruption to emerge from a hardened lava wall that becomes the new layer of soil on the seabed. Each year new centimeters of geological plates are added whose thickness is constantly increasing.

In addition, the Atlantic ridge is subdivided into two branches; A northern branch, which is the dorsal North Atlantic, and a southern branch, which is the South Atlantic Ridge.

In this last one is located a species of marine trench, or rather a break, a fracture that is known like the one of Romanche and that sinks until the 7,758 meters. It is, therefore, one of the deepest submarine sites in the Atlantic Ocean.

Geographic characteristics

The Atlantic dorsal begins its route in Iceland and ends in the South of the Atlantic Ocean. It connects with the South of Africa by the Cape of Good Hope until passing by the Indian Ocean ridge.

From there it passes to the South of Australia by means of the dorsal of the Pacific Ocean, that is extended by all its southern and eastern zone until arriving at the territory of Mexico, where it touches the western coast of the United States, in California.

There are secondary dorsal to the Atlantic, which in turn can be transverse or parallel. Among them, are the dorsal of Hawaii, the Dorsal Pacific And those of Kerguelen .

Nowadays, the ridges that maintain their tectonic activity occupy surfaces that are directly proportional to the continents with which they limit.

In addition, along the course of the Atlantic ridge are many islands and archipelagos of volcanic origin. In total there are nine islands that are in the middle of the Atlantic ridge. In the North Atlantic ridge are Iceland, San Pedro, Azores and Jan Mayen.

For its part, the South Atlantic Ridge is made up of the islands of Bouvet, Tristan da Cunha, Gough, Santa Elena and Ascension. In the particular case of Iceland, the Atlantic ridge passes right through the middle, so it literally divides it in half.

It is possible to emphasize a particularity of the Atlantic dorsal that serves as proof for continental drift and consequently of plate tectonics.

The fact is simple but transcendental: the fracture of Romanche, mentioned above, draws an imaginary horizontal line through the Equator. But the surprising thing is not that, but the edges of the Gulf of Guinea and the northeastern coast of Brazil fit together and indicate that Africa and America were continents that once were united.

References

  1. Mgar: History, Navigation (No year). Seabed 2; Atlantic Dorsal. Canary Islands, Spain. Retrieved from mgar.net.
  2. Burke, K. (1976). "Development of graben associated with the initial ruptures of the Atlantic Ocean". Tectonophysics, 36 (1-3), pp. 93-112.
  3. Encyclopædia Britannica (2010). Mid-Atlantic Ridge. London, United Kingdom. Retrieved from britannica.com.
  4. Ewing, W.M.; Dorman, H.J. Et al. (1953). "Exploration of the Atlantic Ocean Mid-Ocean Canyon". Bulletin of the Geological Society of America, 64, pp. 865-868.
  5. Geological Society of London (2017). Mid-Atlantic Ridge. London, United Kingdom: GSL. Retrieved from geolsoc.org.uk.
  6. Spencer, Edgar W. (1977). Introduction to the Structure of the Earth, 2nd edition. Tokyo: McGraw-Hill.
  7. UNESCO (2017). The Mid-Atlantic Ridge. Paris, France: UNESCO World Heritage Center. Recovered from whc.unesco.org.
  8. U.S. Geological Survey (2014). Understanding plate motions. Virginia, United States: USGS. Retrieved from pubs.usgs.gov.

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