Theories on the Origin of Submarine Canyons

The submarine canyons are one of the prominent erosional features along the continental margins and also in the deep-sea environment. Such canyons are found everywhere and across all the oceans.

Historical Background

Initially, canyons were discovered on the Georges Bank based on their exact positions and surroundings, which resulted in the emergence of explanations for various theories. On investigating the Atlantic coast of the United States, the scientist named Francis Sheppard advocated the earliest theory in this regard.

To explain the origin of submarine canyons, the following major theories were put forward.

Diastrophic Theory

According to a few exponents (Andrew, Lawson, De la Roche Ponie, and others), the variations in earth movements and their tectonic consequences (like folding, faulting, warping, etc.) may determine the formation of submarine canyons. Some have observed that the endogenetic forces exerted by the earth cause the effect of tensional forces to give rise to the formation of faults and graben on the continental shelves and slopes. Eventually, these fault-troughs and grabens turn into submarine canyons. On similar lines, synclinal basins and troughs were formed out of the process of warping and steep folding, that later became submarine canyons too.

Some other scientists, like De Andrade, believe that a series of graben-like river valleys are created due to the coastal displacements at the local level, which results in the origin of submarine canyons.

Jensen and Bourcart opined that the submarine canyons along the continental margin are the result of subsidence and drowning of river valleys, and they were formed during the Quaternary period.

Some major examples of the origin of submarine canyons cited based on this theory are canyons found along the coasts of the Pacific Ocean and the Mediterranean Sea.

Criticism

• Faults are generally located parallel to the coasts; rather, submarine canyons are situated transverse to the coast.

• Faulting cannot explain the reason behind the dendritic pattern of the tributaries of submarine canyons.

• Faults are not evidently and necessarily found on all continental shelves and slopes.

Subaerial Erosion Theory

Submarine canyons resemble continental canyons in terms of shape and deposition, and thus few proponents (J.D. Dana, F.P. Sheppard, Hull) believe that submarine canyons form as a result of subsequent drowning of river valleys and submergence of continental margins. Running water in the river, they claim, massively eroded their valleys, resulting in deep gorges, and the channel gradient becomes steeper with each successive rise of land alongside the river valley. Over due course of time, when tectonic movements subside the continental margin or when sea level tend to rise due to the phase of glaciation, long and deep valleys get drowned and form the submarine canyons.

Some typical examples of submarine canyons formed through subaerial erosion are the drowned valleys of the Java Sea, Monterey Canyon, and Philippine Canyon, among others.

Criticism

• This theory has failed to explain the origin of submarine canyons beyond a depth of 2,000 meters.

• W.M. Davis opined that it would require a long geological period for the origin of submarine canyons as cited in this theory.

• The location of submarine canyons farther away from the river mouths questions the application of the theory to some parts of the world.

Submarine Density Current Theory

As shown by the observations made by Holimann and Adolf Von Salis, the origin of submarine canyons and the submarine density currents are related in reasonable ways. The variations in temperature and salinity between the rivers and sea water, cause the density difference that results in the formation of the density currents in front of the river mouths. While the trenches experience sedimentation and the formation of levees due to the presence of stagnant water on either side, the density currents erode the continental shelves and slopes, forming trenches.

Criticism

• The density currents cannot act as a causative factor in the formation of submarine canyons since they are confined to enclosed seas, lakes, and, reservoirs and very rarely occur over shallow continental shelves.

Turbidity current theory

Several exponents (W.M. Davis, W.E. Rither, Tangier Smith, Daly, etc.) argued that the turbidity current is responsible for the formation of the submarine canyons. It is generally observed that strong onshore winds tend to pile up water near the coastline, and as a result, an undercurrent flows towards the sea. The fine materials tend to suspend due to the effect of these undercurrents and known as the turbidity currents. The suspended sediments increase the density of these currents, forcing them to move seaward. The continental shelves get eroded, and submarine canyons are formed as a result.

Criticism

• Many critics question the efficiency and possibility of turbidity currents forming submarine canyons.

Conclusion

Submarine canyons play an important role in reducing continental organic carbon by transporting it to the deep ocean via ocean basin deposits.

Frequently Asked Questions

What are submarine canyons?

Submarine canyons are long, narrow, very deep, and steep-sided valleys or trenches situated on the seabed of the continental slopes and shelves, which have vertical walls that bear a resemblance to continental canyons.

What are the examples of submarine canyons based on the Subaerial Erosion Theory?

Some typical examples of submarine canyons formed through subaerial erosion are the drowned valleys of the Java Sea, Monterey Canyon, and Philippine Canyon.

What is the main criticism observed in the Submarine Density Current Theory?

The major criticism put forward on the submarine density current theory is −

The density currents cannot act as a causative factor in the formation of submarine canyons since they are confined to enclosed seas, lakes, and, reservoirs and very rarely occur over shallow continental shelves.