A Brief Note on Submarine Relief

The relief features of ocean floors are much more varied than the relief features on the continents. The submarine relief features are:

(a) Continental Shelf

(i) It is the submerged part of the land adjoining the coast. It is shallow,

(ii) It is broad where the mountains are away from the coast, for example, eastern North America,

(iii) It is narrow where the mountains are nearer to the coast, for example, Western North America and South America,

(iv) The average width of the continental shelf is 70 km.

(v) Continental shelves provide rich fishing grounds, e.g., Grand Bank, off New Found land in North America and Dogger Bank in the North sea. One fourth of the world’s petroleum is produced from oil wells in the continental shelves, e.g., Bombay High.

(b) Continental Slope

(i) It is the edge of the continental block,

(ii) It is a link between the continental shelf and the deep sea floor,

(iii) It is narrower than the continental shelf,

(iv) It has a steep slope.

(c) Abyssal Plain

(i) About 40% of the ocean floor is a relatively flat basin formed by the accumulation of sediments on the sea floor; (ii) Its depth varies from 3000 to 5000 m.

(d) Submarine Ridges

(i) Narrow elongated ridges rise steeply from the abys­sal plain,

(ii) They resemble the ridges on the land, e.g., the Atlantic Ridge is about 16,000 km long. It is the longest ridge in the world,

(iii) the peaks of some of the ridges may rise above sea level to form islands, e.g., the Philippine islands.

(e) Trenches or Deeps

(i) Deep, narrow and steep sided depressions are found in the abyssal plain,

(ii) The trenches are the result of the tectonic forces and their depth may vary from 6000 to 11000 m, e.g., the Mariana trench (11200 m) and Nares deep (8500 m).