The ocean has great depressions features. The oceans are similar to continents that merge into one another and it is difficult to demarcate them. The oceans are divided by Geographers as Pacific, Atlantic, Indian, Southern Ocean, and the Arctic. These oceans consist of various seas, bays, gulfs, and other inlets.
A major part of the ocean floor is found between 3-6 km below sea level. The land under the ocean is the ocean floor which shows complex and different characteristics similar to those variants on the land. The Bottom relief features of the Ocean Floor consist of rugged mountain chains, ranges, deepest trenches, and large plains.
These relief features are formed similar to continents by tectonic, volcanic, and deposition processes.
Division of Bottom relief features of Ocean
The ocean floor is divided into:
- Continental Shelf
- Continental Slope
- Deep Sea Plain
- Oceanic Deeps
Apart from the above four major divisions, there are also minor divisions such as Ridges, hills, sea, mounts, guyots, trenches, canyons, etc.
It is the extended margin of every continent that is occupied mostly by shallow seas and gulfs. The continental shelf is the shallowest part of the ocean that shows an average gradient of 1° or even less. The continental shelf mostly ends at a very steep slope called the shelf break. The width of the continental slope differs from one ocean to another and its average width is around 80 km.
The continental shelves are mostly absent or very narrow along the coasts of Chile, the west coast of Sumatra, etc. On the other hand, the Siberian shelf in the Arctic Ocean is the largest in the world that stretches about 1500 km in width.
The depth of the continental shelf also differs, it might be as shallow as 30m or as deep as 600m. These shelves are covered with different thicknesses of sediments which are carried down by wind, rivers, glaciers, etc and distributed by waves and currents.
These massive deposits on shelves over a long period of time have become the source of fossil fuels.
It connects the continental shelf and the ocean basins. The continental slope starts where the bottom of the continental shelf sharply drops into a steep slope.
The gradient of the slope region varies between 2-5°. The depth of the continental slope is between 200 to 3000 metre. The boundary of the slope indicates the end of the continents and also Canyons and trenches are found in these regions.
These plains are gently sloping areas of the ocean basins and these are the flattest and smoothest regions of the world. Its depth varies from 3000 to 6000 m. The deep-sea plains are covered with fine-grained sediments such as clay and silt.
Oceanic Deeps or Trenches
Trenches are the deepest parts of the oceans. It is relatively steep-sided and has narrow basins. It is also 3-5 km deeper than the surrounding ocean floor. The trenches are found at the base of continental slopes, near island areas, and related to active volcanoes and earthquakes.
As of now, 57 trenches are founded and out of it 32 are found in the Pacific, 19 found in the Atlantic, and 6 in the Indian ocean.
Minor Bottom relief features of Ocean
Mid Oceanic Ridge
It is two chains of mountains that are separated by a huge depression. These mountain ranges can be as high as 2500 m and some stay at ocean level. Iceland is part of the mid-Atlantic Ridge.
Seamount is a mountain with pointed summits that rises from the seafloor and does not reach the surface of the ocean. These are of volcanic origin, it height are around 300-4500 m.
Example: the Hawaiian Islands in the Pacific Ocean
Submarine Canyons are deep valleys similar Grand Canyon. These are commonly found across the continental slopes and shelves.
Example: Hudson Canyon
Guyots are flat-topped seamounts. This shows pieces of evidence of gradual subsidence through stages to become a flat-topped submerged mountain.
It is estimated that there are 10,000 Guyots in the Pacific ocean.
The atoll is a low island seen in the tropical ocean consisting of coral reefs surrounding a central depression.
These might be part of the sea lagoon or forms enclosing a body of fresh, brackish, or saline water.
This article is written for the topic ‘Ocean bottom relief features’ for Upsc and state service exams. This article includes Continental Shelf, Continental Slope, Deep Sea Plain, Oceanic Deeps, and other minor ocean reliefs.