After reading this article you will learn about the meaning of trench.
A long narrow and steep-sided depression on the ocean floor is called a trench. They are deepest parts of the ocean floor and usually 5500 metres deep. The trenches are formed due to tectonic forces—either by down faulting or by done folding.
They generally run parallel to the bordering folded mountains. Trenches are more common in the pacific ocean even though they are found in all the major oceans. The Mariana Trench off the Guam islands is the deepest in the world. It is about 11 km deep.
Canyons are deep valleys with steep slopes found in the continental shelves, slopes and rise. Many canyons have their heads near the mouths of the rivers and extend down the slope to a great depth. Hudson canyon is the best known canyon in the world. The largest canyons occur in the Bering Sea of Alaska.
Banks are formed through the process of erosion. They are more or less flat topped and located in the continental margin. The Dogger Bank in the north sea and the Grand Bank in the north western atlantic ocean are famous examples. The banks are the major fishing grounds of the world.
The reefs are formed by the depositional process of the living or dead coral organisms. They are most common in the Pacific Ocean. The largest reef in the world is found off the north-east coast of Australia.
The study of the reliefs of ocean floor is important mainly for two reasons:
(1) They control the nature, character and the motion of sea water and
(2) Influence the navigation, fishing and other important activities of man.
The bottom reliefs of different oceans are discussed below:
Fig. 5.2: Major submarine relief features.