1. It deals with the nature of the ocean basins of the earth and their topography.
  2. The various seas, bays, gulfs, and other inlets are parts of these four large oceans.
  3. The floors of the oceans are rugged with the world’s largest mountain ranges, deepest trenches, and the largest plains.
  4. The ocean floors can be divided into four major divisions:
    • The Continental Shelf
    • The Continental Slope
    • The Deep-Sea Plain
    • The Oceanic Deeps
divisions of ocean floor

1. Continental Shelf

  1. The continental shelf is the extended margin of each continent occupied by relatively shallow seas and gulfs.
  2. It is the shallowest part of the ocean showing an average gradient of 1° or even less.
  3. The shelf typically ends at a very steep slope, called the shelf break.
  4. The continental shelves are covered with variable thicknesses of sediments brought down by rivers, glaciers, and wind, from the land, and distributed by waves and currents.
  5. It may be as shallow as 30 m in some areas while in some areas it is as deep as 600 m.
  6. Massive sedimentary deposits received over a long time by the continental shelves become the source of fossil fuels.

2. Continental Slope

  1. The continental slope connects the continental shelf and the ocean basins.
  2. It begins where the bottom of the continental shelf sharply drops off into a steep slope.
  3. The gradient of the slope region varies between 2-5°.
  4. The depth of the slope region varies between 200 and 3,000 m.
  5. Canyons and trenches are observed in this region.

3. Deep-Sea Plain

  1. Deep-sea plains are gently sloping areas of the ocean basins.
  2. These are the flattest and smoothest regions of the world.
  3. The depths vary between 3,000 and 6,000m.
  4. These plains are covered with fine-grained sediments like clay and silt.

4. Oceanic Deeps or Trenches

  1. These areas are the deepest parts of the oceans.
  2. The trenches are relatively steep-sided, narrow basins.
  3. They are some 3-5 km deeper than the surrounding ocean floor.
  4. They occur at the bases of continental slopes and along island arcs and are associated with active volcanoes and strong earthquakes.
  5. There are 57 oceanic deeps in the world.
    • Pacific ocean
    • Atlantic ocean
    • Indian ocean.

1. Pacific ocean

  1. There are a total of 32 trenches in this ocean
  2. Mariana or challenger deeps is found in this ocean it is 11033 meters.
  3. Philippines/ Mindanao deep-10498 meters.
  4. The challenger deep is the world’s deepest oceanic deep in the world.
pacific ocean

2. Atlantic ocean

  1. There are a total of 19 trenches in this ocean.
  2. Puerto Rico Trench is the deepest trench at -9382 meters.
trenches in the Atlantic ocean

3. Indian ocean

  1. There are a total of 6 trenches in this ocean.
  2. Most important among them is Java/ sundae trench.
trenches in the Indian ocean