Oceanography
General introduction
- The Earth’s surface is divided into major two types: oceanic, with a thin dense crust about 10 km thick, and continental, with a thick light crust about 40 km thick which are also known as first-order relief features.
- The ocean and seas cover 70.8% of the surface of the earth, which amounts approximately to 361,254,000 km2.
- The study of the ocean is oceanography which focuses on the study of physical properties and dynamics of the ocean.
- The average depth of oceans is 3800m
- Hypsographic or hypsometric curve is a technique used for measuring the ocean depth as well as elevation of a relief.
Major Ocean relief features

- Continental shelf
- Continental slope
- Continental rise
- Deep sea plains
- Deep ocean Trench
- Continental shelf
- The continental shelf extends seaward from the shore with an average gradient of 1 in 500.
- Average depth of the continental shelf is 200m.
- Average slope of the continental shelf is 1 degree.
- It covers approximately 7.5% total ocean cover.
- Worlds 20% production of crude oil and natural gases are come from continental shelf.
- Continental slope
- Average slope of continental slope is 2 – 5 degree.
- Average depth of the continental slope is 3600 – 4000m.
- It covers approximately 5.5% total ocean cover.
- The percentage of Continental slope in Atlantic Ocean is 12.4%, in Pacific Ocean 7% and in Indian ocean it is 6.5%.
- Continental Rise
- The continental rise is slightly sloping between the continental slope and the deep seabed abyssal plain.
- Average slope is 0.5 – 1 degree.
- Average depth lies in between 2000 – 3000m.
- Deep sea plain
- Average depth of Deep sea plain lies between 3000 – 6000m.
- It covers approximately 75.9% total ocean cover.
- The percentage of deep sea plain in Pacific Ocean is 80.3%, in Indian ocean 80.1% and in Atlantic Ocean it is 54.9%.
- Ocean Trench
- Deepest part of the ocean.
- Generally, trenches are found near to coast line and parallel to the coast.
- World’s deepest trench is mariana trench.
- Normally the ocean trench depth is 5500m.
- Plate tectonic theory is most relevant theory for expanding the origin of ocean trenches.
Trench | Location | Depth |
Mariana Trench | Pacific Ocean | 10,984 m (36,037 ft) |
Tonga Trench | Pacific Ocean | 10,882 m (35,702 ft) |
Philippine Trench | Pacific Ocean | 10,545 m (34,596 ft) |
Kuril–Kamchatka Trench | Pacific Ocean | 10,542 m (34,587 ft) |
Kermadec Trench | Pacific Ocean | 10,047 m (32,963 ft) |
Izu-Bonin Trench (Izu-Ogasawara Trench) | Pacific Ocean | 9,810 m (32,190 ft) |
Japan Trench | Pacific Ocean | 10,375 m (34,039 ft) |
Puerto Rico Trench | Atlantic Ocean | 8,800 m (28,900 ft) |
South Sandwich Trench | Atlantic Ocean | 8,428 m (27,651 ft) |
Peru–Chile Trench or Atacama Trench | Pacific Ocean | 8,065 m (26,460 ft) |


Minor Relief features
- Ridges: Mid-oceanic ridges or submarine stripes are underwater mountain systems formed by plate tectonics activities.

- Seamounts: It is a mountain with pointed tops, rising from the beach that does not reach the surface of the sea.
- Guyots: The flat-topped mountains (seamounts) are known as guyots, eg:- Kuko Guyot (estimated 24,600 km2), Suiko Guyot (estimated 20,220 km2), and the Pallada Guyot (estimated 13,680 km2).
- Coral reefs: Coral reefs are formed by small animal colonies found in seawater that contain certain nutrients (calcium carbonate).