The major seafloor features of the ocean are illustrated in this cross section.
The deep-ocean basins represent the areas of the ocean beyond the continental margins. The deep-ocean basins are all made of oceanic crust and have three major seafloor features: oceanic ridges, ocean trenches, and abyssal plains.
- Oceanic Ridges: Similar to mountains on continents, the most dominant feature of the oceans is a long, elevated ridge called the mid-ocean ridge. This 70,000 kilometer (approximately 43,000 mile) long ridge follows a fairly continuous line through all the oceans of the world.
- Ocean Trenches: An ocean trench is a long, relatively narrow, steep-sided depression in the ocean. Ocean trenches are the deepest areas of the ocean. Ocean trenches represent a small part of the ocean floor, but their existence is crucial to understanding the formation of volcanoes (see Unit F – Volcanoes for further details).
- Abyssal Plains: Abyssal plains are large, flat areas in the ocean basins. The Canary Abyssal Plain, for example, west of the Canary Islands in the North Atlantic, has an area of approximately 900,000 km2 (approximately 350,000 square miles). These extensive plains are made of sediment layers that are hundreds of meters thick and that have been deposited on the ocean floor over thousands and thousands of years. Abyssal plains are typically found at depths of 4–6 kilometers (2–4 miles).
Did You Know?
That Is Really, Really, Really Flat!
The abyssal plains are the flattest places on the Earth. The Argentine Abyssal Plain, for example, rises less than 3 meters (10 feet) over a distance of 1,300 kilometers (approximately 800 miles)!
Word Link
Abyssal: The word abyssal originated in the 1690s as a term to describe a zone of water that had a depth greater than 300 fathoms (1 fathom = 1.83 meters = 6 feet). Abyssal was originally based on the 14th century word abyss which was itself derived from the Latin word abyssus meaning bottomless.
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The Deepest Oceanic Trenches
The deepest oceanic trenches in the world are all located in the Pacific Ocean. Below is a list of the world’s five deepest oceanic trenches along with their maximum depths as measured from sea level. Click on each trench name in order to visit it.
- Mariana Trench (11,033 m / 36,197 ft)
- Tonga Trench (10,882 m / 35,702 ft)
- Philippine Trench (10,540 m / 34,580 ft)
- Kuril-Kamchatka Trench (10,500 m / 34,449 ft)
- Kermadec Trench (10,047 m / 32,963 ft)
Click here to see a flat map projection of all five of the world’s deepest oceanic trenches. You can scroll and zoom in on the flat map.