Abyssal plain
Also called: Deep sea plain · Topic: Oceans: Hydrological Cycle, Relief of the Ocean Floor, Temperature and Salinity · NCERT: Class 11, Ch 4 "Distribution of Oceans and Continents"; Class 11, Ch 12 "Water (Oceans)"
Meaning
An abyssal plain (also called a deep-sea plain) is a wide, almost flat part of the deep ocean floor. It lies 3,000–6,000 m below the sea surface, between the foot of the continental margin and the mid-oceanic ridges. Over a very long time, fine clay and silt drift down from above and settle on the floor. This sediment buries the uneven rock below, so these plains are the flattest and smoothest areas on Earth. They matter because polymetallic nodules lie on them. These are lumps rich in manganese, nickel, cobalt and copper, and countries now want to mine them.
Example
The Central Indian Ocean Basin, south of the Indian peninsula, has nodule-rich deep-sea plains. In 1987 India became the first "pioneer investor" for these nodules. It now holds an International Seabed Authority contract for about 75,000 sq km of this seabed.
Don't confuse with
- Continental shelf: the shallow, drowned edge of a continent, usually less than 200 m deep. The abyssal plain is the deep ocean floor, far beyond the continent's edge.
- Oceanic trench (deep): a narrow trench with steep sides, 3–5 km deeper than the floor around it. It forms where one plate sinks under another. The abyssal plain is broad and flat.
Related concepts
- Relief of the ocean floor
- Continental margin
- Continental shelf
- Continental slope
- Oceanic trench
- Mariana Trench
- Puerto Rico Trench
- Sunda Trench