Abyssal Plain: Definition & Facts

Instructor: Terry Dunn

Terry has a master's degree in environmental communications and has taught in a variety of settings.

If you have no idea what an abyssal plain is, your imagination is likely to come up with some depressing images ('abyssal' sounds pretty close to 'abysmal,' after all). Here you will learn what an abyssal plain actually is, what it looks like and what lives there.

What is an Abyssal Plain?

Abyssal plain? It sounds like a combination of the words 'abyss' and 'dismal.' And those two words might not be that far off when describing an abyssal plain. If you've ever thought the word 'abyss' reminded you of the depths of the ocean, you're on the right track. And the word 'plain' usually means a flat, wide area. Put those two things together and you have an abyssal plain, which refers to the huge, flat areas on the ocean floor.

Flat is almost an understatement. The abyssal plains are some of the flattest features on the planet. Some drop in elevation less than a foot for every 1,000 feet in distance. Sometimes there are small hills called abyssal hills, but generally abyssal plains are as flat as a tabletop. 

Abyssal plains are 2,200 to 5,500 feet below ocean surface and are between the continental rise (the part of the underwater continental margin farthest from the shore) and the mid-ocean ridge (where under-ocean tectonic plates move away from each other, forming volcanoes that turn into underwater mountain ranges) or ocean trenches (where one tectonic plate slides beneath another, in a process called subduction).

Diagram showing the abyssal plain and other ocean features
Ocean floor diagram

What do Abyssal Plains Look Like?

There's more to abyssal plains than just being flat. They are covered in sediment, which is part of the reason they are so featureless. The sediments are brought by ocean currents and by an assortment of debris that rains from above. The sediment includes everything from volcanic ash, dust, organic matter from ocean creatures, nodules made from a mixture of maganese and other minerals, and even bits of meteorites. The rate that sediments accumulate on the abyssal plains make 'glacial speeds' look fast. The sediments stack up only one inch every thousand years. 

Abyssal plains cover more area in the Atlantic and Indian Oceans and less of the Pacific Ocean. Worldwide though, abyssal plains account for 40% of the world's ocean floors.

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