What are abyssal plains?

Abyssal plains are wide, flat areas of the deep seafloor.

A sea cucumber seen feeding on an abyssal plain. Image courtesy of NOAA Ocean Exploration, 2026 Cook Islands ROV Exploration. Download largest version (jpg, 1 MB).

Abyssal plain is a common term for any part of the seafloor in the ocean’s abyssal zone (3,000 – 6,000 meters deep, or 10,000 to 20,000 feet) other than prominent features like hills, knolls, ridges, or seamounts. These regions are relatively flat, often very expansive, and covered in sediment.

In the past, abyssal plains were commonly viewed as “ocean deserts” of little value to explorers or scientists. As deep-sea exploration technologies have advanced and we’ve learned more about the abyssal ocean, researchers have discovered that abyssal plains are far more interesting than they first seemed. A wide range of animals survive there: some burrowing through the sediment, others swimming or crawling above it. Some regions where sediment builds up slowly feature polymetallic nodules that took millions of years to form. Abyssal plains have also been identified by recent research as one of the deep-sea habitats most in need of further study.

Food for animals can be scarce on abyssal plains. Unlike habitats such as hydrothermal vents, where hot chemicals form the basis of the ecosystem, the food chain on an abyssal plain often depends on nutrients that sink from surface waters above. Some abyssal animals like sea cucumbers eat small organic particles that fall to the seafloor as marine snow. Other animals have powerful senses that help them identify a food source like a sunken whale carcass from kilometers away, even in the darkness of the deep ocean.

Various sources state that abyssal plains cover anywhere from under 30 percent to over 70 percent of the global seafloor. This huge gap exists because definitions of what regions count as abyssal plains can vary. While the term is most often used to describe any relatively flat portion of the deep seafloor, other sources are more specific. Some recent research in marine geology, for example, only categorizes very flat areas that rise or fall less than 300 meters (980 feet) within a defined area as true abyssal plains. As people keep mapping and exploring the seafloor, our understanding of its structures will continue to improve.