An abyssal plain is a flat, underwater plain on the deep ocean floor, usually between the foot of a continental rise and a mid-ocean ridge. It is among the flattest and smoothest places on Earth.
Key takeaways
- Abyssal plains usually lie at about 3,000 to 6,000 m, between the continental rise and a mid-ocean ridge.
- They are flat because fine sediment settles over uneven volcanic rock and fills in the dips.
- Plains cover more than half of the planet's surface according to Wikipedia, which makes them the most common landscape on Earth.
- Our map names 18 abyssal plains, including the Argentine Abyssal Plain.
How an abyssal plain works
An abyssal plain is an underwater plain on the deep ocean floor [1]. It usually lies at around 3,000 to 6,000 m, in the stretch between the foot of a continental rise and a mid-ocean ridge [1].
The seabed under a plain started out far from flat. New oceanic crust forms at the mid-ocean ridges as plates pull apart and magma rises to fill the gap [2]. That young crust is rough, with faults and low volcanic hills. Over millions of years, the crust moves away from the ridge. The whole time a slow rain of fine sediment falls from the water above: mainly clay and silt. Much of it is carried down from the continents by turbidity currents [1]. The sediment settles into the dips and gradually buries the rough rock, leaving a smooth surface.
That is why plains are so flat. Where the sediment is thick enough to cover the hills completely, the surface can be extraordinarily level. Where it is thin, low abyssal hills still poke through.
Plains are not rare. Wikipedia says they cover more than half of the planet's surface [1], which makes them the most widespread landscape on Earth, even though few people will ever see one. They are also among the least explored [1]. Our map draws them as broad areas of even colour. The map does not show sediment thickness or crust type, so its flat colour is only the depth.
An example from our data
Our map names 18 abyssal plains. The Argentine Abyssal Plain in the South Atlantic is at 6,118 m in its deepest grid cell, and 661 km from the nearest land, the Falkland Islands. In the North Atlantic, the Sohm Abyssal Plain is 5,528 m deep and the Madeira Abyssal Plain is 5,403 m.
Their depths are grid values for the deepest cell near each feature, so they can differ from published figures. Each plain sits at its own depth, so there is no single level for them all.
For scale, the Atlantic Ocean has a median depth of 4,242 m, higher than its mean of 3,883 m. That fits an ocean where plains cover large areas. Compare the Pacific Ocean at 4,422 m. You can read more about how our colours handle this on the homepage.
The thing people get wrong
People often assume the deep ocean floor is rugged all the way across. Most of it is the reverse: a vast, nearly level plain. The rugged parts, such as ridges, trenches and seamounts, are the exceptions, and they are narrow compared with the plains.
The other mistake is to think that flat means featureless. Abyssal plains are interrupted by abyssal hills [1] and by volcanic seamounts. A plain is flat compared with the rest of the ocean floor, but it still has relief.
Frequently asked questions
How flat is an abyssal plain?
Among the flattest places on Earth. Fine sediment buries the bumpy volcanic rock beneath, though low abyssal hills still rise through it in places.
How deep is an abyssal plain?
Usually between about 3,000 and 6,000 m. On our map the Argentine Abyssal Plain reaches 6,118 m at its deepest grid cell.
Sources
- Abyssal plain, Wikipedia.
- Understanding plate motions, USGS (This Dynamic Earth).
- Every figure from our own map is worked out from the datasets on the data sources page (checked against GEBCO_2026 grid).