An abyssal hill is a small rise on the floor of an abyssal plain, generally no more than a few hundred metres high. Abyssal hills are among the most common landforms on Earth, though too small for most of our map to name.
Key takeaways
- Abyssal hills are generally no more than a few hundred metres tall and a few hundred metres to several kilometres wide.
- They cover more than 30 percent of the ocean floor, so they are among the most common landforms on Earth.
- They are most abundant on the floor of the Pacific Ocean, which has a mean depth of 4,315 m on our map.
- Most are too small to be named, so our map shows them only as fine texture in the shading.
How abyssal hills work
An abyssal hill is a small elevation on the floor of an abyssal plain [1]. Hills sometimes form large regions called abyssal-hill provinces, but they can also occur in small clusters or alone [1].
They are small by the standards of the seabed: generally no more than a few hundred metres high, and from a few hundred metres to several kilometres wide [1]. In the Pacific, studies describe them as typically 50 to 300 m high, 2 to 5 km wide and 10 to 20 km long [1]. They are also very common, covering more than 30 percent of the ocean floor, and they are most abundant in the Pacific [1].
Two ideas for where they come from are tied to the mid-ocean ridges where new seabed forms. Along the flanks of the East Pacific Rise, hills may form as blocks of crust that are raised and lowered by faulting, and then stretched out over time. They may also form where the ridge produced extra magma and so built thicker crust [1].
Either way, hills are the original rough surface of young oceanic crust. On the flat part of an abyssal plain, sediment has buried them completely or nearly so. Where sediment is thin, hills still stand out above the plain [2].
This site draws shaded relief from the grid, so large hill fields show up as a fine, ridged texture. Individual hills are too small to be named, and most of the seabed is mapped at low resolution, so many hills may not appear at all.
An example from our data
The Pacific is the best place to look. The Pacific Ocean is our largest ocean at 139.1 million km², with a median depth of 4,422 m. Much of that is deep plain, and abyssal hills are most abundant there [1].
The East Pacific Rise is a spreading ridge in the east, and the flanks of such ridges are where abyssal hills may form [1]. The Southeast Pacific Basin is one of 110 basins in our list of named features, and the deepest grid cell found near it is 4,918 m.
On the features page you can see that we name 420 seamounts but no individual abyssal hills. Hills are too small and too many to name one by one.
The thing people get wrong
The word "hill" gives the wrong impression of size. Abyssal hills are only a few hundred metres high at most [1], on a floor that is already several kilometres below the surface. They are low swells, not mountains.
They are also confused with seamounts. A seamount is an undersea volcano that stands as its own feature on the seabed, while a hill is a small rise that usually sits in a group on the plain. Both stand above the plain, but they are different in scale, and only seamounts get names on our map.
Frequently asked questions
How big is an abyssal hill?
Generally no more than a few hundred metres high, and from a few hundred metres to several kilometres wide. In the Pacific they are typically 50 to 300 m high.
What is the difference between an abyssal hill and a seamount?
A seamount is a much taller undersea volcano, usually named and mapped on its own. An abyssal hill is a small rise, often one of thousands in a group.
Sources
- Abyssal hill, Wikipedia.
- Abyssal plain, Wikipedia.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against GEBCO_2026 grid).