The hadal zone is the deepest part of the ocean, below about 6,000 m, and is found almost entirely in ocean trenches. It is named after Hades, the Greek god of the underworld.
Key takeaways
- The hadal zone starts at about 6,000 m, though some sources use 6,500 m.
- About 94 percent of it lies in subduction trenches, according to Wikipedia.
- On our map, 5.3% of the Philippine Sea is deeper than 6,000 m, against 1.8% of the Pacific Ocean.
- Its deepest point is 10,927 m, at Challenger Deep.
How the hadal zone works
The hadal zone is the part of the ocean deeper than about 6,000 m. The word was proposed in 1956 by Anton Bruun, from Hades, the Greek god of the underworld [1]. It extends down to roughly 11 km, and some sources set its top at 6,500 m instead of 6,000 m, a compromise that UNESCO adopted [1].
It sits below the abyssal zone and is almost entirely made of trenches. These are long, narrow, V-shaped depressions [1]. About 94 percent of the hadal zone is in trenches formed at subduction zones, where one plate sinks beneath another [1][2]. Trenches cover less than 0.25 percent of the seafloor but make up over 40 percent of the ocean's range of depths [1]. That is why a tiny area gives such an extreme depth.
Most hadal trenches are in the Pacific Ocean [1]. Life there is sparse but real. More than 400 species were known from hadal ecosystems as of 2020, many found nowhere else, and most animals feed on food that drifts down from above. The only primary producers are bacteria that use chemicals such as hydrogen sulfide rather than sunlight [1].
Because the zone is defined by depth, our grid has a direct measure for it: the share of a sea or ocean that is deeper than 6,000 m. Each ocean and sea page on this site gives that share. The map does not draw the zone as a layer. You can see the hadal areas as the darkest, narrowest parts of the depth colours.
An example from our data
The deepest point in the grid is 10,927 m at Challenger Deep, in the Mariana Trench. Other trenches that reach far into the hadal zone include the Tonga Trench, at 10,755 m in its deepest grid cell, and the Philippine Trench, at 10,090 m. Our grid names 39 trenches in all.
The shares show how small the zone is. In the Philippine Sea, 5.3% of the area is deeper than 6,000 m. The Pacific Ocean is 1.8% hadal, the Atlantic Ocean 0.6% and the Indian Ocean 0.5%. The Arctic Ocean has 0%.
On the 6,000 m step of the slider, the page reports 1% sea remaining, which is roughly the trench ground deeper than that. Remember the slider is a bathtub model that lowers the sea everywhere by the same amount.
The thing people get wrong
The hadal zone is not an area of flat, empty ocean. It is a set of separate trenches, each long and narrow, scattered mostly around the edge of the Pacific. A quick look at the world map suggests the deep sea is one big hole. In fact, the hadal zone makes up just a small share of the ocean, and the average depth of the ocean in our grid is only 4,085 m.
Another mix-up is the depth. Published figures for the deepest point differ from ours by tens or hundreds of metres, because our depths come from the grid's deepest cell near a feature, and the real value depends on the survey and the grid resolution.
Frequently asked questions
How deep does the hadal zone start?
At about 6,000 m. Some sources, including UNESCO, use 6,500 m instead.
How much of the ocean is hadal?
A tiny share. On our map the Pacific Ocean has 1.8% deeper than 6,000 m and the Atlantic has 0.6%.
Sources
- Hadal zone, 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).