The deepest ocean trench in the world is the Mariana Trench in the western Pacific, whose Challenger Deep reaches about 10,935 metres below sea level. The next deepest are the Tonga Trench (about 10,800 m) and the Philippine Trench (about 10,540 m); all of the top six are in the Pacific, and the deepest point outside it is the Puerto Rico Trench in the Atlantic at about 8,380 m.
The Ten Deepest Trenches, With Caveats on Every Depth
An ocean trench is a long, narrow depression in the seafloor formed where one tectonic plate sinks beneath another in a process called subduction. Depths below 6,000 metres are known as the hadal zone, named after Hades. Trench depths are measured by ship-mounted sonar and occasionally by pressure sensors on landers and submersibles, and published figures for the same point can differ by 50 metres or more. The values below are best current approximations of each trench's deepest known point:
- Mariana Trench (Challenger Deep), western Pacific — about 10,935 m
- Tonga Trench (Horizon Deep), southwest Pacific — about 10,800 m
- Philippine Trench (Emden Deep), western Pacific — about 10,540 m
- Kermadec Trench, southwest Pacific — about 10,000 m
- Izu–Ogasawara Trench, northwest Pacific — about 9,800 m
- Kuril–Kamchatka Trench, northwest Pacific — about 9,600 m (an older Soviet sounding of 10,500 m is now considered unreliable)
- Puerto Rico Trench (Brownson Deep), Atlantic — about 8,380 m
- South Sandwich Trench (Meteor Deep), South Atlantic — about 8,270 m
- Peru–Chile Trench (Richards Deep), eastern Pacific — about 8,060 m
- Japan Trench, northwest Pacific — a little over 8,000 m
Every one of these is deeper than Mount Everest is tall. Everest rises 8,849 metres; set it on the floor of Challenger Deep and its summit would still sit roughly 2 km under water.
Challenger Deep: Why the Deepest Number Keeps Changing
The Mariana Trench curves for about 2,550 km east of the Mariana Islands, southwest of Guam. Its deepest point takes its name from HMS Challenger, the British survey ship whose 1875 soundings first revealed extreme depths here, and from a later Challenger that located the deep itself in 1951.
Its official depth has moved repeatedly. The Soviet research ship Vityaz reported 11,034 m in 1957, a figure still repeated in older books but now rejected. A 2010 multibeam sonar survey by the University of New Hampshire produced 10,994 m, with a margin of error of about 40 m. Then, in 2021, a study combining sonar with pressure readings from repeated submersible dives estimated the deepest point at 10,935 m, plus or minus about 6 m. Most scientists now treat that as the most reliable figure — but the older 10,994 m figure is still widely quoted, so expect to see both.
At the bottom, the water pressure is roughly 1,070 bar, more than 1,000 times the pressure at sea level. Water temperature is only 1 to 4 °C. Since 2009 much of the trench has been protected within the Mariana Trench Marine National Monument, created by the United States. Our Mariana Trench geography guide goes deeper into its setting and exploration.
Old, Heavy Seafloor: Why the Western Pacific Holds the Records
Trench depth is not random. It depends mostly on the age of the plate being subducted. Ocean crust forms hot at mid-ocean ridges and then cools, thickens and becomes denser as it moves away over tens of millions of years. The oldest seafloor in the Pacific, much of it formed during the Jurassic around 150 to 180 million years ago, lies in the western Pacific — and that cold, heavy lithosphere sinks steeply into the mantle, dragging the seafloor down into deep, narrow trenches.
Two more factors help. The western Pacific trenches are far from the mouths of large rivers, so little sediment arrives to fill them in; by contrast, trenches off the Pacific Northwest coast of North America are so buried in sediment that they barely show on the seafloor. And the Mariana system is an ocean–ocean subduction zone, where the Pacific Plate slides under the smaller Philippine Sea Plate, rather than beneath a thick continent.
The same subduction zones make the western Pacific the most violent part of the Pacific Ring of Fire. The Japan Trench was the source of the magnitude 9.0–9.1 Tōhoku earthquake of 11 March 2011, during which the seafloor near the trench shifted by an estimated 50 metres. Across the Pacific, the Peru–Chile Trench — the longest in the world at around 5,900 km — produced the largest earthquake ever recorded, the magnitude 9.5 Valdivia earthquake of 22 May 1960.
Tonga and Kermadec: The Southern Pacific Pair
The Tonga and Kermadec trenches form one continuous subduction system running northward from near New Zealand's North Island toward Samoa. Here the Pacific Plate dives beneath the Australian Plate, and at the northern end of the Tonga Trench GPS stations have measured some of the fastest plate convergence on Earth, around 24 cm per year — several times faster than most plate boundaries.
The Tonga Trench's Horizon Deep, at about 10,800 m, makes it the deepest trench in the Southern Hemisphere. The volcanic arc parallel to the trench is where Hunga Tonga–Hunga Haʻapai erupted on 15 January 2022, sending an atmospheric pressure wave around the planet several times.
The Kermadec Trench to the south is slightly shallower, at about 10,000 m, but has been one of the most studied hadal environments. Baited cameras dropped there have filmed dense swarms of amphipods and the supergiant amphipod Alicella gigantea, which can reach about 34 cm long and has been recorded at depths of more than 6,000 metres.
Beyond the Pacific: Puerto Rico, South Sandwich and Java
Only a handful of trenches exist outside the Pacific, and none reaches 9,000 metres.
- Puerto Rico Trench — about 800 km long, it marks the boundary where the North American Plate moves obliquely past and beneath the Caribbean Plate. Its Brownson Deep, at about 8,380 m, is the deepest point in the Atlantic Ocean. The region's history of large earthquakes, including the 1918 San Fermín earthquake and tsunami off western Puerto Rico, makes it a tsunami concern for the Caribbean.
- South Sandwich Trench — a tight arc about 965 km long east of the South Sandwich Islands, where the South American Plate subducts beneath the small South Sandwich Plate. Its southern end, Factorian Deep, at about 7,430 m, is the deepest point of the Southern Ocean.
- Java (Sunda) Trench — running some 3,000 km along Sumatra and Java, it is the deepest part of the Indian Ocean at about 7,200 m. The Sunda megathrust along this trench produced the magnitude 9.1 earthquake and tsunami of 26 December 2004.
The Arctic Ocean has no subduction trench at all; its deepest point, the Molloy Deep in the Fram Strait west of Svalbard, is about 5,550 m and lies on a spreading boundary.
An Ocean Trench Versus the Grand Canyon
Trenches are sometimes described as "underwater canyons", but the two are made in opposite ways. The Grand Canyon in Arizona is about 1.8 km deep at its deepest and was carved by erosion: the Colorado River cut down through rock layers over roughly the last 5 to 6 million years as the Colorado Plateau rose. Its walls expose nearly two billion years of geological history.
An ocean trench is not carved at all. It is a fold in the Earth's surface, pulled downward where one plate bends and sinks into the mantle. Challenger Deep is about six times deeper than the Grand Canyon, and the Mariana Trench is roughly 2,550 km long compared with the canyon's 446 km. The true underwater equivalents of the Grand Canyon are submarine canyons such as Monterey Canyon off California, which are cut by sediment-laden currents flowing down the continental slope. The full comparison is in is the Grand Canyon deeper than the Mariana Trench?
Who and What Has Reached the Bottom
On 23 January 1960, Jacques Piccard and US Navy Lieutenant Don Walsh reached Challenger Deep in the bathyscaphe Trieste. Nobody returned for 52 years, until film director James Cameron made a solo dive in Deepsea Challenger on 26 March 2012. On 28 April 2019 Victor Vescovo reached it in the submersible Limiting Factor, during a Five Deeps Expedition that visited the deepest points of all five oceans. Because that vehicle could dive repeatedly, around two dozen people had reached Challenger Deep by 2022, among them the former astronaut Kathy Sullivan, who in 2020 became the first woman to do so.
Life was waiting at every depth they reached. The trench floor supports amphipods such as Hirondellea gigas, sea cucumbers and giant single-celled organisms called xenophyophores. Fish have a limit, though: the deepest fish ever filmed is a snailfish recorded at 8,336 m in the Izu–Ogasawara Trench in 2022, and physiologists think fish cannot survive much below about 8,200 to 8,400 m because of how pressure affects their proteins.
Humans have left a mark too. A plastic bag has been documented at around 10,900 m in the Mariana Trench, and studies of amphipods from several hadal trenches have found microplastics and industrial pollutants in their bodies. The hadal zone covers less than 2% of the seafloor but spans nearly half of the ocean's full depth range, and it remains among the least-mapped places on Earth. To test how well you know the oceans these trenches sit in, try the world geography quiz.