Challenger Deep

Challenger Deep is the deepest part of the Mariana Trench, at its southern end in the western Pacific. The trench is a long, crescent-shaped depression east of the Philippines. At depths of nearly 11 kilometres, the water column above the seafloor exerts extreme pressure.

The depth commonly given for Challenger Deep is approximately 10,935 metres (35,876 feet). A 2021 study based on submersible transects reported a deepest observed depth of 10,935 metres, with an uncertainty of ±6 metres at 95% confidence. Its estimate used pressure readings from a submersible, corrected for factors including water-column properties, atmospheric pressure, gravity and water level. Because the bottom is surveyed with instruments rather than a ruler, depth values are measurements with defined methods and uncertainty, not absolute values known without error.

The Mariana Trench formed through subduction: an oceanic tectonic plate moves down into the mantle beneath another plate, bending the seafloor into a deep depression. The region belongs to an active convergent plate boundary. Subduction zones are associated with earthquakes and can generate tsunamis, though the trench's immense depth is a geological feature, not itself evidence that an earthquake or tsunami is occurring.

The British Royal Navy's HMS Challenger expedition made an early sounding of the trench in 1875, using a weighted line and recording 4,475 fathoms. Later surveys used echo sounders, which send sound pulses toward the seabed and infer depth from their return, allowing broad areas to be mapped without sending a person down. Crewed and remotely operated submersibles have also visited the deep basin, where high pressure makes vehicles, instruments and communications especially demanding. New sonar and pressure measurements continue to improve maps and refine estimates of the deepest seafloor.

The trench is a natural setting for studying deep-ocean geology, hadal environments and the limits of life under high pressure, darkness and cold. Its remoteness and the difficulty of reaching the seafloor mean that observations come from a limited number of expeditions and instruments. Mapping the region also helps scientists distinguish the shape of the trench and its basins from the changing precision of depth estimates.