Measuring the Greatest Ocean Depth
The Challenger Deep in the Mariana Trench is the deepest known point in Earth’s oceans. In 2010 the United States Center for Coastal & Ocean Mapping measured the depth of the Challenger Deep at 10,994 meters (36,070 feet) below sea level with an estimated vertical accuracy of ± 40 meters. If Mount Everest, the highest mountain on Earth, were placed at this location it would be covered by over one mile of water.
The first depth measurements in the Mariana Trench were made by the British survey ship HMS Challenger, which was used by the Royal Navy in 1875 to conduct research in the trench. The greatest depth that they recorded at that time was 8,184 meters (26,850 feet).
In 1951, another Royal Navy vessel, also named the “HMS Challenger”, returned to the area for additional measurements. They discovered an even deeper location with a depth of 10,900 meters (35,760 feet) determined by echo sounding. The Challenger Deep was named after the Royal Navy vessel.
In 2009, sonar mapping done by researchers aboard the RV Kilo Moana, operated by the University of Hawaii, determined the depth to be 10,971 meters (35,994 feet) with a potential error of ± 22 meters. The most recent measurement is the 10,994 meter ( ± 40 meter accuracy) depth reported above by the United States Center for Coastal & Ocean Mapping.
Map showing the geographic location of the Mariana Trench in the Pacific Ocean. Image from the CIA Factbook.
Exploring the Challenger Deep
The Challenger Deep was first explored by humans when Jacques Piccard and Don Walsh descended in the Trieste bathyscaphe in 1960. They reached a depth of 10,916 meters (35,814 feet).
In 2009 researchers from Woods Hole Oceanographic Institution completed the deepest dive by an unmanned robotic vehicle in the Challenger Deep. Their Nereus robotic vehicle reached a depth of 10,902 meters.
Map showing the location of the Challenger Deep on the southern end of the Mariana Trench, south of Guam.
Why is the ocean so deep here?
The Mariana Trench is located at a convergent plate boundary. Here two converging plates of oceanic lithosphere collide with one another. At this collision point, one of the plates descends into the mantle. At the line of contact between the two plates the downward flexure forms a trough known as an ocean trench. An example of an ocean trench is shown in the diagram below. Ocean trenches form some of the deepest locations in Earth’s oceans.