The Mariana Trench is the deepest point on Earth, a colossal chasm in the ocean floor. Its magnitude has inspired decades of exploration, yet the trench remains one of the planet’s least understood features. The powerful geological forces that created this depth continue to reshape its contours. This raises the central question of whether this submarine valley is slowly getting deeper.
Defining the Maximum Depth
This immense feature is located in the western Pacific Ocean, running for about 1,580 miles east of the Mariana Islands. The deepest measured point within this crescent-shaped depression is the Challenger Deep, located at the trench’s southern end. Current consensus measurements place its maximum depth at approximately 10,984 meters (36,037 feet) below sea level.
To grasp this scale, consider Mount Everest, which stands at about 8,848 meters. If Mount Everest were placed at the bottom of the Challenger Deep, its summit would still be submerged more than a mile below the ocean’s surface. The pressure at this depth is over 1,000 times greater than the standard atmospheric pressure at sea level.
The Geological Engine of Subduction
The trench owes its existence and depth to the continuous collision of tectonic plates. It sits on a convergent plate boundary where the enormous Pacific Plate is forced beneath the smaller Mariana Plate. This geological process, known as subduction, is the engine that defines the trench’s depth.
The Pacific Plate is older, colder, and denser than the overriding Mariana Plate, causing it to bend and sink into the Earth’s mantle. This downward flexure creates the V-shaped depression of the trench. The subduction process is active, with the Pacific Plate converging beneath the Mariana Plate at a rate of approximately 5 centimeters per year.
This slow collision constantly acts as a downward pull, working to deepen the trench. The process also drives the formation of the volcanic Mariana Islands on the overriding plate. The trench is a direct result of this ongoing geological activity, which has been shaping the region for over 50 million years.
Current Evidence of Depth Change
The Mariana Trench is experiencing minute, constant change, though the net depth remains relatively stable over short human timescales. The main force for deepening is the continuous subduction of the Pacific Plate into the mantle. This slow, steady descent of the oceanic crust perpetually pulls the trench floor downward.
Opposing this deepening are two primary forces: sediment fill and tectonic uplift. Sediment, composed of fine pelagic clay and biological material, constantly accumulates on the trench floor, acting to make it shallower. However, the Mariana Trench is classified as a non-accretionary margin. This means nearly all the sediment that reaches the trench is scraped off and subducted into the mantle along with the descending Pacific Plate.
The depth has been determined through multiple historical surveys, first using weighted ropes in 1875, and later with modern acoustic mapping technology. Multibeam echosounders map the seafloor by measuring the time it takes for sound pulses to reflect off the bottom. Differences in reported depth between expeditions are often attributed to minor variations in acoustic mapping methods and the calculated speed of sound through the water column, not large-scale geological change.
The scientific consensus is that the net rate of change—the difference between deepening by subduction and shallowing by sediment and minor tectonic shifts—is extremely slow. While the trench is geologically dynamic, the overall depth changes are practically immeasurable over a span of decades. The immense depth is maintained by the balance of these opposing forces acting over millions of years.