The Pacific Ocean reaches its greatest depth in a long, arcing depression called the Mariana Trench. The trench's deepest point, known as Challenger Deep, has been measured at 35,840 feet — a depth of nearly seven miles! This depth is about a mile greater than the height above sea level of Mt. Everest, the world's highest peak. It is the deepest known point in any of the world's oceans.
The Mariana Trench lies east of the Mariana Islands in the western part of the Pacific Ocean. It is roughly 1,500 miles long, and it averages about 43 miles in width. (The trench is shown on the Indian and Pacific Oceans Floor Map. Open the PDF version of the map and then zoom in on the western Pacific Ocean.)
Like many other deep ocean trenches, the Mariana Trench follows the boundary between two of the earth's crustal plates: the Pacific Plate and the Philippine Plate. (These plates are shown on the World Plate Tectonics Map). Along this boundary, tectonic forces are slowly causing the Pacific Plate to slide beneath the Philippine Plate. This process is called subduction, and areas where it occurs are called subduction zones.
Scientists will soon have the chance to learn more about the Mariana Trench. The Woods Hole Oceanographic Institution (WHOI) in Massachusetts has developed a new undersea research vehicle named Nereus that is specifically designed for surveying and collecting samples from the greatest ocean depths. The WHOI, in cooperation with the National Oceanic and Atmospheric Administration, plans to send Nereus to explore Challenger Deep in late 2008 or early 2009.