The ocean floor near the margins of the Pacific, especially in its western portion, contains many elongated troughs, some of which are the deepest known on the earth. These deeps, or foredeeps, are parallel to mountain uplifts or to the platforms that support curving rows of islands, and apparently have resulted from the subsidence of the foreland beneath the folded mountains.
A deep, to be called such, must exceed 18,000 feet in depth. Important deeps include Kurile-Japanese ( Tuscarora Deep, 32,644 feet deep); Ryukyu (24,479 feet) east of the islands of that name and east of the Bonins ( RamapoDeep Deep, 34,626 feet); Philippine Trench east of north Mindanao ( Mindanao Deep has the greatest depth known in any ocean, 35,410 feet); deeps east of Palau (26,700 feet), east of Yap (24,732 feet), southeast of Guam ( Nero Deep, 32,177 feet), and between Wake and Midway ( Bailey Deep, 20,591 feet); Bougainville Trench south of New Britain ( Planet Deep, 30,865 feet); west of the New Hebrides (24,837 feet); and the Kermadec-Tonga Trench ( Aldrich Deep, 30,930 feet, and Tonga, 30,132 feet) between New Zealand and Samoa. In the north Pacific the greatest depth is found in the Aleutian Deep (25,194 feet), southwest of Attu; and in the southeast Pacific is the Atacama Trench (24,216 feet deep) off the coast of Peru and Chile. The combined areas of great depth in the Pacific are small. All the deeps are elongated and lie parallel either to present coasts and mountains or to the coasts of earlier continents that have largely sunk beneath the sea. The central floor of the Pacific is only about half as deep as the troughs around its margin.