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Tonga Trench
submarine trench, South Pacific Ocean
Tonga Trench, submarine trench in the floor of the South Pacific Ocean, about 850 miles (1,375 km) in length, forming the eastern boundary of the Tonga Ridge; the two together constitute the northern half of the Tonga-Kermadec Arc, a structural feature of the Pacific floor completed to the south by the Kermadec Trench and Ridge. The Tonga Trench has an average depth of 20,000 feet (6,000 m) and a width of about 50 miles (80 km); it reaches a maximum depth of 35,702 feet (10,882 m).