The Tonga Trench is a submarine trench located in the floor of the South Pacific Ocean. It forms the eastern boundary of the Tonga Ridge. It's 35,702 feet deep at its deepest point and has an average depth of 20,000 feet. It's about 50 miles wide and 850 miles in length. The Tonga Trench and Tonga Ridge form the northern half of the Tonga-Kermadec Arc.
The Tonga Trench is a convergent plate boundary located where the Pacific Plate is being subducted below the Tonga Plate and the Indo-Australian Plate. The Tonga Trench reaches from a point between the Kermadec Islands to the north of New Zealand. The Australian Plate is considered to be younger and more buoyant and is causing the Pacific Plate to sink below it. The fastest plate motion ever recorded occurs at the northern end of the trench, at around 9 inches per year. The area is considered earth's most active zone of mantle seismicity. The contact zone between the two plates creates large earthquakes as a result of the friction created during subduction. Scientists expect new continental crusts to form eventually at the site of the Tonga Trench, as well as for material from the trench to be recycled back into the earth's mantle.