The Tonga Trench is an oceanic trench located in the South Pacific Ocean. It is 10,882 metres (35,702 ft) deep at its deepest point, known as the Horizon Deep. According to the August 2011 version of the GEBCO Gazetteer of Undersea Feature Names, the location and depth of the Horizon Deep are given as and 10,800 m (35,433 ft) ±10 m (33 ft).
The Tonga Trench is a convergent plate boundary. The trench lies at the northern end of the Kermadec-Tonga Subduction Zone, an active subduction zone where the Pacific Plate is being subducted below the Tonga Plate and the Indo-Australian Plate. The Tonga Trench extends north-northeast from the Kermadec Islands north of the North Island of New Zealand. The trench turns west north of the Tonga Plate and becomes a transform fault zone.
The convergence is taking place at a rate estimated at approximately 15 centimetres (6 in) per year (by Lonsdale, 1986); however, recent global positioning satellite measurements indicate in places a convergence of 24 centimetres (9 in) per year across the northern Tonga Trench, which is the fastest plate velocity recorded on the planet; a result is the earth's most active zone of mantle seismicity. While most of the large earthquakes occur at the contact zone between both tectonic plates, related to the friction during subduction, others are produced in the Pacific plate due to its bending.
Such oceanic trenches are important sites for the formation of what will become continental crust and for recycling of material back into the mantle. Along the Tonga Trench mantle-derived melts are transferred to the island arc systems, and abyssal oceanic sediments and fragments of oceanic crust are collected.
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