The New Britain Trench (also known as Bougainville-New Britain Trench or New Britain-Solomon Trench) [1] has formed due to subduction of the floor of the Solomon Sea and has some of the highest current seismic activity in the world. [2]
The trench was discovered by the German research vessel SMS Planet, in 1910. [3]
The trench is 840 km (520 mi) long, [2] curved around the south of New Britain and west of Bougainville Island in the northern Solomon Sea. The deepest point is the Planet Deep at 9,140 m (29,990 ft). [2]
The New Britain subduction zone is a continuum with the Vanuatu subduction zone and are all cases of subduction polarity reversal as originally the Pacific Plate subducted under the Indo-Australian Plate's minor plates such as the North Bismarck Plate. However now minor plate subduction is associated with the Australian Plate subducting under the Pacific Plate. In this case it is the Solomon Sea Plate and Trobriand Plate subducting under the South Bismarck Plate. [4] It is possible that the collision to the west of the 30–35 km (19–22 mi) thick Ontong Java Plateau with the Vitiaz Trench from about 25 million years ago initiated this polarity reversal. [5] The rates of subduction and roll back are high and are currently for the New Britain Trench, a subduction velocity of 65–120 cm/year (26–47 in/year), a convergence velocity of 2–48 cm/year (0.79–18.90 in/year), and spreading deformation rate in its arc-back- arc area of 10–74 cm/year (3.9–29.1 in/year). [6] In various parts of the trench there is up to 18 cm/year (7.1 in/year) of trench roll back and 20 cm/year (7.9 in/year) of trench advance. [6]
The New Britain subduction zone is extremely seismically active and has had more than 22 earthquakes with magnitudes equal to or larger than 7.5 since 1990. [7]
There is quite active arc volcanism with for example the active Rabaul Caldera area in the north east of New Britain having had a recent series of euptions in 1994 that destroyed the port of Rabaul. [8]
The diversity of life forms discovered living on top of the trench floor sediments and scavenging communities is high, [9] with during one study at 1 km (0.62 mi) depth 35 species observed, with biodiversity decreasing at 3.7 km (2.3 mi) depth before increasing again at 8.2 km (5.1 mi). [10] This is likely to reflect several factors. The trench is situated within the southern West Pacific Warm Pool characterized by sea surface temperature greater than 28°C and because of its closeness to tropical land, the land is subject to high rain fall. [11] The trench is only 55 km (34 mi) offshore from New Britain with an almost uniform slope into it of about 8°. [7] Hence there is a very high organic carbon load, sourced more than other trenches from soil organic matter, although marine phytoplankton and a minor contribution from land plants also help. [12]
Species observed at 1 km (0.62 mi) depth included a free swimming Teuthidodrilus (squidworm). [10] and ulmarid jellyfish.
At 8.7 km (5.4 mi) depth starfish and shrimps believed to be either of the family Penaeidae or the order Mysida were observed. [10] There were 5 amphipod species including Alicella gigantea. [13] Novel viruses and bacteria have been characterised in the sediment collected at this depth. [14] [15]
Oceanic trenches are prominent, long, narrow topographic depressions of the ocean floor. They are typically 50 to 100 kilometers wide and 3 to 4 km below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about 50,000 km (31,000 mi) of oceanic trenches worldwide, mostly around the Pacific Ocean, but also in the eastern Indian Ocean and a few other locations. The greatest ocean depth measured is in the Challenger Deep of the Mariana Trench, at a depth of 10,920 m (35,830 ft) below sea level.
Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year.
The Australian Plate is a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately 100 million years ago when India broke away and began moving north. Australia and Antarctica had begun rifting by 96 million years ago and completely separated a while after this, some believing as recently as 45 million years ago, but most accepting presently that this had occurred by 60 million years ago.
The Solomon Sea is a sea located within the Pacific Ocean. It lies between Papua New Guinea and Solomon Islands. Many major battles were fought there during World War II.
The Ontong Java Plateau (OJP) is a massive oceanic plateau located in the southwestern Pacific Ocean, north of the Solomon Islands. The OJP was formed around 116 million years ago (Ma), with a much smaller volcanic event around 90 Ma. Two other southwestern Pacific plateaus, Manihiki and Hikurangi, now separated from the OJP by Cretaceous oceanic basins, are of similar age and composition and probably formed as a single plateau and a contiguous large igneous province together with the OJP. When eruption of lava had finished, the Ontong Java–Manihiki–Hikurangi plateau covered 1% of Earth's surface and represented a volume of 80 million km3 (19 million cu mi) of basaltic magma. This "Ontong Java event", first proposed in 1991, represents the largest volcanic event of the past 200 million years, with a magma eruption rate estimated at up to 22 km3 (5.3 cu mi) per year over 3 million years, several times larger than the Deccan Traps. The smooth surface of the OJP is punctuated by seamounts such as the Ontong Java Atoll, one of the largest atolls in the world.
The Kermadec Trench is a linear ocean trench in the south Pacific Ocean. It stretches about 1,000 km (620 mi) from the Louisville Seamount Chain in the north (26°S) to the Hikurangi Plateau in the south (37°S), north-east of New Zealand's North Island. Together with the Tonga Trench to the north, it forms the 2,000 km (1,200 mi)-long, near-linear Kermadec-Tonga subduction system, which began to evolve in the Eocene when the Pacific Plate started to subduct beneath the Australian Plate. Convergence rates along this subduction system are among the fastest on Earth, 80 mm (3.1 in)/yr in the north and 45 mm (1.8 in)/yr in the south.
The Solomon Sea Plate is a minor tectonic plate to the northwest of the Solomon Islands archipelago in the south Pacific Ocean. It roughly corresponds with the Solomon Sea east of Papua New Guinea. The plate boundaries are associated with high earthquake activity as part of the New Britain subduction zone.
The Hikurangi Plateau is an oceanic plateau in the South Pacific Ocean east of the North Island of New Zealand. It is part of a large igneous province (LIP) together with Manihiki and Ontong Java, now located 3,000 km (1,900 mi) and 3,500 km (2,200 mi) north of Hikurangi respectively. Mount Hikurangi, in Māori mythology the first part of the North Island to emerge from the ocean, gave its name to the plateau.
The Caroline Plate is a minor tectonic plate that straddles the Equator in the eastern hemisphere located north of New Guinea. It forms a subduction zone along the border with the Bird's Head Plate and other minor plates of the New Guinea region to the south. A transform boundary forms the northern border with the Pacific Plate. Along the border with the Philippine Sea Plate is a convergent boundary that transitions into a rift.
The South Bismarck Plate is a small tectonic plate located mainly in the southern Bismarck Sea. The eastern part of New Guinea and the island of New Britain are on this plate. It is associated with high earthquake and volcanic activity as part of the New Britain subduction zone within the Pacific Ring of Fire.
The Woodlark Plate is a small almost triangular shaped tectonic plate located east of the island of New Guinea and situated mainly within the northern half of the Woodlark Basin. It is located in a very complex tectonic environment, that because of associated features, has been extensively studied since it was first proposed to exist. It is now known to be much smaller than originally proposed, mainly because of information from GPS stations on islands and sea floor studies that have fully defined its margins.
The West Melanesian Trench is an oceanic trench in the Bismarck Sea north of Papua New Guinea delineating the plate tectonic boundary between the Caroline and North Bismarck plates.
The Kilinailau Trench is an oceanic trench delineating the former oceanic crust boundary between the Pacific Plate and the now inactive North Bismarck Plate, in the area to the west of Papua New Guinea. To its south west is the inactive North Solomon Trench. The collision of the Ontong Java Plateau in the then subducting oceanic crust ot the Pacific Plate, initially to the trench's south-east, changed the plate collision dynamics relative to the then Indo-Australian Plate to the west. Now the Ontong Java Plateau is just to the east of the trench and its great depth of crust appears to explain why subduction stalled here, and moved to the opposite direction along the far side of New Britain and the Solomons. The Melanesian ocean arc ridge structures formed when the trench was active are to its west and would include the north eastern part of New Ireland.
The Woodlark Basin is a young geologic structural basin located in the southwestern Pacific Ocean, found to the southeast of the island country of Papua New Guinea. The basin is an extensional basin that is actively spreading and has a seafloor spreading center. The basin formed between the then Indo-Australian Plate and the Solomon microplate creating the presently independent Woodlark Plate. The Woodlark Basin has a complex geologic history dating back twenty million years to the initial opening of the basin but most of the spreading has happened in the last 3.6 million years.
The North Fiji Basin (NFB) is an oceanic basin west of Fiji in the south-west Pacific Ocean. It is an actively spreading back-arc basin delimited by the Fiji islands to the east, the inactive Vitiaz Trench to the north, the Vanuatu/New Hebrides island arc to the west, and the Hunter fracture zone to the south. Roughly triangular in shape with its apex located at the northern end of the New Hebrides Arc, the basin is actively spreading southward and is characterised by three spreading centres and an oceanic crust younger than 12 Ma. The opening of the NFB began when a slab roll-back was initiated beneath the New Hebrides and the island arc started its clockwise rotation. The opening of the basin was the result of the collision between the Ontong Java Plateau and the Australian Plate along the now inactive Solomon–Vitiaz subduction system north of the NFB. The NFB is the largest and most developed back-arc basin of the south-west Pacific. It is opening in a complex geological setting between two oppositely verging subduction systems, the New Hebrides/Vanuatu and Tonga trenches and hence its ocean floor has the World's largest amount of spreading centres per area.
The Tonga-Kermadec Ridge is an oceanic ridge in the south-west Pacific Ocean underlying the Tonga-Kermadec island arc. It is a result of the most linear, fastest converging, and seismically active subduction boundary on Earth, the Kermadec-Tonga subduction zone, and consequently has the highest density of submarine volcanoes.
The New Hebrides Trench is an oceanic trench which is over 7.1 km (4.4 mi) deep in the Southern Pacific Ocean. It lies to the northeast of New Caledonia and the Loyalty Islands, to the southwest of Vanuatu, east of Australia, and south of Papua New Guinea and the Solomon Islands. The trench was formed as a result of a subduction zone. The Australian Plate is being subducted under the New Hebrides Plate causing volcanism which produced the Vanuatu archipelago.
The Trobriand Plate was, and likely is, an independent microplate between New Guinea and the Solomon Islands. It has some unique geology, having the presence of the youngest metamorphic core complexes on earth. If there is presently active subduction between it and the Solomon Plate, at the Trobriand Trough, it continues to be an active microplate. Otherwise in the latest tectonic models it has merged with the Solomon Sea Plate, which becomes somewhat larger that predicted by Bird's 2003 model of Tectonic Plates. As a smaller Solomon Sea Plate is totally underwater, global positioning data can not resolve this issue. The area of the plate is associated with earthquake and volcanic activity as part of the Pacific Ring of Fire.
The New Britain subduction zone is one of the most recently formed and most active subduction zones on earth, producing great earthquakes, with potential for tsunami hazard, and being associated with active volcanism, as part of the Pacific Ring of Fire. It has a close relationship to an area of subduction tectonic activity that extends south eastward from New Britain to the Vanuatu subduction zone, involving the north eastern portion of the Australian Plate and its complicated collision dynamics with the south-western portion of the Pacific Plate.
The Hunter Ridge, is an active volcanic arc oceanic ridge located on the oceanic New Hebrides Plate in the south-west Pacific Ocean extending at least 550 km (340 mi). It defines the south-western limit of the North Fiji Basin (NFB) and is an area of unique range in volcanic geochemistry, which transpires to have been due partially to a new, previously unrecognised, subduction zone.
