Seamount in the context of Ontong Java Plateau

An islet (/ˈaɪlət/ EYE-lət) is generally a small island. Definitions vary and are not precise, but some suggest that an islet is a very small, often unnamed, island with little or no vegetation to support human habitation. It may be made of rock, sand and/or hard coral; may be permanent or tidal (i.e. surfaced reef or seamount); and may exist in the sea, lakes, rivers or any other sizeable bodies of water.

24°15′24″N 22°28′16″W / 24.25667°N 22.47111°W / 24.25667; -22.47111

Macaronesia (Portuguese: Macaronésia; Spanish: Macaronesia) is a collection of four volcanic archipelagos in the North Atlantic Ocean, off the coast of North Africa and Europe. Each archipelago is made up of a number of Atlantic oceanic islands, which were formed by seamounts on the ocean floor whose peaks have risen above the ocean's surface.

The Hawaiian–Emperor seamount chain is a mostly undersea mountain range in the Pacific Ocean that reaches above sea level in Hawaii. It is composed of the Hawaiian ridge, consisting of the islands of the Hawaiian chain northwest to Kure Atoll, and the Emperor Seamounts: together they form a vast underwater mountain region of islands and intervening seamounts, atolls, shallows, banks and reefs along a line trending southeast to northwest beneath the northern Pacific Ocean. The seamount chain, containing over 80 identified undersea volcanoes, stretches about 6,200 km (3,900 mi) from near the Aleutian Trench off the coast of the Kamchatka peninsula in the far northwest Pacific to the Kamaʻehuakanaloa Seamount (formerly Lōʻihi), the youngest volcano in the chain, which lies about 35 kilometres (22 mi) southeast of the Island of Hawaiʻi.

The Hawaiʻi hotspot is a volcanic hotspot located near the namesake Hawaiian Islands, in the northern Pacific Ocean. One of the best known and intensively studied hotspots in the world, the Hawaii plume is responsible for the creation of the Hawaiian–Emperor seamount chain, a 6,200-kilometer (3,900 mi) mostly undersea volcanic mountain range. Four of these volcanoes are active, two are dormant; more than 123 are extinct, most now preserved as atolls or seamounts. The chain extends from south of the island of Hawaiʻi to the edge of the Aleutian Trench, near the eastern coast of Russia.

While some volcanoes are created by geologic processes near tectonic plate convergence and subduction zones, the Hawaiʻi hotspot is located far from plate boundaries. The classic hotspot theory, first proposed in 1963 by John Tuzo Wilson, proposes that a single, fixed mantle plume builds volcanoes that are then cut off from their source by the movement of the Pacific plate. This causes less lava to erupt from these volcanoes and they eventually erode below sea level over millions of years. According to this theory, the nearly 60° bend where the Emperor and Hawaiian segments within the seamounts was caused by shift in the movement of the Pacific Plate. Studies on tectonic movement have shown that several plates have changed their direction of plate movement because of differential subduction rates, breaking off of suducting slabs, and drag forces. In 2003, new investigations of this irregularity led to the proposal of a mobile hotspot hypothesis, suggesting that hotspots are prone to movement instead of the previous idea that hotspots are fixed in place, and that the 47-million-year-old bend was caused by a shift in the hotspot's motion rather than the plate's. According to this 2003 study, this could occur through plume drag taking parts of the plume in the direction of plate movement while the main plume could remain stationary. Many other hot spot tracks move in almost parallel so current thinking is a combination of these ideas.

The South China Sea Islands consist of over 250 islands, atolls, cays, shoals, reefs, and seamounts in the South China Sea. The islands are mostly low and small and have few inhabitants. The islands and surrounding seas are subject to overlapping territorial claims by the countries bordering the South China Sea.

The South China Sea Islands constitute a distinct tropical moist broadleaf forest terrestrial ecoregion and the South China Sea Oceanic Islands marine ecoregion.

An ocean bank, sometimes referred to as a fishing bank or simply bank, is a part of the seabed that is shallow compared to its surrounding area, such as a shoal or the top of an underwater hill. Somewhat like continental slopes, ocean bank slopes can upwell as tidal and other flows intercept them, sometimes resulting in nutrient-rich currents. Because of this, some large banks, such as Dogger Bank and the Grand Banks of Newfoundland, are among the richest fishing grounds in the world.

There are some banks that were reported in the 19th century by navigators, such as Wachusett Reef, whose existence is doubtful.

Demersal fish, also known as groundfish, live and feed on or near the bottom of seas or lakes (the demersal zone). They occupy the sea floors and lake beds, which usually consist of mud, sand, gravel or rocks. In coastal waters, they are found on or near the continental shelf, and in deep waters, they are found on or near the continental slope or along the continental rise. They are not generally found in the deepest waters, such as abyssal depths or on the abyssal plain, but they can be found around seamounts and islands. The word demersal comes from the Latin demergere, which means to sink.

Demersal fish are bottom feeders. They can be contrasted with pelagic fish, which live and feed away from the bottom in the open water column.Demersal fish fillets contain little fish oil (one to four per cent), whereas pelagic fish can contain up to 30 per cent.

This is a list of islands in the Atlantic Ocean, the largest of which is Greenland. Note that the definition of the ocean used by the International Hydrographic Organization (IHO) excludes the seas, gulfs, bays, etc., bordering the ocean itself. Thus, for instance, not all of the islands of the United Kingdom are actually in or bordering on the Atlantic. For reference, islands in gulfs and seas are included in a separate section. Oceanic islands are formed by seamounts rising from the ocean floor with peaks above the surface of the ocean and are not parts of continental tectonic plates.

The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru–Chile Trench, of the Nazca plate under the South American plate is largely responsible for the Andean orogeny. The Nazca plate is bounded on the west by the Pacific plate and to the south by the Antarctic plate through the East Pacific Rise and the Chile Rise, respectively. The movement of the Nazca plate over several hotspots has created some volcanic islands as well as east–west running seamount chains that subduct under South America. Nazca is a relatively young plate in terms of the age of its rocks and its existence as an independent plate, having been formed from the breakup of the Farallon plate about 23 million years ago. The oldest rocks of the plate are about 50 million years old.

Submarine navigation underwater requires special skills and technologies not needed by surface ships. The challenges of underwater navigation have become more important as submarines spend more time underwater, travelling greater distances and at higher speed. Military submarines travel underwater in an environment of total darkness with neither windows nor lights. Operating in stealth mode, they cannot use their active sonar systems to ping ahead for underwater hazards such as undersea mountains, drilling rigs or other submarines. Surfacing to obtain navigational fixes is precluded by pervasive anti-submarine warfare detection systems such as radar and satellite surveillance. Antenna masts and antenna-equipped periscopes can be raised to obtain navigational signals but in areas of heavy surveillance, only for a few seconds or minutes; current radar technology can detect even a slender periscope while submarine shadows may be plainly visible from the air.

Undersea mountain ranges are mountain ranges that are mostly or entirely underwater, and specifically under the surface of an ocean. If originated from current tectonic forces, they are often referred to as a mid-ocean ridge. In contrast, if formed by past above-water volcanism, they are known as a seamount chain. The largest and best known undersea mountain range is a mid-ocean ridge, the Mid-Atlantic Ridge. It has been observed that, "similar to those on land, the undersea mountain ranges are the loci of frequent volcanic and earthquake activity".

In geology, accretion is a process by which material is added to a tectonic plate at a subduction zone, frequently on the edge of existing continental landmasses. The added material may be sediment, volcanic arcs, seamounts, oceanic crust or other igneous features.

The Zhongsha Islands is a Chinese term for a collection of two skerries, many entirely submerged banks, seamounts, and shoals in the South China Sea. There are no islands in the Macclesfield Bank, the main part of Zhongsha. The Scarborough Shoal, which consists of two skerries, is not contiguous with the Macclesfield Bank, but Chinese sources treat them as one chain of geographical features. The whole of the region is claimed by both the PRC and the ROC, and various bits of the eastern parts are claimed by the Philippines. No country has constant control of the whole region, and there are disputes, such as the Scarborough Shoal standoff.

The PRC claims to administer the area as Zhongsha Daojiao Town (Chinese: 中沙岛礁镇; pinyin: Zhōngshā Dǎojiāo Zhèn), a town under the Xisha District of the Sansha prefecture-level city in Hainan. It has one Village-level division, Zhongsha Daojiao Residential Community. However, the seat of this town and residential community is not within the Zhongsha Islets, but on Woody Island.

The Patagonian toothfish (Dissostichus eleginoides), also known as Chilean sea bass and mero, is a species of notothen found in cold waters (1–4 °C or 34–39 °F) between depths of 45 and 3,850 m (150 and 12,630 ft) in the southern Atlantic, Pacific, and Indian Oceans and Southern Ocean on seamounts and continental shelves around most Subantarctic islands.

The average weight of a commercially caught Patagonian toothfish is 7–10 kg (15–22 lb), depending on the fishery, with large adults occasionally exceeding 100 kg (220 lb). They are thought to live up to 50 years and to reach a length up to 2.3 m (7.5 ft). Several commercial fisheries exist for Patagonian toothfish, which are detailed below.

The Louisville Ridge, often now referred to as the Louisville Seamount Chain, is an underwater chain of over 70 seamounts located in the Southwest portion of the Pacific Ocean. One of the longest seamount chains on Earth, it stretches some 4,300 km (2,700 mi) from the Pacific-Antarctic Ridge northwest to the Tonga-Kermadec Trench, where it subducts under the Indo-Australian Plate as part of the Pacific Plate. The chain's formation is best explained by movement of the Pacific Plate over the Louisville hotspot, although others have suggested that it formed by leakage of magma from the shallow mantle up through the Eltanin fracture zone, which it follows closely for some of its course.

Depth-sounding data first revealed existence consistent with a seamount chain in 1972, although some of the seamounts had been described as a ridge in 1964 linked to the Eltanin fracture zone system, hence the name.