12 octobre 2022
Definition of Seamount
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The most apparent lava flows on a seamount are the eruptive currents that cover its flanks, but magmatic intrusions in the form of dikes and thresholds are also an important part of seamount growth. The most common type of discharge is pillow lava, which thus bears its name after its distinctive shape. Less common are leaf currents, which are vitreous and marginal and indicate larger currents. Sedimentary rocks with volcanic elasticity dominate shallow-water seamounts. They are the products of the explosive activity of seamounts, which are located near the surface of the water, and can also form due to the mechanical wear of the existing volcanic rock. [11] Some seamounts have not been mapped and therefore pose a danger to navigation. For example, muirfield is named after the ship that struck it in 1973. [42] More recently, in 2005, the submarine USS San Francisco crashed into an unknown seamount at a speed of 35 knots (40.3 mph; 64.8 km/h), sustaining severe damage and killing a sailor. [41] Because of their abundance, seamounts are one of the most common marine ecosystems in the world. The interactions between seamounts and underwater currents, as well as their elevated position in the water, attract plankton, corals, fish and marine mammals.
Their overall effect has been noted by the commercial fishing industry, and many seamounts support extensive fishing. There is still concern about the negative impact of fishing on seamount ecosystems and well-documented cases of population decline, for example with Hoplostethus atlanticus (Hoplostethus atlanticus). 95% of ecological damage is caused by bottom trawling, which scrapes entire ecosystems from seamounts. Every country is starting to notice the impact of fishing on seamounts, and the European Commission has agreed to fund the OASIS project, a detailed study of the impact of fishing on seamount communities in the North Atlantic. [28] Another project engaged in nature conservation is CenSeam, a marine life counting project founded in 2005. CenSeam aims to provide the necessary framework to prioritize, integrate, expand and facilitate seamount research efforts to significantly reduce the unknown and build a comprehensive understanding of seamount ecosystems and the role they play in the biogeography, biodiversity, productivity and evolution of marine organisms. [29] [31] Earth`s oceans contain more than 14,500 identified seamounts,[3] of which 9,951 seamounts and 283 guyots with a total area of 8,796,150 km2 (3,396,210 square miles) have been mapped[4], but only a few have been studied in detail by scientists. Seamounts and guyots are the most common in the North Pacific and follow a distinctive evolutionary pattern of eruption, accumulation, subsidence and erosion.
In recent years, several active seamounts have been observed, for example Kamaʻehuakanaloa (formerly Lōʻihi) in the Hawaiian Islands. Before seamounts and their oceanographic effects can be fully understood, they must be mapped, a daunting task due to their numbers. [5] The most detailed mapping of seamounts is provided by multibeam echo sounders (sonar), but after more than 5,000 public cruises, the amount of mapped seabed remains tiny. Satellite altimetry is a more complete, if not as detailed, alternative, with 13,000 seamounts catalogued; However, this is still only a fraction of the total of 100,000. The reason for this is that uncertainties in the technology limit detection to characteristics of 1,500 m (4,921 ft) or more. In the future, technological advances could allow for a broader and more detailed catalogue. [23] Due to their large numbers, many seamounts still need to be properly studied and even mapped. Bathymetry and satellite altimetry are two technologies that bridge the gap.
There have been cases where warships have collided with unknown seamounts; For example, muirfield is named after the ship that struck it in 1973. However, the greatest danger of seamounts is the collapse of the flanks; As they age, extrusions that seep into seamounts exert pressure on their flanks, causing landslides that can create massive tsunamis. If all known seamounts were gathered in a single area, they would give a relief the size of Europe. [9] Their global abundance makes it one of the most common and least understood marine structures and biomes on Earth,[10] a kind of frontier for exploration. [11] Seamounts can form in a variety of tectonic environments, resulting in a very diverse structural bank. Seamounts come in various structural forms, ranging from the conical shape to the flat shape to the complex shape. [11] Some are very tall and very low, such as Koko Guyot[14] and Detroit Seamount; [15] Others are steeper, such as the Kamaʻehuakanaloa Seamount[16] and the Bowie Seamount. [17] Some seamounts also have a carbonate or sedimentary cap. [11] Seamount corals are also vulnerable, as they are highly valued for making jewelry and decorative objects. Significant harvests were obtained from seamounts, so the coral layers were often depleted. [5] New estimates suggest that seamounts together cover about 28.8 million square kilometers of the Earth`s surface.
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