MOSCOW, May 16, Vladislav Strekopytov. A detailed map of the bottom of the World Ocean is 25 percent ready, announced at the assembly of the International Hydrographic Organization in Monaco. Scientists, among other things, have identified the location of more than 19 thousand underwater volcanoes, which contain deposits of valuable metals, but pose a mortal danger to submarines.
Planet Ocean
The oceans cover about two-thirds of the planet, but experts often say that the surface of Mars is better studied than the seabed. And this is true. Seabed mapping is an expensive and technologically time-consuming procedure. However, its results are extremely in demand. Detailed bathymetric maps — analogues of land topographic maps — are necessary for safe maritime navigation, laying of submarine cables and pipelines, climate forecasts, and development of the resources of the World Ocean. Scientists use them in modeling ocean currents and tsunami waves, studying underwater ecosystems, in geological, geophysical and other studies.
The first very approximate physiographic map of the ocean was built in the 1950s. The survey of the underwater relief was carried out by the sonar method: the simplest single-beam echo sounder estimated the depth from the time of passage of the wave signal reflected from the seabed. Then, in the axial part of the Atlantic Ocean, a volcanic ridge was discovered, formed during the outpouring of lava at the place of separation of the lithospheric plates. This became one of the confirmations of the theory of continental drift.
In the 1970s, more efficient multi-beam sonar emitting a fan signal became available. Such devices were installed on research and some civil ships. This somewhat speeded up the process of studying the seabed, but it was still very long: the survey covered only a narrow strip along the ship's route. media-type=»photo» data-crop-ratio=»0.6″ data-crop-width=»600″ data-crop-height=»360″ data-source-sid=»cc_by_20″ class=»lazyload» width= «1920» height=»1152″ decoding=»async» />
Today, hydrographers have at their disposal a whole arsenal of technical means — from aircraft laser imaging devices (lidars) to remotely controlled underwater vehicles capable of diving to great depths. True, all of them perform auxiliary functions, and sonar still plays the main role.
Scientists have calculated that in order to conduct an areal survey of the entire ocean floor with a resolution of 100 meters, it will take tens of years and thousands of trips of specialized geophysical vessels equipped with hydroacoustic installations of the type sonar (from English sonar, abbr. SOund Navigation And Ranging).
Ambitious goals
By the mid-2010s, only 19 percent of the total ocean floor area had been mapped, and no more than six percent had been surveyed in detail. To remedy the situation, Japan's Nippon Foundation and intergovernmental non-profit ocean bathymetry organization GEBCO launched the Seabed 2030 (Seabed 2030) project in 2016.
The goal was to create by 2030 a comprehensive and publicly available map of the World Ocean based on the GEBCO global bathymetric grid. The initiators called on research institutes, government agencies and private companies to share hydrographic data.
Several governments have responded to this call. In addition, in 2017 the project received the status of a joint program of the International Hydrographic Organization (IHO) and the Intergovernmental Oceanographic Commission (IOC) of UNESCO. In the same year, the UN General Assembly declared the development of a comprehensive map of the ocean a key objective of the Decade of the Ocean (2021-2030).
Thanks to a global partnership, an additional 90 million square kilometers of bathymetric data have been mapped in the six years since the start of the project. Today, detailed surveys already cover 25 percent of the ocean floor. But three-quarters of the area remains a blank spot. The problems are related to technological limitations, especially when studying deep-sea areas, and the high cost of cartographic expeditions.
As conceived by the organizers, the main source of information should be hundreds of thousands of ships of various purposes (from giant container ships to fishing boats and private yachts) equipped with onboard echo sounders. Experts have calculated that if at least 200 ships are constantly working in the project, the goal will be achieved on time.
«Everyone who is connected with the ocean can play an important role in mapping the entire seabed before the end of the decade,» the report says. Statement of the Assembly of the International Hydrographic Organization.
Submarine Assassins
Remote sensing methods could significantly speed up the process of mapping the seabed. But space-based scanners and radars, which are successfully used to make detailed maps of the land, are unable to penetrate the water column.
In recent years, satellite radiometry, based on tracking small local changes in sea level . Scientists have found that it is slightly higher over ridges and seamounts than over depressions and abyssal plains. This difference, called the vertical gravity gradient (VGG), indirectly reflects bottom roughness.
Satellite altimetry based on SHG significantly outperforms sonar in terms of performance, but is not suitable for areal surveys, since it detects only objects several kilometers high. Nevertheless, it has been successfully used to map large seamounts that pose a serious danger to submarines.
There are at least two known cases of US submarines colliding with similar objects. In October 2021, the nuclear submarine USS Connecticut in the South China Sea crashed into an uncharted mountain at a depth of about 400 meters. The nuclear reactor was not damaged, but several crew members were injured. 
In January 2005, the attack submarine USS San Francisco hit an underwater peak while moving at a depth of about 160 meters off Guam Island in the Pacific Ocean.
Satellite data is also used to search for minerals at the bottom of the sea — the slopes of underwater ridges often contain significant reserves of polymetals, manganese, cobalt and rare earth elements. jpg» media-type=»photo» data-crop-ratio=»0.790833333333333″ data-crop-width=»600″ data-crop-height=»474″ data-source-sid=»afp» class=»lazyload» width=»1920″ height=»1518″ decoding=»async» />
Thousands of New Volcanoes
Recently, US and South Korean scientists, led by Julie Gevorgian of the Scripps Oceanographic Institution in California, have developed an algorithm to improve the accuracy of satellite observations. As initial data, we took the observations of CryoSat-2 of the European Space Agency and SARAL, a joint altimetry mission of the Indian Space Research Organization (ISRO) and the National Center for Space Research of France (CNES).
This approach helped identify 19,325 previously unknown underwater volcanoes. The smallest of them is only 421 meters high, and most are from 700 to 2500 meters. Prior to this, there were 24,643 objects in the global catalog of seamounts. Now their number has almost doubled. In total, according to researchers, there may be about 55,000 underwater peaks above 2500 meters in the world.
A new algorithm for processing satellite data makes it possible to detect even smaller forms of underwater relief with an accuracy of up to 270 meters. And also to draw up IGG maps that are not inferior in accuracy to the results of sonar observations. 
The authors hope that in the near future such maps will become the basis for many scientific constructions.