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An underwater explosion (also known as an UNDEX) is a
chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., w ...
or
nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: *Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics *Nuclear space *Nuclear ...
explosion that occurs under the surface of a body of water. While useful in anti-ship and submarine warfare, underwater bombs are not as effective against coastal facilities.


Properties of water

Underwater explosions differ from in-air explosions due to the properties of
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
: *Mass and incompressibility (all explosions) – water has a much higher
density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...
than air, which makes water harder to move (higher
inertia Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law ...
). It is also relatively hard to compress (increase density) when under pressure in a low range (up to about 100 atmospheres). These two together make water an excellent conductor of
shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...
s from an
explosion An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known ...
. *Effect of neutron exposure on salt water (nuclear explosions only) – most underwater blast scenarios happen in
seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...
, not fresh or pure water. The water itself is not much affected by neutrons but salt is strongly affected. When exposed to neutron radiation during the microsecond of active detonation of a nuclear pit, water itself does not typically " activate", or become radioactive. The two elements in water,
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
and
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
, can absorb an extra neutron, becoming
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one ...
and oxygen-17 respectively, both of which are stable
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass num ...
s. Even oxygen-18 is stable. Radioactive atoms can result if a hydrogen atom absorbs two
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...
s, an oxygen atom absorbs three neutrons, or oxygen-16 undergoes a high energy neutron
(n-p) reaction The (n-p) reaction, or (n,p) reaction, is an example of a nuclear reaction. It is the reaction which occurs when a neutron enters a nucleus and a proton leaves the nucleus simultaneously. For example, sulfur-32 (32S) undergoes an (n,p) nuclear rea ...
to produce a short-lived nitrogen-16. In any typical scenario, the probability of such multiple captures in significant numbers in the short time of active nuclear reactions around a bomb is very low. They are somewhat greater when the water is continuously irradiated, as in the closed-loop primary cooling system of a
nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...
. However, salt in seawater readily absorbs neutrons into both the sodium-23 and
chlorine-35 Chlorine (17Cl) has 25 isotopes with mass numbers ranging from 28Cl to 52Cl and 2 isomers (34mCl and 38mCl). There are two stable isotopes, 35Cl (75.77%) and 37Cl (24.23%), giving chlorine a standard atomic weight of 35.45. The longest-lived rad ...
atoms, which change to radioactive isotopes. Sodium-24 has a
half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...
of about 15 hours, while that of
chlorine-36 Chlorine-36 (36Cl) is an isotope of chlorine. Chlorine has two stable isotopes and one naturally occurring radioactive isotope, the cosmogenic isotope 36Cl. Its half-life is 301,300 ± 1,500 years. 36Cl decays primarily (98%) by beta-minus deca ...
(which has a lower activation cross-section) is 300,000 years. The sodium is the most dangerous contaminant after the explosion because it has a short half-life. These are generally the main radioactive contaminants in an underwater blast; others are the usual blend of irradiated minerals,
coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...
, unused nuclear fuel, and bomb case components present in a surface blast
nuclear fallout Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refers to the radioac ...
, carried in suspension or dissolved in the water. Plain distillation or evaporating water (clouds, humidity, and precipitation) removes radiation contamination, leaving behind the radioactive salts.


Effects

Effects of an underwater
explosion An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known ...
depend on several things, including distance from the explosion, the energy of the explosion, the depth of the explosion, and the depth of the water. Underwater explosions are categorized by the depth of the explosion. Shallow underwater explosions are those where a
crater Crater may refer to: Landforms * Impact crater, a depression caused by two celestial bodies impacting each other, such as a meteorite hitting a planet * Explosion crater, a hole formed in the ground produced by an explosion near or below the surf ...
formed at the water's surface is large in comparison with the depth of the explosion. Deep underwater explosions are those where the crater is small in comparison with the depth of the explosion, or nonexistent. The overall effect of an underwater explosion depends on depth, the size and nature of the explosive charge, and the presence, composition and distance of reflecting surfaces such as the seabed, surface, thermoclines, etc. This phenomenon has been extensively used in antiship warhead design since an underwater explosion (particularly one underneath a hull) can produce greater damage than an above-surface one of the same explosive size. Initial damage to a target will be caused by the first
shockwave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a med ...
; this damage will be amplified by the subsequent physical movement of water and by the repeated secondary shockwaves or bubble pulse. Additionally, charge detonation away from the target can result in damage over a larger hull area. Underwater nuclear tests close to the surface can disperse radioactive water and steam over a large area, with severe effects on marine life, nearby infrastructures and humans. The detonation of nuclear weapons underwater was banned by the 1963
Partial Nuclear Test Ban Treaty The Partial Test Ban Treaty (PTBT) is the abbreviated name of the 1963 Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water, which prohibited all test detonations of nuclear weapons except for those conducted ...
and it is also prohibited under the
Comprehensive Nuclear-Test-Ban Treaty The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a multilateral treaty to ban nuclear weapons test explosions and any other nuclear explosions, for both civilian and military purposes, in all environments. It was adopted by the United Nati ...
of 1996.


Shallow underwater explosion

The Baker nuclear test at
Bikini Atoll Bikini Atoll ( or ; Marshallese: , , meaning "coconut place"), sometimes known as Eschscholtz Atoll between the 1800s and 1946 is a coral reef in the Marshall Islands consisting of 23 islands surrounding a central lagoon. After the Seco ...
in July 1946 was a shallow underwater explosion, part of
Operation Crossroads Operation Crossroads was a pair of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. They were the first nuclear weapon tests since Trinity in July 1945, and the first detonations of nuclear devices since the ...
. A 20
kiloton TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. The is a unit of energy defined by that convention to be , which is the approximate energy released in the detonation of a ...
warhead was detonated in a
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into '' coastal lagoons'' (or ''barrier lagoons ...
which was approximately deep. The first effect was illumination of the sea from the underwater fireball. A rapidly expanding gas bubble created a
shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...
that caused an expanding ring of apparently dark water at the surface, called the ''slick'', followed by an expanding ring of apparently white water, called the ''crack''. A mound of water and spray, called the ''spray dome'', formed at the water's surface which became more columnar as it rose. When the rising gas bubble broke the surface, it created a shock wave in the air as well. Water vapor in the air condensed as a result of Prandtl–Meyer expansion fans decreasing the air pressure, density, and temperature below the dew point; making a spherical cloud that marked the location of the shock wave. Water filling the cavity formed by the bubble caused a hollow column of water, called the ''chimney'' or ''plume'', to rise in the air and break through the top of the cloud. A series of ocean
surface wave In physics, a surface wave is a mechanical wave that propagates along the interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occur within liquids, at ...
s moved outward from the center. The first wave was about high at from the center. Other waves followed, and at further distances some of these were higher than the first wave. For example, at from the center, the ninth wave was the highest at . Gravity caused the column to fall to the surface and caused a cloud of mist to move outward rapidly from the base of the column, called the ''base surge''. The ultimate size of the base surge was in diameter and high. The base surge rose from the surface and merged with other products of the explosion, to form clouds which produced moderate to heavy rainfall for nearly one hour.


Deep underwater explosion

An example of a deep underwater explosion is the Wahoo test, which was carried out in 1958 as part of
Operation Hardtack I Operation Hardtack I was a series of 35 nuclear tests conducted by the United States from April 28 to August 18 in 1958 at the Pacific Proving Grounds. At the time of testing, the Operation Hardtack I test series included more nuclear detonatio ...
. A 9 kt Mk-7 was detonated at a depth of in deep water. There was little evidence of a fireball. The spray dome rose to a height of . Gas from the bubble broke through the spray dome to form jets which shot out in all directions and reached heights of up to . The base surge at its maximum size was in diameter and high. The heights of surface waves generated by deep underwater explosions are greater because more energy is delivered to the water. During the
Cold War The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because t ...
, underwater explosions were thought to operate under the same principles as tsunamis, potentially increasing dramatically in height as they move over shallow water, and flooding the land beyond the shoreline. Later research and analysis suggested that water waves generated by explosions were different from those generated by tsunamis and landslides. Méhauté ''et al.'' conclude in their 1996 overview ''Water Waves Generated by Underwater Explosion'' that the surface waves from even a very large offshore undersea explosion would expend most of their energy on the continental shelf, resulting in
coastal flooding Coastal flooding normally occurs when dry and low-lying land is submerged by seawater. The range of a coastal flooding is a result of the elevation of floodwater that penetrates the inland which is controlled by the topography of the coastal land ...
no worse than that from a bad storm. The
Operation Wigwam Operation Wigwam involved a single test of the Mark 90 "Betty" nuclear bomb. It was conducted between '' Operation Teapot'' and '' Project 56'' on May 14, 1955, about 500 miles (800 km) southwest of San Diego, California. 6,800 personne ...
test in 1955 occurred at a depth of , the deepest detonation of any nuclear device.


Deep nuclear explosion

Unless it breaks the water surface while still a hot gas bubble, an underwater nuclear explosion leaves no trace at the surface but hot, radioactive water rising from below. This is always the case with explosions deeper than about . About one second after such an explosion, the hot gas bubble collapses because: *The water pressure is enormous below . *The expansion reduces gas pressure, which decreases temperature. *
Rayleigh–Taylor instability The Rayleigh–Taylor instability, or RT instability (after Lord Rayleigh and G. I. Taylor), is an instability of an interface between two fluids of different densities which occurs when the lighter fluid is pushing the heavier fluid. Drazin ( ...
at the gas/water boundary causes "fingers" of water to extend into the bubble, increasing the boundary surface area. *Water is nearly incompressible. *Vast amounts of energy are absorbed by phase change (water becomes steam at the fireball boundary). *Expansion quickly becomes unsustainable because the amount of water pushed outward increases with the ''cube'' of the blast-bubble radius. Since water is not readily compressible, moving this much of it out of the way so quickly absorbs a massive amount of energy—all of which comes from the pressure inside the expanding bubble. Water pressure outside the bubble soon causes it to collapse back into a small sphere and rebound, expanding again. This is repeated several times, but each rebound contains only about 40% of the energy of the previous cycle. At the maximum diameter of the first oscillation, a very large nuclear bomb exploded in very deep water creates a bubble about a half-mile (800 m) wide in about one second and then contracts, which also takes about a second. Blast bubbles from deep nuclear explosions have slightly longer oscillations than shallow ones. They stop oscillating and become mere hot water in about six seconds. This happens sooner in nuclear blasts than bubbles from conventional explosives. The water pressure of a deep explosion prevents any bubbles from surviving to float up to the surface. The drastic 60% loss of energy between oscillation cycles is caused in part by the extreme force of a nuclear explosion pushing the bubble wall outward supersonically (faster than the speed of sound in saltwater). This causes
Rayleigh–Taylor instability The Rayleigh–Taylor instability, or RT instability (after Lord Rayleigh and G. I. Taylor), is an instability of an interface between two fluids of different densities which occurs when the lighter fluid is pushing the heavier fluid. Drazin ( ...
. That is, the smooth water wall touching the blast face becomes turbulent and fractal, with fingers and branches of cold ocean water extending into the bubble. That cold water cools the hot gas inside and causes it to condense. The bubble becomes less of a sphere and looks more like the
Crab Nebula The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus. The common name comes from William Parsons, 3rd Earl of Rosse, who observed the object in 1842 u ...
—the deviation of which from a smooth surface is also due to Rayleigh–Taylor instability as ejected stellar material pushes through the interstellar medium. As might be expected, large, shallow explosions expand faster than deep, small ones. Despite being in direct contact with a nuclear explosion fireball, the water in the expanding bubble wall does not boil; the pressure inside the bubble exceeds (by far) the vapor pressure of water. The water touching the blast can only boil during bubble contraction. This boiling is like evaporation, cooling the bubble wall, and is another reason that an oscillating blast bubble loses most of the energy it had in the previous cycle. During these hot gas oscillations, the bubble continually rises for the same reason a mushroom cloud does: it is less dense. This causes the blast bubble never to be perfectly spherical. Instead, the bottom of the bubble is flatter, and during contraction, it even tends to "reach up" toward the blast center. In the last expansion cycle, the bottom of the bubble touches the top before the sides have fully collapsed, and the bubble becomes a
torus In geometry, a torus (plural tori, colloquially donut or doughnut) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle. If the axis of revolution does n ...
in its last second of life. About six seconds after detonation, all that remains of a large, deep nuclear explosion is a column of hot water rising and cooling in the near-freezing ocean.


List of underwater nuclear tests

Relatively few underwater nuclear tests were performed before they were banned by the Partial Test Ban Treaty. They are: Note: it is often believed that the
French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...
did extensive underwater tests in French West Polynesia on the
Moruroa Moruroa (Mururoa, Mururura), also historically known as Aopuni, is an atoll which forms part of the Tuamotu Archipelago in French Polynesia in the southern Pacific Ocean. It is located about southeast of Tahiti. Administratively Moruroa Atoll i ...
and
Fangataufa Fangataufa (or Fangatafoa) is an uninhabited coral atoll in the eastern part of the Tuamotu Archipelago in French Polynesia. The atoll has been fully-owned by the French state since 1964. From 1966 to 1996 it was used as a nuclear test site by t ...
Atolls. This is incorrect; the bombs were placed in shafts drilled into the underlying coral and volcanic rock, and they did not intentionally leak fallout.


Nuclear Test Gallery

File:Operation Crossroads Baker.jpg, Crossroads Baker File:Op hurricane.jpg, Operation Hurricane File:Hardtack Umbrella nuke.jpg, Hardtack Umbrella File:Nuclear depth charge explodes near USS Agerholm (DD-826) on 11 May 1962.jpg, Dominic Swordfish


Underwater Nuclear Detonation Detection via Hydroacoustics

There are several methods of detecting nuclear detonations. Hydroacoustics is the primary means of determining if a nuclear detonation has occurred underwater. Hydrophones are used to monitor the change in water pressure as sound waves propagate through the world's oceans. Sound travels through 20 °C water at approximately 1482 meters per second, compared to the 332 m/s speed of sound through air. In the world's oceans, sound travels most efficiently at a depth of approximately 1000 meters. Sound waves that travel at this depth travel at minimum speed and are trapped in a layer known as the Sound Fixing and Ranging Channel ( SOFAR). Sounds can be detected in the SOFAR from large distances, allowing for a limited number of monitoring stations required to detect oceanic activity. Hydroacoustics was originally developed in the early 20th century as a means of detecting objects like icebergs and shoals to prevent accidents at sea. Three hydroacoustic stations were built before the adoption of the
Comprehensive Nuclear-Test-Ban Treaty The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a multilateral treaty to ban nuclear weapons test explosions and any other nuclear explosions, for both civilian and military purposes, in all environments. It was adopted by the United Nati ...
. Two hydrophone stations were built in the North Pacific Ocean and Mid-Atlantic Ocean, and a T-phase station was built off the west coast of Canada. When the CTBT was adopted, 8 more hydroacoustic stations were constructed to create a comprehensive network capable of identifying underwater nuclear detonations anywhere in the world. These 11 hydroacoustic stations, in addition to 326 monitoring stations and laboratories, comprise the
International Monitoring System The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization, or CTBTO Preparatory Commission, is an international organization based in Vienna, Austria, that is tasked with building up the verification regime of the Co ...
(IMS), which is monitored by the
Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization, or CTBTO Preparatory Commission, is an international organization based in Vienna, Austria, that is tasked with building up the verification regime of the Com ...
(CTBTO). There are two different types of hydroacoustic stations currently used in the IMS network; 6 hydrophone monitoring stations and 5 T-phase stations. These 11 stations are primarily located in the southern hemisphere, which is primarily ocean. Hydrophone monitoring stations consist of an array of three hydrophones suspended from cables tethered to the ocean floor. They are positioned at a depth located within the SOFAR in order to effectively gather readings. Each hydrophone records 250 samples per second, while the tethering cable supplies power and carries information to the shore. This information is converted to a usable form and transmitted via secure satellite link to other facilities for analysis. T-phase monitoring stations record seismic signals generate from sound waves that have coupled with the ocean floor or shoreline. T-phase stations are generally located on steep-sloped islands in order to gather the cleanest possible seismic readings. Like hydrophone stations, this information is sent to the shore and transmitted via satellite link for further analysis. Hydrophone stations have the benefit of gathering readings directly from the SOFAR, but are generally more expensive to implement than T-phase stations. Hydroacoustic stations monitor frequencies from 1 to 100 Hertz to determine if an underwater detonation has occurred. If a potential detonation has been identified by one or more stations, the gathered signals will contain a high bandwidth with the frequency spectrum indicating an underwater cavity at the source.


See also

*
Nuclear weapons testing Nuclear weapons tests are experiments carried out to determine nuclear weapons' effectiveness, yield, and explosive capability. Testing nuclear weapons offers practical information about how the weapons function, how detonations are affected by ...
* Marine engineering * Shock factor *
Nuclear depth bomb A nuclear depth bomb is the nuclear equivalent of the conventional depth charge, and can be used in anti-submarine warfare for attacking submerged submarines. The Royal Navy, Soviet Navy, and United States Navy had nuclear depth bombs in their ...
*
Nuclear torpedo A nuclear torpedo is a torpedo armed with a nuclear warhead. The idea behind the nuclear warheads in a torpedo was to create a much bigger explosive blast. Later analysis suggested that smaller, more accurate, and faster torpedoes were more effici ...
*
Operation Chastise Operation Chastise or commonly known as the Dambusters Raid was an attack on Nazi Germany, German dams carried out on the night of 16/17 May 1943 by No. 617 Squadron RAF, 617 Squadron RAF Bomber Command, later called the Dam Busters, using sp ...


Sources


Further reading

* *{{cite book , last1=Le Méhauté , first1=Bernard , last2=Wang , first2=Shen , title=Water waves generated by underwater explosion , publisher=World Scientific Publishing , year=1995 , isbn=981-02-2083-9 , volume=10 , series=Advanced Series on Ocean Engineering, url=https://apps.dtic.mil/sti/pdfs/ADA304244.pdf, archive-url=https://web.archive.org/web/20191014235430/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA304244, url-status=live, archive-date=October 14, 2019 Explosions Nuclear technology