Underground nuclear testing Underground nuclear testing refers to test detonations of nuclear weapon s that are performed underground . When the device being tested is buried at sufficient depth , the explosion may be contained , with no release of radioactive material s to the atmosphere . The extreme heat and pressure of an underground nuclear explosion causes changes in the surrounding rock . The rock closest to the location of the test is vaporised , forming a cavity . Farther away , there are zones of crushed , cracked , and irreversibly strained rock . Following the explosion , the rock above the cavity may collapse , forming a rubble chimney . If this chimney reaches the surface , a bowl - shaped subsidence crater may form . The first underground test took place in 1951 ; further tests provided information that eventually led to the signing of the Limited Test Ban Treaty in 1963 , which banned all nuclear tests except for those performed underground . From then until the signing of the Comprehensive Test Ban Treaty in 1996 , most nuclear tests were performed underground , in order to prevent nuclear fallout from entering into the atmosphere . Background . Although public concern about fallout from nuclear testing grew in the early 1950s , fallout was discovered after the Trinity test in 1945 . Photographic film manufacturers would later report ' fogged ' films , these were traced both to " Trinity " and later tests at the Nevada Test Site . Intense fallout from the 1953 " Simon " test was documented as far as Albany , New York . The fallout from the March 1954 " Bravo " test in the Pacific would have " scientific , political and social implications that have continued for more than 40 years . " The multi - megaton test caused fallout to occur on the islands of Rongerik and Rongelap , and a Japan ese fishing boat known as the " Daigo Fukuryū Maru " ( Lucky Dragon ) . Prior to this test , there was " insufficient " appreciation of the dangers of fallout . The test became an international incident . In a PBS interview , the historian Martha Smith argued : " In Japan , it becomes a huge issue in terms of not just the government and its protest against the United States , but all different groups and all different peoples in Japan start to protest . It becomes a big issue in the media . There are all kinds of letters and protests that come from , not surprisingly , Japanese fishermen , the fishermen ' s wives ; there are student groups , all different types of people ; that protest against the Americans ' use of the Pacific for nuclear testing . They ' re very concerned about , first of all , why the United States even has the right to be carrying out those kinds of tests in the Pacific . They ' re also concerned about the health and environmental impact . " The Prime Minister of India " voiced the heightened international concern " when he called for the elimination of all nuclear testing worldwide . Knowledge about fallout and its effects grew , and with it concern about the global environment and long - term genetic damage . Talks between the United States , the United Kingdom , Canada , France , and the Soviet Union began in May 1955 on the subject of an international agreement to end nuclear tests . On August 5 , 1963 , representatives of the United States , the Soviet Union , and the United Kingdom signed the Limited Test Ban Treaty , forbidding testing of nuclear weapons in the atmosphere , in space , and underwater . Agreement was facilitated by the decision to allow underground testing , eliminating the need for on - site inspections that concerned the Soviets . Underground testing was allowed , provided that it does not cause " radioactive debris to be present outside the territorial limits of the State under whose jurisdiction or control such explosion is conducted . " Early history of underground testing . Following analysis of underwater detonations that were part of Operation Crossroads in 1946 , inquiries were made regarding the possible military value of an underground explosion . The Joint Chiefs of Staff thus obtained the agreement of the Atomic Energy Commission to perform experiments on both surface and sub - surface detonations . The island of Amchitka was initially selected for these tests in 1950 , but the site was later deemed unsuitable and the tests were moved to the Nevada Test Site . The first underground nuclear test was conducted on 29 November 1951 . This was the 1 . 2 kiloton " Buster - Jangle Uncle " , which detonated 5 . 2 m ( 17 ft ) beneath ground level . The test was designed as a scaled - down investigation of the effects of a 23 kiloton ground penetrating gun - type device that was then being considered for use as a cratering and bunker - buster weapon . The explosion resulted in a cloud that rose to 11 , 500 ft , and deposited fallout to the north and north - northeast . The resulting crater was 260 feet wide and 53 feet deep . The next underground test was " Teapot Ess " , on 23 March 1955 . The 1 kiloton explosion was an operational test of an atomic demolition munition ( ADM ) . It was detonated 67 feet underground , in a shaft lined with corrugated steel , which was then back - filled with sandbags and dirt . Because the ADM was buried underground , the explosion blew tons of earth upwards , creating a crater 300 feet wide and 128 feet deep . The resulting mushroom cloud rose to a height of 12 , 000 feet and subsequent radioactive fallout drifted in an easterly direction , travelling as far as from ground zero . On 26 July 1957 , " Plumbbob Pascal - A " was detonated at the bottom of a 485 - foot shaft . According to one description , it " ushered in the era of underground testing with a magnificent pyrotechnic Roman candle ! " As compared with an above - ground test , the radioactive debris released to the atmosphere was reduced by a factor of ten . Theoretical work began on possible containment schemes . " Plumbbob Rainier " was detonated at 899 ft underground on 19 September 1957 . The 1 . 7 kt explosion was the first to be entirely contained underground , producing no fallout . The test took place in a 1 , 600 – 2 , 000 ft horizontal tunnel in the shape of a hook . The hook " was designed so explosive force will seal off the non - curved portion of tunnel nearest the detonation before gases and fission fragments can be vented around the curve of the tunnel ' s hook . " This test would become the prototype for larger , more powerful tests . Rainier was announced in advance , so that seismic stations could attempt to record a signal . Analysis of samples collected after the test enabled scientists to develop an understanding of underground explosions that " persists essentially unaltered today . " The information would later provide a basis for subsequent decisions to agree to the Limited Test Ban Treaty . " Cannikin " , the last test at the Amchitka facility was detonated on 6 November 1971 . At approximately 5 megatons , it was the largest underground test in US history . Effects . The effects of an underground nuclear test may vary according to factors including the depth and yield of the explosion , as well as the nature of the surrounding rock . If the test is conducted at sufficient depth , the test is said to be " contained " , with no venting of gases or other contaminants to the environment . In contrast , if the device is buried at insufficient depth ( " underburied " ) , then rock may be expelled by the explosion , forming a crater surrounded by ejecta , and releasing high - pressure gases to the atmosphere ( the resulting crater is usually conical in profile , circular , and may range between tens to hundreds of metres in diameter and depth ) . One figure used in determining how deeply the device should be buried is the " scaled depth of burial " , or " - burst " . This figure is calculated as the burial depth in metres divided by the cube root of the yield in kilotons . It is estimated that , in order to ensure containment , this figure should be greater than 100 . The energy of the nuclear explosion is released in one microsecond . In the following few microseconds , the test hardware and surrounding rock are vaporised , with temperatures of several million degrees and pressures of several million atmospheres . Within milliseconds , a bubble of high - pressure gas and steam is formed . The heat and expanding shock wave cause the surrounding rock to vaporise , or be melted further away , creating a " melt cavity " . The shock - induced motion and high internal pressure cause this cavity to expand outwards , which continues over several tenths of a second until the pressure has fallen sufficiently , to a level roughly comparable with the weight of the rock above , and can no longer grow . Although not observed in every explosion , four distinct zones ( including the melt cavity ) have been described in the surrounding rock . The " crushed zone " , about two times the radius of the cavity , consists of rock that has lost all of its former integrity . The " cracked zone " , about three times the cavity radius , consists of rock with radial and concentric fissures . Finally , the " zone of irreversible strain " consists of rock deformed by the pressure . The following layer undergoes only an elastic deformation ; the strain and subsequent release then forms a seismic wave . A few seconds later the molten rock starts collecting on the bottom of the cavity and the cavity content begins cooling . The rebound after the shock wave causes compressive forces to build up around the cavity , called a stress containment cage , sealing the cracks . Several minutes to days later , once the heat dissipates enough , the steam condenses , and the pressure in the cavity falls below the level needed to support the overburden , the rock above the void falls into the cavity , creating a " rubble chimney " . Depending on various factors , including the yield and characteristics of the burial , this collapse may extend to the surface . If it does , a subsidence crater is created . Such a crater is usually bowl - shaped , and ranges in size from a few tens of metres to over a kilometre in diameter . At the Nevada Test Site , 95 percent of tests conducted at a scaled depth of burial ( SDOB ) of less than 150 caused surface collapse , compared with about half of tests conducted at a SDOB of less than 180 . The radius " r " ( in feet ) of the cavity is proportional to the cube root of the yield " y " ( in kilotons ) , " r " = 55 * formula _ 1 ; a 8 kiloton explosion will create a cavity with radius of 110 feet . Other surface features may include disturbed ground , pressure ridge s , faults , water movement ( including changes to the water table level ) , rockfall s , and ground slump . Most of the gas in the cavity is composed of steam ; its volume decreases dramatically as the temperature falls and the steam condenses . There are however other gases , mostly carbon dioxide and hydrogen , which do not condense and remain gaseous . The carbon dioxide is produced by thermal decomposition of carbonate s , hydrogen is created by reaction of iron and other metals from the nuclear device and surrounding equipment . The amount of carbonates and water in the soil and the available iron have to be considered in evaluating the test site containment ; water - saturated clay soils may cause structural collapse and venting . Hard basement rock may reflect shock waves of the explosion , also possibly causing structural weakening and venting . The noncondensible gases may stay absorbed in the pores in the soil . Large amount of such gases can however maintain enough pressure to drive the fission products to the ground . Escape of radioactivity from the cavity is known as containment failure . Massive , prompt , uncontrolled releases of fission products , driven by the pressure of steam or gas , are known as venting ; an example of such failure is the Baneberry test . Slow , low - pressure uncontrolled releases of radioactivity are known as seeps ; these have little to no energy are not visible and have to be detected by instruments . Late - time seeps are releases of noncondensable gases days or weeks after the blast , by diffusion through pores and crack , probably assisted by a decrease of atmospheric pressure ( so called " atmospheric pumping " ) . When the test tunnel has to be accessed , controlled tunnel purging is performed ; the gases are filtered , diluted by air and released to atmosphere when the winds will disperse them over sparsely populated areas . Small activity leaks resulting from operational aspects of tests are called operational releases ; they may occur e . g . during drilling into the explosion location during core sampling , or during the sampling of explosion gases . The radionuclide composition differs by the type of releases ; large prompt venting releases significant fraction ( up to 10 % ) of fission products , while late - time seeps contain only the most volatile gases . Soil absorbs the reactive chemical compounds , so the only nuclides filtered through soil into the atmosphere are the noble gases , primarily krypton - 85 and xenon - 133 . The released nuclides can undergo bioaccumulation . Iodine - 131 , strontium - 90 and caesium - 137 are concentrated in milk of grazing cows ; cow milk is therefore a convenient , sensitive fallout indicator . Soft tissues of animals can be analyzed for gamma emitters , bones and liver for strontium and plutonium , and blood , urine and soft tissues are analyzed for tritium . Although there were early concerns about earthquakes arising as a result of underground tests , there is no evidence that this has occurred . However , fault movements and ground fractures have been reported , and explosions often precede a series of aftershock s , thought to be a result of cavity collapse and chimney formation . In a few cases , seismic energy released by fault movements has exceeded that of the explosion itself . International treaties . Signed in Moscow on August 5 , 1963 by representatives of the United States , the Soviet Union , and the United Kingdom , the Limited Test Ban Treaty agreed to ban nuclear testing in the atmosphere , in space , and underwater . Due to the Soviet government ' s concern about the need for the on - site inspections , underground tests were excluded from the ban . 108 countries would eventually sign the treaty , with the significant exceptions of France and China . In 1974 , the United States and the Soviet Union signed the Threshold Test Ban Treaty , which banned underground tests with yields greater than 150 kilotons . By the 1990s , technologies to monitor and detect underground tests had matured to the point that tests of one kiloton or over could be detected with high probability , and in 1996 negotiations began under the auspices of the United Nations to develop a comprehensive test ban . The resulting Comprehensive Nuclear - Test - Ban Treaty was signed in 1996 by the United States , Russia , United Kingdom , France , and China . However , following the United States Senate decision not to ratify the treaty in 1999 , it is still yet to be ratified by 8 of the required 44 ' Annex 2 ' states and so has not entered into force as United Nations law . Monitoring . In the late 1940s , the United States began to develop the capability to detect atmospheric testing using air sampling ; this system was able to detect the first Soviet test in 1949 . Over the next decade , this system was improved , and network of seismic monitoring stations was established to detect underground tests . Development of the Threshold Test Ban Treaty in the mid - 1970s led to an improved understanding of the relationship between test yield and resulting seismic magnitude . When negotiations began in the mid - 1990s to develop a comprehensive test ban , the international community was reluctant to rely upon the detection capabilities of individual nuclear weapons states ( especially the United States ) , and instead wanted an international detection system . The resulting International Monitoring System consists of a network of a total of 321 monitoring stations and 16 radionuclide laboratories . Fifty " primary " seismic stations send data continuously to the International Data Center , along with 120 " auxiliary " stations which send data on request . The resulting data is used to locate the epicentre , and distinguish between the seismic signatures of an underground nuclear explosion and an earthquake . Additionally , eighty radionuclide stations detect radioactive particles vented by underground explosions . Certain radionuclides constitute clear evidence of nuclear tests ; the presence of noble gases can indicate whether an underground explosion has taken place . Finally , eleven hydroacoustic stations and sixty infrasound stations monitor underwater and atmospheric tests .