page_title: Underground nuclear weapons testing
section_title: Early history of underground testing
hierarchical_section_title: Underground nuclear weapons testing / Early history of underground testing
caption_attribution_description: English: The Buster-Jangle Uncle nuclear test.
context_page_description: Underground nuclear testing is the test detonation of nuclear weapons that is performed underground. When the device being tested is buried at sufficient depth, the nuclear explosion may be contained, with no release of radioactive materials 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.
context_section_description: 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 US Joint Chiefs of Staff thus obtained the agreement of the United States Atomic Energy Commission (AEC) to perform experiments on both surface and sub-surface detonations. The Alaskan 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 fission weapon that was then being considered for use as a cratering and bunker-buster weapon. The explosion resulted in a cloud that rose to 3,500 m (11,500 ft), and deposited fallout to the north and north-northeast. The resulting crater was 79 m (260 ft) wide and 16 m (53 ft) deep.
  The next underground test was Teapot Ess, on 23 March 1955. The one-kiloton explosion was an operational test of an 'Atomic Demolition Munition' (ADM). It was detonated 20.4 m (67 ft) 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 91 m (300 ft) wide and 39 m (128 ft) deep. The resulting mushroom cloud rose to a height of 3,700 m (12,000 ft) and subsequent radioactive fallout drifted in an easterly direction, travelling as far as 225 km (140 mi) from ground zero.
  On 26 July 1957, Plumbbob Pascal-A was detonated at the bottom of a 148 m (486 ft) 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 facility on Amchitka, was detonated on 6 November 1971.  At approximately 5 megatons, it was the largest underground test in US history.
caption: Buster-Jangle Uncle, the first underground nuclear explosion
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