The device is detonated remotely from a surface control bunker. Nuclear explosion vaporizes underground rock, creating an underground chamber filled with superheated radioactive gas. As it cools, a pool of molten rock builds up at the bottom of the chamber. Underground nuclear tests are the detonation tests of nuclear weapons that are carried out underground.
When the device being tested is buried deep enough, the nuclear explosion can be contained, without releasing radioactive materials into the atmosphere. The objective of the test-ban treaty was to limit atmospheric precipitation and exposure to radioactive materials. When a weapon is buried deep enough, its explosion can be contained in the ground; the depth depends on the size of the bomb. If the bomb is not buried deep enough in the ground, it will not necessarily produce a classic mushroom cloud, but rather a giant cloud of dust and dirt will explode in the sky, as seen above.
Detonation of nuclear weapons above the earth sends radioactive materials up to 50 miles into the atmosphere. Large particles fall to the ground near the explosion site, but lighter particles and gases move to the upper atmosphere. Particles that are dragged into the atmosphere and fall back to Earth are called rain. Rain can circulate around the world for years until it gradually falls to Earth or is brought back to the surface by precipitation.
The trajectory of rain depends on wind and weather patterns. The Comprehensive Nuclear-Test-Ban Treaty bans nuclear testing anywhere on the planet's surface, atmosphere, underwater and underground. The first Operation Crossroads underwater nuclear test was conducted by the United States in 1946 at its Pacific Proving Grounds in the Marshall Islands for the purpose of evaluating the effects of nuclear weapons used against naval vessels. From then until the signing of the Comprehensive Nuclear-Test-Ban Treaty in 1996, most nuclear tests were conducted underground, in order to prevent nuclear fallout from entering the atmosphere.
Some studies and evaluations, including an evaluation by Arjun Makhijani of the health effects of nuclear weapons complexes, estimate that cancer deaths due to global radiation doses from nuclear test programs in the atmosphere of the five nuclear-weapon States amount to hundreds of thousands. See a rough overview of all nuclear tests conducted to date, as well as the status of the CTBT of countries that have conducted nuclear tests. France closed and dismantled all of its nuclear test centers in the 1990s, the only nuclear-weapon State to date. These monitors were originally designed to detect radionuclides that were released after the detonation of a nuclear weapon.
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) The CTBT is a legally binding global ban on the testing of nuclear explosives. At first, neither the United States nor the Soviet Union had many nuclear weapons to spare, so their nuclear tests were relatively limited. Less than ten years later, with the anticipated transition to a majority-elected government, South Africa dismantled all its nuclear weapons, the only nation to date that voluntarily renounced nuclear weapons under its full control. If data from IMS stations indicate that a nuclear test has been carried out, a Member State may request that an on-site inspection be carried out to collect evidence to make the final assessment of whether a nuclear explosion actually occurred in violation of the Treaty.
Later, in 1955, United States Operation Wigwam conducted a single submarine nuclear test at a depth of 600 m to determine the vulnerability of submarines to nuclear explosions. Underground nuclear testing was banned by the 1996 Comprehensive Nuclear-Test-Ban Treaty (CTBT), which bans all nuclear explosions on Earth. Both India and Pakistan immediately moved to announce unilateral moratoriums on nuclear testing and have not conducted nuclear tests since 1998.