Underground nuclear test

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 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.

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; this was traced to packaging materials sourced from Indiana crops, contaminated by the Trinity and later tests at the Nevada Test Site, over 1,000 miles away. 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 the Rongerik and Rongelap atolls, and a Japanese fishing boat known as the Daigo Fukuryū Maru (Lucky Dragon). Prior to this test, there was "insufficient" appreciation of the dangers of fallout.

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