September 13, 1963: US performs underground nuclear test at Nevada Test Site.
One hundred above-ground nuclear tests were conducted at the Nevada Test Site (NTS) between January 27, 1951, and July 17, 1962. On August 5, 1963, the Soviet Union and the United States signed the Limited Test Ban Treaty (LTBT), which prohibited nuclear tests in the atmosphere, under water, and in space. From that time, until the end of testing in 1992, nuclear tests at the NTS were conducted underground.
After the nuclear detonation in a shaft, a formation called a “subsidence crater” usually occurred. Such craters are not caused directly by the nuclear blast itself, but from the earth’s surface sinking due to the void created by the underground explosion’s liquefying of surrounding rock. Some subsidence craters formed shortly after the detonation, others took much longer to develop. Visitors can view subsidence craters in the Yucca Flat areas of the NTS during public tours. Some tours include driving into the large crater created by the 249-kiloton Bilby test, detonated September 13, 1963.
Bilby’s crater is 1800 feet wide, and 80 feet deep. The device which created Bilby was set off 2400 feet underground.