October 1964 Nuclear testing in Mississippi http://mashable.com/2016/11/06/mississippi-nuclear-test/#QAtiwfQCDiqT [many photographs] Waiting on the big bang
by Alex Q. Arbuckle, 6 Nov 16 At 10 a.m. on Oct. 22, 1964, a five-kiloton nuclear device was detonated in Lamar County, Mississippi.
The previous year, as a response to rising public anxiety over the potential fallout of bigger and bigger test explosions, the United States, Great Britain and the Soviet Union had signed the Partial Test Ban Treaty, which prohibited all nuclear testing in the atmosphere, underwater and in outer space. Underground detonations were not banned in the treaty because it was still technically unclear how they could be detected to ensure compliance.
After signing the treaty, the United States government created Project Dribble, an effort to study how underground nuclear tests could be detected — or hidden.
The site of Project Dribble’s first detonation was 28 miles southwest of Hattiesburg in the Tatum Salt Dome, a massive Mesozoic salt deposit 1,000 feet below the ground.
The plan called for two detonations. The first, code-named Project Salmon, would be an explosion 2,700 feet down in solid salt. The second detonation, Project Sterling, would use a smaller bomb in the cavity left behind by the first blast.
Scientists hypothesized that the shockwaves of the second detonation would be muffled by the cavity, effectively concealing it from seismographic detection. The first blast was scheduled for Sept. 22, but was postponed repeatedly because the wind direction was not ideal.
Finally, on Oct. 22, the conditions were right.
Four-hundred residents were evacuated from the area around and downwind of the blast site. For their trouble, adults were paid $10 and children $5.
At 10 a.m., the Project Salmon device detonated with approximately one-third of the power of the bomb that destroyed Hiroshima.
The earth rose and roiled in waves, pecans fell from trees, dogs howled in fear, creeks ran black with disturbed sediment, and buildings thirty miles away swayed for minutes on end.
Within a week, hundreds of residents had filed damage claims with the government, citing burst pipes, cracked masonry and suddenly dry wells. The test was a success, however. The blast vaporized a spherical void in the salt 110 feet in diameter. When sensors were lowered into the cavity more than three months later, temperatures still measured over 400 degrees Fahrenheit.
Two years after Project Salmon, the second part of the test, Project Sterling, was carried out. A much smaller bomb — equal to 350 tons of TNT versus the first bomb’s 5,000 tons — was detonated in the cavity.
As the scientists hypothesized, the cavity absorbed nearly all of the blast’s seismic force. People on the surface barely felt a bump.
The blasts, which gave the government plenty of data on how underground nuclear tests could be hidden and detected, were declared a success — the only nuclear detonations to ever occur in the eastern United States.
