AEC detonates 'Sedan' 636 feet underground at Yucca Flat; 12 million tons of earth go skyward
By 1962, the Atomic Energy Commission wanted Americans to see the bomb as a tool, not just a weapon. On July 6, at Yucca Flat in the Nevada National Security Site, engineers lowered a thermonuclear device 636 feet into the desert alluvium and detonated it as part of Project Plowshare. The blast, code-named Sedan, threw more than 12 million tons of earth into the sky and left a crater about 330 feet deep and nearly a quarter-mile across. The radioactive cloud didn't stay in Nevada. It drifted east, dropping fallout across the Midwest and exposing more than 13 million Americans to radiation, more than any other nuclear test in U.S. history.
Sedan became the test that ended the idea of nuclear excavation in America. The fallout it dropped on Iowa, Nebraska, South Dakota, and Illinois turned "peaceful atom" optimism into public alarm, and no U.S. excavation test of its kind has been attempted since. The crater it left behind now sits on the National Register of Historic Places, a monument to a program the country decided not to finish.
QHow did the Sedan test help solve a mystery about a crater in Arizona?
Sedan's unusually large, atmosphere-venting blast gave geologists something they had never had before: a fresh, observable crater created by a massive explosion under conditions they could study directly. Comparing its structure to Arizona's Barringer Crater helped scientists confirm that Barringer had been carved by a meteor impact rather than volcanic activity, a debate that had lingered for decades. A test built to move earth for engineering purposes ended up settling a question in planetary science instead.
QWhat is actually growing in the Sedan crater today?
Not much, and what does grow is telling. A 1993 survey found that the native perennial shrubs that once covered the site had shown no recovery decades after the blast. The dominant plant now is Salsola tragus, better known as Russian thistle or tumbleweed, an invasive species that colonizes disturbed ground more aggressively than anything native. The crater has become, in effect, a long-running experiment in ecological succession nobody planned to run.
QWhy do thousands of people visit a nuclear test crater every year?
The Department of Energy's Nevada Site Office runs free monthly public tours of the Sedan crater, and more than 10,000 people show up annually to see it. Visitors stand at the rim of a hole 330 feet deep and nearly a quarter-mile across, the largest crater ever made by human hands in the United States. It is one of the few Cold War test sites turned into a standing tourist attraction rather than a sealed-off ruin.
