1962: Nevada detonated a nuke aboveground—what appeared?

The Experiment That Moved a Mountain

On July 6, 1962, at 10:00 a.m. Pacific time, the Atomic Energy Commission detonated a 104-kiloton thermonuclear device buried 635 feet beneath the desert floor of the Nevada Test Site's Yucca Flat. The blast was part of Operation Storax, a series of 47 nuclear tests conducted that year, but Sedan stood apart: it was explicitly designed not to test a weapon but to move dirt. The detonation vaporized rock, superheated groundwater into steam, and sent a dome of earth rising 300 feet into the air before it collapsed into a crater 320 feet deep and 1,280 feet wide. In 6.5 seconds, Sedan displaced 12 million tons of soil and created the largest man-made crater in the United States. The mushroom cloud rose 12,000 feet, and radioactive fallout drifted across every state in the continental U.S. More residents were exposed to radiation from Sedan than from any other test in the continental United States.

Plowshare: Atomic Earthmoving as Utopia

Sedan was the signature demonstration of Project Plowshare, the Atomic Energy Commission's 1958–1977 program to find peaceful uses for nuclear explosives. Scientists envisioned using bombs to excavate harbors, canals, highway cuts, and even a second Panama Canal across Nicaragua or Colombia. Edward Teller, the physicist known as the father of the hydrogen bomb, championed the idea, arguing that a single nuclear charge could do the work of years of conventional digging at a fraction of the cost. Sedan proved the concept worked: the crater's volume exceeded 7 million cubic yards, and engineers calculated that nuclear excavation could cost as little as 15 cents per cubic yard compared to several dollars for dynamite and bulldozers. Plans were drawn for Operation Chariot, which would use five hydrogen bombs to carve an artificial harbor at Cape Thompson, Alaska, and for a 160-bomb canal across the Negev Desert in Israel.

The Fallout Nobody Wanted to Count

But Sedan also produced consequences nobody could excavate away. The blast released 880,000 curies of iodine-131 into the atmosphere—7 percent of the total fallout from all U.S. atmospheric tests combined. Monitors detected elevated radiation levels in Iowa, Illinois, Nebraska, South Dakota, and Utah within 24 hours. Milk samples across the Midwest showed contamination. The Atomic Energy Commission had predicted the fallout would stay local; instead, the test violated the Limited Nuclear Test Ban Treaty before it was even signed. Sedan was the last cratering test the U.S. conducted in the continental United States, and by 1963 public opposition had grown fierce. Downwinders—residents living near the test site—later won compensation lawsuits. The dream of atomic excavation died not because the technology failed but because nobody wanted the fallout in their backyard.

A Crater You Can Visit

Today, the Sedan crater remains the most visible scar of the atomic age in North America. In 1994, it was listed on the National Register of Historic Places as a monument to Cold War science. The Nevada National Security Site offers monthly public tours to the rim, where visitors peer into a bowl large enough to hold a 20-story building. The crater floor has become a desert wetland, catching rainwater and supporting stands of rabbitbrush and saltbush. Radiation levels at the rim measure around 6 microroentgens per hour—slightly elevated but safe for short visits. The site stands as both an engineering marvel and a cautionary tale: proof that humans could reshape the earth itself, and a reminder that some questions—like whether we should—matter more than whether we can.