Isegoria

Back in the “Atoms for Peace” era, the US’s Project Plowshare attempted to harness peaceful nuclear explosions for massive public works. The first test, Project Gnome, took place roughly 40 km (25 mi) southeast of Carlsbad, New Mexico, in an area of salt and potash mines along with oil and gas wells:

It was learned during the 1957 Plumbbob-Rainier tests that an underground nuclear detonation created large quantities of heat as well as radioisotopes, but most would quickly become trapped in the molten rock and become unusable as the rock resolidifed. For this reason, it was decided that Gnome would be detonated in bedded rock salt. The plan was to then pipe water through the molten salt and use the generated steam to produce electricity. The hardened salt could be subsequently dissolved in water in order to extract the radioisotopes. Gnome was considered extremely important to the future of nuclear science because it could show that nuclear weapons might be used in peaceful applications. The Atomic Energy Commission invited representatives from various nations, the U.N., the media, interested scientists and some Carlsbad residents.

“We’re going to set off an atomic bomb in a cave. You wanna come?”

Gnome was placed 361 m (1,184 ft) underground at the end of a 340 m (1,115 ft) tunnel that was supposed to be self-sealing upon detonation. Gnome was detonated on 10 December 1961, with a yield of 3.1 kilotons. Even though the Gnome shot was supposed to seal itself, the plan did not quite work. Two to three minutes after detonation, smoke and steam began to rise from the shaft. Consequently, some radiation was released and detected off site, but it quickly decayed.

The cavity volume was calculated to be 28,000 ± 2,800 cubic meters with an average radius of 17.4 m in the lower portion measured. The Gnome detonation created a cavity about 170 ft (52 m) wide and almost 90 ft (27 m) high with a floor of melted rock and salt. A new shaft was drilled near the original and, on 17 May 1962, crews entered the Gnome Cavity. Even though almost six months had passed since the detonation, the temperature inside the cavity was still around 140 °F (60 °C). Inside, they found stalactites made of melted salt, as well as the walls of the cavity covered in salt. The intense radiation of the detonation colored the salt multiple shades of blue, green, and violet. Nonetheless, the explorers encountered only 5 milliroentgen, and it was considered safe for them to enter the cavern and cross its central rubble pile. While the three-kiloton explosion had melted 2400 tons of salt, the explosion had caused the collapse of the sides and top of the chamber, adding 28,000 tons of rubble that mixed with the molten salt and rapidly reduced its temperature. This was the reason the drilling program had originally been unsuccessful, finding temperatures of only 200 F, without high pressure steam, though the boreholes had encountered occasional pockets of molten salt at up to 1450 F deeper amid the rubble.

Today, all that exists on the surface to show what occurred below is a small concrete monument with two weathered and slightly vandalized plaques.

Other proposals under Project Plowshare included widening the Panama Canal, constructing a new sea-level waterway through Nicaragua nicknamed the Pan-Atomic Canal, cutting paths through mountainous areas for highways, and connecting inland river systems.

No mention of draining the Mediterranean though.

(Hat tip to commenter Sam J.)

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