Lake Peigneur is located in Louisiana, 125 to 150 miles west of New Orleans. If you’d visited it thirty-five years ago or so, you would have found a freshwater lake that, at its deepest, was only about ten feet, well stocked with lots of fish appropriate for the environment. And if you were there on November 20, 1980, you would have seen a 150-foot-high oil derrick disappear into a lake barely deep enough to sink a sailboat.

Texaco, an American petroleum company (since acquired by Chevron), was drilling in Lake Peigneur, hoping to find oil roughly 1,400 feet (430 meters) below the water’s surface. We’re not entirely sure what happened that day—when 150-foot structures disappear into ten feet of water, there will always be more questions than answers—but more likely than not, the Texaco engineers made a small mistake. Their 14-inch (.35 meter) drill bit was off the mark and went a bit sideways. Normally, that would not be a big deal—it would just mean that the rig was not going to find any oil. But Lake Peigneur wasn’t sitting on an oil reserve—or, at least, not only on an oil reserve. About 1,400 feet below the surface of Lake Peigneur was the third level of a salt mine operated by the Diamond Crystal Salt Company. And the hole the oil rig created let the lake’s water right into the mine’s ceiling.

If you’ve ever added salt to water, you know that the two mix very well—the salt dissolves, and pretty quickly. And if you’re operating a large-scale salt mine, it is a very, very bad thing to have an entire lake— 2.5 billion gallons of water, in this case—start flowing in through a crack in a ceiling. This is especially true in the above case, because the salt mine in question (and pragmatically, this makes sense for most salt mines) used salt pillars to support the ceilings against the weight of the levels above. When the water comes rushing in, everything collapses. Everything—including 150-foot oil rigs.

Within minutes, a whirlpool formed at the surface of Lake Peigneur as the water drained into the mine. The whirlpool began sucking everything in the lake into its ever-increasing vortex. Down went the drilling rig and its platform; a dozen boats, many of which were barges carrying things such as trucks; and, perhaps most incredibly, sixty-five acres of land, including an entire island. Delcambre Canal, which before that day was the lake’s outlet (ultimately) to the Gulf of Mexico, reversed course, bringing saltwater from the Gulf into the lake. For a few days, the reversed water flow created a 150-foot waterfall—easily the tallest in Louisiana at the time. When the bottom finally finished falling out of Lake Peigneur, the sixty- year-old salt mine was gone, and the once-shallow freshwater lake was now a saltwater basin with a maximum depth of 200 feet.

Amazingly, the death toll from the Lake Peigneur disaster was zero. The fifty-five salt mine workers and all the people on the rig and in boats managed to evacuate in time.

Bonus fact : Salt and oil have a long history. Edwin Drake, credited with being the first American to successfully drill for oil (at the time to be used for lamps, as whale oil had become expensive), set up the historic rig in Titusville, Pennsylvania in 1858. Since Drake’s drill was the first of its kind, he had to invent a way to explore what lay beneath. He decided to simply copy the well-established methods of drilling for salt. He also added a cast-iron pipe to allow him to drill through bedrock without water seeping into the drilling area, and with this innovation, the salt drilling method became the standard for early oil rigs.

Take the Quiz : Name the top 20 salt producing countries.

From the Archives: Temple of Rock Salt: A Polish church made of salt. Also, this.

Related: A LEGO oil rig.