Lake Peigneur and adjacent Jefferson Island sit on an ancient salt dome formed from salt deposited more than 165 million years ago during the mid-Jurassic period, then buried by Mississippi River sediment whose weight pushed the salt upward to create one of Louisiana’s Five Islands. Jefferson Island rises about 50 feet above the surrounding landscape, and salt mining there throughout the 1900s created a vast cavern beneath the lake. On Nov. 20, 1980, an oil drilling company conducting exploratory drilling accidentally pierced the lake bottom, opening a path for Lake Peigneur to drain into the salt mine below. Within hours, a huge whirlpool pulled in a drilling rig, several barges, boats, a newly constructed house, and 65 acres of land, including a botanical preserve. The suction became so powerful that the Delcalmbre Canal reversed direction and formed a temporary 150-foot waterfall, and after two days canal water refilled the nearly empty lakebed. Once pressure equalized, nine lost barges rose back from the bottom. No lives were lost in the mine, but the disaster caused years of damage and transformed what had been a 10-foot-deep freshwater fishing hole into deep, brackish water, while a lone chimney still stands above the surface as a reminder of the event.