Jefferson Island is a salt dome located in Iberia Parish, in Southern Louisiana. The term “Island” is a bit of a misnomer, as Jefferson Island and its nearby neighbor Avery Island are not actually islands at all, but rather protruding salt domes which stand out from the surrounding landscape. These salt domes were formed through the slow evaporation of the ocean which once covered the area, and they are a substantial natural resource.
This island is part of a group of similar structures known collectively as the Five Islands. In addition to Avery Island, the Five Islands also include Weeks, Belle Isle, and Cote Blanche. Each of the islands sits on top of a dome of salt, and in addition to salt, the Five Islands also have rich oil and gas deposits which have been heavily exploited over the years. Because of the salt deposits present on the Five Islands, they became a fiercely defended property during the Civil War, when salt was at a premium. Avery Island, owned by the Tabasco Company, was once also used to produce cayenne peppers.
Originally, Jefferson Island was known as Orange Island. It was purchased by actor Joseph Jefferson in 1869 for the purpose of establishing a summer home, and it was ultimately named after him. Jefferson built a mansion on the site which is now on the National Register of Historic Places; the mansion today is surrounded by sprawling gardens established by John Lyle Bayless, who purchased the Island after Jefferson's death.
The Diamond Salt Company mined for salt on the Island until 1986, while Texaco drilled for natural oil and gas resources. Today, the underground salt dome is used to store natural gas, because it is a very stable environment for long-term storage. Some suggestions have been made that the salt domes on the Five Islands would also make a good storage facility for nuclear material, although concerns about the risk of seepage make it unlikely that these suggestions will ever be put into action.
In 1980, Jefferson Island attracted national attention when Texaco made an unfortunate mistake while drilling for oil, causing neighboring Lake Peigneur to collapse into the salt mine on Jefferson Island. The lake formed a whirlpool which sucked a wide variety of items into the mine, and the area was flooded with water from the Delcambre Canal, which normally flowed in the opposite direction. As the salt mine filled with water, it forced air out, forming impressive geysers which towered over the area for several days until the water pressure was equalized.