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Salt Locker

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Salt-Dome

Salt Locker

 Josh Jack

 

Below Baton Rouge, Louisiana lacks much topographical relief. Slender strands of high ground gird the banks of rivers, lakes and bayous (extinct and contemporary) where these waterways have built up natural levees in times of flood. Higher manmade levies might rear several stories high along the Mississippi and Atchafalaya, and tailing ponds along the River Road tower many stories over the surrounding landscape: colossal dikes holding in toxic, alkaline slurries of arsenic, uranium, radon, caustic soda, chromium, methyl-mercury, and other various metallic compounds and industrial waste. Among the backswamps and bays at the waterway’s flanks one might spot the occasional chenier (from French, meaning ‘place of oaks’) which have been braided by centuries of bioaccumulation into hammocks of slightly higher land, floating just above the swamps and marshes, where lowland oaks and other bottomland hardwoods hold court. The Mississippi River itself registers only about two inches per mile of fall over the last two-hundred miles of its course; its bed runs up to two-hundred feet below sea level through this stretch, its waters pushed gulfward by sheer momentum and the enormous pressure of its upstream waters. And yet, here and there, strange hillocks rise above the swamp, looming as high as seventy feet above their surrounds. How could this be?

Well, aeons ago what is now Louisiana looked quite different. Water flowed into a restricted marine basin (one finds contemporary examples of these endorheic basins in Death Valley, The Great Salt Lake, and the various salt flats and dry lakebeds of the Great Basin.) With no outlet to the sea vast quantities of salt accumulated, and, as water evaporated, this salt was deposited in thick layers on the bed of the intermittently dry sea(s). Over time the basin changed and found its oceanic outlet. New, less saline, alluvial deposits began to accumulate on top. These layers began to compress into denser and denser sheets as more and more sediment accumulated and the pressure exerted downward increased. Salt, however, possesses a crystalline structure like ice that is quite resistant to compression (though it is actually quite ductile, allowing it to flow along seams and fault lines.) Consequently, these salt deposits began to actually float upward along faults in the denser rock in a process that has taken roughly 100 million years. As the salt columns rise they deform the land above, mushrooming against stronger rock layers, and breaking through weaker ones, occasionally erupting onto the surface (though rare, these eruptions can even form salt glaciers!)

Today, these salt domes comprise some of the state’s most famous islands. The largest are aligned like beads on a taught string southeast of New Iberia: Jefferson Island, Avery Island (of Tabasco Hot Sauce fame,) Weeks Island, Cote Blanche Island, and Belle Island. Nearly 150 other salt domes pepper our wetlands (with many more bulging from the sea floor off the coast.) Those with any prominence are usually crowned with human settlement; others are mined, either for their sodium-chloride, or for the oil and natural gas that they channel upwards and entrap. Occasionally, the proximity of such developments can have startling repercussions.

On the morning of November 21st, 1980 an oil derrick leased to Texaco was in the process of drilling an exploratory well in Lake Peigneur, a small, freshwater lake just north of Vermillion Bay, (and just southwest of the salt dome that makes up Jefferson Island) when, at a depth of 1,230 feet, the drill seized up and the derrick began to list. It turns out they had punctured the vast excavations of the Diamond Crystal Salt Mine. Salt, incidentally, is highly soluble in water and as the lake to poured through the borehole into the mine the bed of the lake began to melt away into an ever widening gyre. A giant whirlpool formed on the surface, swallowing the oil platform whole (all fifteen stories of it.) It then engulfed another nearby oilrig and began to gorge itself on boats: small fishing dinghies, pile drivers, shrimp boats and barges. Below the surface the waters began to gnaw at the support columns of the mine, and within the hour nearby land began to slump into the torrent, bearing trees, houses and docks along into the throat of the maelstrom. Within four hours the entire volume of Lake Peigneur had been sucked down into the belly of the salt dome, but a shallow outlet to the south still connected the body of water to Vermillion Bay; as the sun tacked westward this outlet reversed its course and gulf waters began to charge inland towards the waiting maw. The mine was not yet sated.

Miraculously, no one was killed. The fifty-five workers who were in the mine when the ceiling was breached managed to evacuate before they could be trapped and drowned, and the platform workers likewise abandoned their vessel before it was seized and cast down into the sunless sea. A handful of fisherman were on the water at the time of the accident, and though their various escapes were certainly harrowing, none perished. Their boats were not so lucky. Nor were the various homes built upon the roughly sixty-five acres of land that were swallowed over the course of the next two days. During that time residents witnessed something amazing: a 150 foot high waterfall — the largest to have ever existed in the state — rushing down into the bowels of the earth. On the third day the torrent began to slack, and, as the waters returned to the level of the sea, boats began to pop to the surface like corks. As pressure differentials deep below began to equalize, colossal geysers erupted in New Iberia, spraying muddy water as high as four-hundred feet. Lake Peigneur was never the same: what was once a shallow, freshwater lake was now a very deep, saltwater lake. Nearly overnight the formerly eleven foot deep body of water became the deepest lake in the Southeast, and among the deepest in all of North America, at more than 13,000 feet. Where formerly brim and bass had darted among the weeds, large gulf fishes now moved in to take their place.

If the Lake Peigneur Disaster taught the oil and gas industry caution, it also taught them something else: the enormous capacity of these subterranean columns of salt. When water is injected into the heart of these miles deep salt domes, and the brine extracted, a huge void is left behind. Today many of Louisiana’s salt domes find use as vast underground silos for natural gas, ethylene and oil. (The largest, roughly one-hundred miles due south of New Orleans, holds 727-million barrels of oil as a part of the United States Strategic Petroleum Reserve.) Beneath Assumption Parish, near Bayou Corne and just northwest of Thibodaux, lies the Napoleanville Dome, a former salt mine that had since found use as a series of storage caverns for oil, gas and brine. In 2010 Texas Brine began to expand one of its storage caverns, even though the chamber was already within a hundred feet — a geological hair’s-breadth — of the nearest oil and gas caverns, and preliminary pressure tests proved unsatisfactory. In 2012 local residents began to notice unusual tremors and bubbling jets of methane. The smell of oil lingered on the air. Fearing a ruptured pipeline, scientists were called in to diagnose the problem; what they found was much worse. The outer wall of the salt dome had collapsed, allowing sediment and ground water to rush in and oil and gas to seep out. While the Governor ordered a mandatory evacuation of the area, the nearby land began to sink into the earth. As with Lake Peigneur, the breach, more than a mile below the surface, quickly widened, and subsidence increased at a geometrical pace, though the process now played out over the course of years rather than days. Although the Bayou Corne Sinkhole has now mostly stabilized, it ultimately swallowed some 36 acres, displacing nearly 300 residents and gobbling up homes, trees and great chunks of land. The evacuation order was rescinded in 2016, but the hole continues to widen at a rate of about two feet per year. No one can say for sure how much oil and methane escaped in the process, nor how much might yet be slowly seeping to the surface…

The story of Louisiana is as much a product of what lies hidden beneath our feet as of the visible forces that sculpt the surface. Certain things, long buried, have a way of turning up with a shock, whether they be Jurassic salt deposits, or Carboniferous petroleum — repressed traumas, or the consequences of past sins. And yet the buried and invisible seem smaller, even manageable, because we cannot see or touch the edges of the processes at work. Past success and extravagant profits have taught the engineers and business interests the easy conviction of hubris even as history belies this confidence with periodic  demonstrations of how quickly one miscalculation, then another, can compound into a disaster many orders of magnitude beyond our ability to control. The wages of ignorance is catastrophe; if the powers that be fail to recognize this fact, it’s only a matter of time before the next community is swallowed up like Kubla Khan and all must close their eyes again in holy dread.