Submitted by Charlton Stanley (aka Otteray Scribe), Guest Blogger
There are gigantic salt deposits under the state of Louisiana. Geologists tell us the salt dome under Assumption Parish is about the same size as Mt. Everest. Some of the deposits are as deep as 35,000 feet as shown in this not-to-scale drawing. In fact, huge salt deposits are under large patches of the North American continent along the Mississippi River valley all the way up to Lake Erie. The city of Cleveland is sitting on top of a large salt deposit.
Salt settled out of the water when these areas were part of the ocean as the continent of North America was forming. We have all seen what happens if you dissolve salt in water. It reaches a saturation point, where no more salt can be dissolved. At that point, the excess salt settles to the bottom. That process is still going on at the surface in places like the Great Salt Lake and the Dead Sea. Once the water evaporates, it leaves behind places like the famed Bonneville Salt Flats. The excess salt in the water in those formative years of this continent settled out into enormous deposits. The primary deposits of salt are deep underground, as far as ten thousand feet or more. However, like glacier ice, solid crystal salt becomes somewhat plastic under great pressure. At ten thousand feet, the overburden of rock and sediment creates pressures of thousands of pounds per square inch. Salt deposits find weak places in the rock, and start squeezing upward in plumes, called “salt domes.” These extrusions come nearer the surface, making the salt more accessible so it can be mined. When I lived in Louisiana as a kid, I remember the salt mines being an everyday topic of conversation. The salt is not only used for food, but has many industrial uses as well. During World War Two, the salt mines provided essential minerals used in the manufacture of ammunition and high explosives. Salt mining in Louisiana has been going on since before the Civil War. Some of the mine shafts go down as much as ten thousand feet, and some of the salt caverns that have been mined are enormous.
Some of those salt dome mine caverns have been used for storing things, such as butane and natural gas under pressure. Let’s see now. We have a salt dome near the sea holding about one and a half million gallons of liquified gas under pressure at 1,000 pounds per square inch. What could possibly go wrong? Add to that an abundance of oil deposits. Drilling for oil and gas is big business along the Louisiana Gulf Coast. Drills have a bad habit of punching holes in things. The Lake Peigneur Disaster of November 20, 1980 was the result of a simple miscalculation on the part of engineers responsible for telling the drill crew where to drill.
When the salt is not fractured, it retains its integrity as a vault. However, geological and human activity can cause fracturing. Additionally, mining creates a cavity, and the sidewalls must be thick and strong enough to resist side pressure from underground oil, gas and rocks. Like a crack in the foundation of a house, water can get into cracks. Water pressure at 5,000 feet is 2,165 pounds per square inch. At 10,000 feet, water pressure is 4,350 pounds per square inch. It does not take much of a crack for water to get in. At those pressures, a leak the size of a straight pin has the penetrating power of a cannon shell.
Assumption Parish is south of Baton Rouge, the state capitol. A parish is the Louisiana equivalent of a county. Parish governments are supervised by a Police Jury, a body of elected citizens somewhat similar to County Commissions in other states. The Parish has a web site, a blog and a YouTube channel. Over a year ago, bubbles were observed coming from the general area of the salt dome. At first the bubbles were a mystery. Then crude oil began appearing. At that point, geologists realized the integrity of the salt dome sidewall had been breached. A sinkhole began to appear in Bayou Corne in Assumption Parish. It has grown steadily since last year, and by this past week, was about 26 acres in size. The sinkhole is due to the collapse of a salt dome like the illustration at the top of this story. Some experts on the scene make a difference between a sinkhole and a salt dome collapse, saying the latter is a far worse environmental and geological disaster than a sinkhole. Because a true sinkhole is due to erosion of rock and sand, it can only get a few hundred feet deep at most. On the other hand, a salt dome collapse has the potential to end up more than two miles deep. No matter what it is called, the hole is getting larger by the day, and after the most recent sloughing this week, workers were pulled back from the berms and service roads surrounding the sinkhole. The increased rate of sloughing off edges of the hole was making it too dangerous to stay there.
An incident last week illustrated how the edges of the sinkhole are eroding away. Watch this short video made by work crews as the underwater edge of the sinkhole creeps toward a stand of 100 foot tall Cypress trees. The floating booms seen in the video were for containing the crude oil floating on the pond. Seeing these giant trees sink is not the most disturbing thing about this sinkhole. Despite the fact it is about twenty five miles from the nearest open water, the sinkhole has been exhibiting tidal wave action. That means it is probably somehow connected to the Gulf of Mexico deep underground, either through old mine shafts or cracks. Water pumping back and forth will cause more scouring than stagnant water. An unlimited water supply also means more salt can dissolve because the water will not become over-saturated with salt.
No one knows for sure when the sinkhole will stop growing. Depending on who you talk to, some geologists are pessimistic about these new developments, and want to post evacuation warnings as far as 25 to 100 miles from the sinkhole. There is another concern as well. No one knows exactly how all this geo/hydraulic activity in south Louisiana will affect the maze of fault lines along the Mississippi River valley up into the Great Lakes. The most famous of these fault systems is the New Madrid Seismic Zone. If it proves to be true the side walls of the dome were breached, the situation becomes unsalvagable. Maps show that a substantial portion of Louisiana could end up underwater unless the hole stops growing.The video below shows that unusual wave action.
A few days ago, Governor Bobby Jindal, with Attorney General Buddy Caldwell beside him, held a press conference in which he said the state is going to sue the salt mining company, Texas Brine. He didn’t say anything about suing any of the oil companies, such as BP.
The floor is open for discussion.
Gene,
No problem.
OS,
Nice article. And you’re right, the issue in Bayou Corne is very different from limestone (karst) sinkholes. It could be devastating.
Elaine, the big difference between what is happening in LA that is different from both Kansas and FL, is this sinkhole has the potential to go down anywhere from two to five miles deep. That could put enormous shearing pressure on fault lines further up the river. Also, water acts as a lubricant when forced into faults. That is a Bad Thing. For potential harm, you don’t need to look further than Port Gibson, Mississippi. The Grand Gulf nuclear plant owned by Entergy Corp. is there.
Yes, I referenced that in a link near the top of the story.
Otteray,
Do you recall the recent story about a Florida resort collapsing into a sinkhole?
Condos collapse into sinkhole near Disney World
http://www.usatoday.com/story/news/nation/2013/08/12/sinkhole-causes-resort-villa-to-partially-collapse/2641949/
*****
Sinkholes: common, costly and sometimes deadly
By Michael Pearson, CNN
http://www.cnn.com/2013/03/01/us/florida-sinkhole-explainer
Excerpt:
(CNN) — The kind of sinkhole that suddenly opened up under a Florida home is more common than you might think. Let’s take a look at what causes them, where they happen and just how dangerous and costly they can be:
What causes sinkholes?
Many sinkholes form when acidic rainwater dissolves limestone or similar rock beneath the soil, leaving a large void that collapses when it’s no longer able to support the weight of what’s above, whether that be an open field, a road or a house. These are called “cover-collapse sinkholes,” and it would appear this is what’s happening in Florida, where the ground beneath the home suddenly gave way.
Where do they happen?
Sinkholes are particularly common in Florida, which rests on a nearly unbroken bed of limestone, according to the Florida Sinkhole Research Institute. Central Florida, including the Tampa area, is particularly known for sinkholes. In fact, Hillsborough County, where Thursday’s collapse occurred, is known as part of Florida’s so-called Sinkhole Alley, where two-thirds of insurance claims for sinkhole damage occur, according to a report prepared for state lawmakers in 2010. Other places that frequently see sinkholes include Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania, the U.S. Geological Survey says.
gbk,
yes, that maze of faults are strike shift type. I was in St. Louis on November 9, 1968 when the Cottage Grove Fault let go. That was 5.4 on the Richter Scale. No fatalities, but several buildings were badly damaged. Previous to that incident, the Cottage Grove Fault was unknown. That is a very fragile fault system, and there is a 90% chance of a Richer 6-7 quake before 2055.
Great Article OS!
When I read your article, it made me think of this sinkhole incident:
http://www.cnn.com/2013/03/01/us/florida-sinkhole
Jokes aside, this is very serious. The last consequential New Madrid quake, that of 1811-12, changed the course of the Mississippi River. This has the potential to surpass the recent quake off of Sendai, Japan, or the massive quake west of Aceh, Indonesia, that also changed the orbit of the earth. In layman’s terms, we are talking about a 9+ seismic event, certainly no reason for humor. What are the people of this huge region going to do to prepare for what appears to be practically a geographic changing event. Intense shock waves could easily be felt over a 1,000,000 square mile area. Scientists from University of Missouri and Northwestern University, whose work had showed the phenomenon that altered the Mississippi, was an event similar to a crow’s foot crack, and that New Madrid was the a ‘dead end fissure’, connected, but, not a critical link to any significant faults. Thus, they had only recently ruled out a repeat of anything remotely comparable to the 1811-12 quake. Their work was scientifically sound. In this case, uninhibited drilling and “fracking” are the likely culprits. In other words, the cause once again, that never to be ruled out human instigator of ecological disaster greed. Armed with this new data, they will need rush back to the labs, and enter this new information into their ‘through and back ‘matrices, so that they can more actually calculate the area now under serious threat. At this point, establishing a timeline will be extremely difficult. Talk of lawsuits is almost ridiculous. Injunctions are needed aside,but, aside from that, we should be mapping all power plants in order of ecological crisis potential, petro-chemical complexes, rail and inland shipping routes that will be affected, and so on and so forth. The price of human greed is far more costly that most people seem to be able to get their heads around. I am sure FEMA and other Federal Agencies will downplay the damage potential. The Lunatic Ward Case religious fanatics will want to jump on this with a chorus of blaming the other creed, the usual hate mongering will go on, as if a valid cause of a truly dangerous situation is needed. The simple answer, human greed is as usual. Could it be much simpler than that. Human greed in the van guard again. Some poor excuses for humanity on the world’s stock exchanges & bourses are already preparing some sort of derivative or other investment plan to profit from this. Thank you for being awake at the wheel. JCH
gbk,
“Strike-slip” was the exact term that was escaping me above. Thanks! 😀
Joy,
Lake Peigneur is stable at the moment, but there is steady seismic activity in the area. Most geologists familiar with it think it is a ticking time bomb.
If the main salt layer starts to dissolve, it will not be as rapid as a salt dome collapsing. From what I remember of Earth Science, the process would be kind of like digging the middle layer of a three-layer cake out with a spoon. After a while, the top layer would end up in direct contact with the bottom layer because the middle would be gone. In the meantime, the area would be riddled with hundreds of holes full of water but no bottom.
The New Madrid faults were caused by partial rifting of the North American plate during the break-up of Rodina (c. 700-800 mya.) The rebounding after the last ice age has possibly contributed to their becoming weaker, though glacial ice did not extend much past what is currently southern Illinois.
The faults move in a strike-slip fashion, I believe. There is no subduction.
Wow. That’s really moving. Especially in geological terms.
The image date on Google Earth is last March. Compare the hole from last March with how it looked on the 22 and one week later on the 27th. You can use the road on top of the berm for an estimate of growth.
Flyover 8/22/13
http://www.youtube.com/watch?v=hQ3anxbYxmE&feature=share&list=UURi6D8S8okOdYsJ-39YOvJw
Flyover 8/27/13
OS, I was wondering about whether large areas of land would sink if the salt layer – the purple layer in the first graphic at http://geology.com/stories/13/salt-domes/ – also collapses. It does seem possible that we could lose a substantial portion of Louisiana.
Has the Lake Peigneur sinkhole stablized?
Hmmm. Hadn’t considered the fault angle. But I think those faults are stress faults created at the end of the last ice age by glacial retreat and not subduction faults. Over time, the energy they release is decreasing further to the south moving northward. I can see where changing hydrology could change the stress dynamics though. I just didn’t think they stretched much further south than Arkansas.
Thanks shortfinals. One of the other videos put up by the Parish show one of the workmen using a reel type sounding line. No “Mark Twain” there. He ran out at least a thousand feet of cable and it was still dangling loose in the water. That damn pond wasn’t even there until this time last year.
Those guys working the scene are brave souls. They all know about the collapse of the dome at Lake Peigneur and the 150 foot whirlpool big enough to suck cargo barges down. That hole could give way as fast as the one that ate that factory in China.
Thanks Mike and JoF,
Here is something else to chew on. The mean height above sea level of the state of Louisiana is 100 feet. The highest point in the state is about 500 feet above MSL (mean sea level).
Look at a map of Mississippi. I used to fly in and out of the airports at Jackson. They are between 250 and 300 feet MSL. If you go to Google Earth and hover around the area, you will see that a large part of Assumption Parish is only a few feet above sea level. Copy and paste these coordinates into the Google Earth searchbar. Look down at the bottom right hand corner of your screen and you will see the height above sea level of wherever you hover the cursor. You will see that Bayou Corne is exactly one foot above sea level.
30°00’43.55″ N 91°08’18.38″ W
In the UK, the salt deposits in Cheshire (laid down in the Triassic), were extracted using hot water pumped into the strata, but this ceased after land subsidence began. Salt domes are – potentially – exceedingly fragile. Looks like we might be in the process of creating a new Salton Sea, this time with its own built-in pollution
Hello OS, Seeing recent news video of cypress trees sinking straight down into the water at the Assumption Parish sinkhole just boggled my brain. I had never even heard of salt domes prior to that, and I appreciate your explanation of this phenomenon. Very well done.
Chuck,
Nice work. You provide me with something I’ve never known, or heard of and manage to frighten me as well. Given that we’re both old guys, we csn well understand how much change occurs in a world over 50 or 60 years. What most of us haven’t fully experienced though is how the physical world around us can change so drastically. If this erosion of the salt dome continues we may lose 3/4 of a State or more. Humans, who see themselves hubristically as “Masters of the Planet” are not much in fact when compared with the forces of nature. Yet instead of trying to shape our activities to work with natural forces, we exploit them at our peril. This planet will be here long after we are gone.
The sinkhole needs to be privatized so that the Deep Sea Fishing industry can have offer trips without the customers having to leave dry land, so too speak. That hole’s going to get big enough to stock it with marlin, and tuna, and Great White Sharks and stuff. Maybe even move the Sea World whales there so they can have their own little ocean instead of being all cooped up. They can even have naming contests! My entry will be, La Mer Louisiane!
Squeeky Fromm
Girl Reporter