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Fort Proctor, a pre-Civil War fortress near Shell Beach in St. Bernard Parish, is subject to an assault in cannot repel.
This one comes from nature, and specifically, from below as the fort and the land surrounding it crumble.
“It represents so much about our past, and unfortunately, so much about our future,” said Bill Hyland, the St. Bernard Parish Historian.
At first glance, it might seem the land that once surrounded the fort simply eroded.
However, geologist Chris McLindon offers another explanation.
McLindon, a past president of the New Orleans Geological Survey who has become active in coastal issues, says the fort was probably built four or five feet above sea level.
“The foundation is now two feet below sea level,” McLindon said.
McLindon points out the fort happens to sit next to a NOAA Continuously Operating Reference Station (CORS), which provides data in support of three dimension positioning.
The CORPS station measures subsidence in real time.
Based partly on the data, McLindon believes the fort and the land surrounding it sank by six-to-seven feet over time.
Subsidence is hardly a new phenomenon in the delta.
“We have deposits of the Mississippi River that are three miles below the surface today and that’s a measure of subsidence over a very long period of time,” McLindon said.
During the last ice age, glaciers stretched as far south as Illinois.
As that miles-thick ice retreated 10,000 years ago, geologists say an almost unfathomable amount of mud and sand flowed south through the ancient Mississippi River.
“If you think of the Himalayas with Mount Everest five miles tall, the sediment accumulated from the Mississippi River since it first came into South Louisiana is five miles deep.”
That was before the river started sculpting South Louisiana as we know it today over several thousand years, belching its load of sand and mud before darting off on another course.
New deltas formed– sometimes on top of old, sinking deltas– along with natural faults below the surface.
Many scientists blame three dozen different factors for the loss of the coast, from salt water intrusion moving through oil and gas canals to subsidence due to the extraction of ground water and petroleum.
However, McLindon, an oil industry geologist, argues subsidence along those fault lines played a critical role in during the 1970s.
“The research that’s been done over the last few years is beginning to show pretty clearly that most hot spots of land loss are hot spots of subsidence,” McLindon said.
Industry geologists witness the effects daily on their computer screens as they probe for oil and gas deposits on seismic data, sort of a sonogram of the earth.
The New Orleans Geological Society, university professors, and the Louisiana Geological Survey are putting together an underground atlas of South Louisiana, partly to pinpoint the locations of faults.
Knowing that could help prevent planners from dumping millions of dollars into some future coastal project only to see the land sink.
“Subsidence is a huge factor in land loss in Louisiana,” said Bren Haase, head of planning for the Louisiana Coastal Protection and Restoration Authority. “So, we absolutely can’t ignore that.”
Haase welcomes the work on the atlas, but adds the state already factors that kind of data into planning.
“I know of at least one project where we made a decision to relocate it based on the fact that we thought there was perhaps a fault,” Haase said.
Geologists have identified 16 different Mississippi River deltas dating back 5,500 years.
In a perfectly natural system, with the river free of levees and periodically changing course, McLindon said there would be no-net land loss. Parts of the delta would erode as the river abandoned them and as new deltas formed elsewhere along the coast.
“The changes that are happening in South Louisiana are just outside our perception,” McLindon said. “They happen at a rate that’s slow enough that we don’t really perceive them on a day-to-day basis.”
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