New Orleans sits atop an ancient barrier island

Updated: May. 22, 2017 at 4:18 PM CDT
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(WVUE) - To the casual observer, it looks like any other section of marsh.

However, this spot in extreme Eastern New Orleans - almost at the St. Tammany Parish line - is unique. The rare visitor can walk along an ancient sandy beach, in high tide just a sleeve of sand.

"If you go out to Ship Island, you're going to see sand and shells like this," said Richard Campanella, a Tulane University historical geographer who has written extensively about the city's architectural history. "Many New Orleanians might be surprised to hear that beneath their city runs a relic barrier island."

Centuries before New Orleans existed, what geographers have dubbed the Pine Island Trend looked very similar to Ship Island in Mississippi, Dauphin Island in Alabama, or even Grand Isle, Louisiana.

This now-subterranean feature ran from what is modern-day Metairie through Lakeview and Gentilly and followed part of the I-10 route before veering off to the southern tip of St. Tammany.

While the Mississippi River built most of South Louisiana, Campanella said the island owed its existence to the Pearl River.

Roughly 4500 years ago, he said the Pearl deposited sand in the gulf of Mexico during a period of slow sea-level rise. Longshore currents swept the shoal westward, "sculpting it into an island."

A couple of centuries later, the Mississippi jumped its channel near present-day Lafayette, lunged toward the east, and belched mountains of silt to build the areas around New Orleans.

"Today, 165,000 people live on top of this relic barrier island," Campanella said.

The feature came to the attention of geologists and geographers in 1937 after a team of engineers and architects started working with the Depression-era Works Progress Administration.

Campanella discovered an excerpt in the New Orleans Item-Tribune, describing soil samples and, "a fine white sand, mixed with sea
shells of various kinds and sizes, at varying depths of 1 to 15 feet below the surface."

Coastal geographer Roger T. Saucier dubbed it the Pine Island Trend.

In 2005, when Hurricane Katrina blew apart the London Avenue Canal levee, people on the east side of the canal were mystified as sand buried cars and lawns.

"That was excavated Pine Island Trend sand," Campanella said. "It tapped into this ancient, 4,000-year-old barrier island that many people had no idea existed."

In extreme Eastern New Orleans, he found the one spot where evidence of the island still exists at the surface. Just out of the river's reach, a sliver of sand and pine trees remains in the middle of a marsh. 
"If it weren't for this feature here, we would have a completely different southeastern Louisiana," he said.

Had it not been for Pine Island, Campanella explained the river would have flowed farther to the north, filling in a large part of Lake Pontchartrain and building a cypress swamp that probably would have resembled the Maurepas Swamp.

"Therefore, all of the thinking that went into citing the city would have happened elsewhere."

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