Friday, April 16, 2021

The History of Lake Pontchartrain's Shape

In 1968 Roger Saucier's  dissertation on the “Recent Geomorphic History of the Pontchartrain Basin” contained a wealth of information on the early shape of Lake Pontchartrain.

The research paper featured numerous outline diagrams of Lake Pontchartrain over the past several thousand years, how it had changed, plus details on Indian village sites and beach high ground that had been in the middle of the lake at one point in time.


 
Click on the images to make them larger. 

Of particular interest were the images of Milton's Island Beach Trend, which is now submerged under Lake Pontchartrain. Saucier reported that a shell dredging barge working in the area in 1934 pulled up a number of human and animal bones mixed in with its load of sand and shells. Humans apparently lived on the island hundreds of years ago.

Many maps showing the bottom of Lake Pontchartrain indicate a large shallow sandy area just south of Mandeville. This could be the remnants of the former Milton's Island.

Here are the most interesting diagrams in the document showing Lake Pontchartrain's changes in shape over the eons. Click on the images to make them larger. 

 
Lake Shape 3500 to 4000 Years Ago

 
 
Lake Shape 2600 to 2800 Years Ago


 Lake Shape from 2000 to 2400 Years Ago

 
Lake Shape 1400 to 1800 Years Ago

 
Lake Shape 300 to 500 Years Ago


 
Other Interesting Maps




 
Several thousand years ago, if you were to follow the flow of water down the Tchefuncte River, you'd be going southward to where the river joins that large body of water known as ....  The Gulf of Mexico. 




That is because at that time New Orleans wasn't there yet, and the big shelf of land that New Orleans would be built upon wasn't there yet either. The land hadn't yet been deposited by the tons of silt and sediment coming down the Mississippi River with each Spring flood. (Area 3 within the red outline). As the silt spread out from the end of the river, it curved around and closed in the east end of Lake Pontchartrain, which was, in the beginning, a large bay on the north shore of the Gulf of Mexico. 
 
Lake Pontchartrain retains a connection to the Gulf of Mexico through two tidal passes, the Rigolets and Chef Menteur Pass, and, therefore, is more accurately described as an estuarine embayment than a lake.

The Lake Pontchartrain Watershed. The U.S. Geological Survey, 1995
 


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