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The geologic framework is an assessment of how the sediments were deposited in the area during the geologic past. The sedimentary layers below the lake bottom were imaged using a radar-like device called high-resolution seismic profiling. Sidescan-sonar images of the lake floor also were collected. These images are similar to aerial photographs of the land. Sediment samples were collected to analyze their composition and determine how they were deposited.
An evolutionary model (A-E, at right) for the Lake Pontchartrain area was developed using seismic and sedimentological data.Following the late Wisconsin sea-level lowstand (~18,000 years ago), sea level rose and flooded the area
(A-B). By 6,000 years ago, sea-level rise slowed, and longshore transport developed a barrier-beach system
(B). As sea level continued to rise, the barrier system was bypassed, forming the Pine Island Barrier trend, while flooding created the Pontchartrain Basin embayment (C). By 4,500 years ago, the Mississippi River moved into the area and began depositing the St.Bernard Delta lobe enclosing the embayment (D). Modern stabilization and subsidence of the delta lobe began by 2,000 years ago,developing Lakes Maurepas, Pontchartrain, and Borgne, and creating the land surface seen today.
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18,000 years ago
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6,000 years ago
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5,000 years ago
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4,500 - 2,000 years ago
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Present day
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U. S. Department of the Interior | U.S. Geological Survey
