Faulting and Tectonic Subsidence on the Louisiana Coast – Goose Point

Also see: Faults

Haggar, K. S., 2014, Coastal land loss and landscape level plant community succession: An expected result of natural tectonic subsidence, fault movement, and sea level rise: Gulf Coast Association of Geological Societies Transactions, v. 64, p. 139–159.

Coastal Louisiana, and especially the lower Mississippi Delta, is being inundated by the ocean. The State of Louisiana has proposed a massive public works project to restore the coast. There is a massive lawsuit against the oil industry based on the theory that oil production is responsible for destroying a significant portion of the Mississippi Delta coastal wetlands. These restoration plans presume that the loss of the land is due to various human-driven causes which can be remedied, and that the high level of subsidence in the area is just a short-term phenomena that will not cause long term problems.

Goose Point (map) is a marsh area north of New Orleans. It is on an ancient Pleistocene plain, not river sediment. It has no water pumping or levees, no canals, no oil and gas production, or the other human-driven factors that are claimed to cause wetlands loss. Yet Goose Point displays the same patterns of land loss as regions of the delta. Goose Point, along with the rest of the Mississippi Delta, is very well characterized geologically. Goose Point is crossed by faults and is subject to tectonic subsidence, i.e., deep level subsidence that has nothing to do with compaction of river sediments. This deep subsidence and movement of fault blocks, combined with sea level rise, is sufficient to cause the typical land loss seen in Louisiana coastal wetlands.

The entire Delta is riven with faults and subject to tectonic subsidence. The faults have been well characterized because they provide traps for oil and gas. (Many oil and gas fields are located on faults. The faults cause the subsidence, not the extraction of hydrocarbons.) As Goose Point demonstrates, tectonic subsidence and faults, combined with sea level rise, are sufficient to cause characteristic wetlands loss without any of the traditional human-driven factors. This subsidence is long-term, as is sea level rise. This means restoration schemes based on mitigating human-driven factors will have little effect on the long term loss of the wetlands.