Coastal Classification Atlas

Geologic Setting

The southeastern coast of Louisiana between Pass Abel and East Timbalier Island consists generally of two sandy barrier islands and a headland with narrow sandy beaches overlying muddy delta plain marsh deposits. Grand Terre Island is the western remnant of a larger barrier that was breached by opening of Pass Abel sometime between 1884 and 1932 (McBride and others, 1992). The second and largest barrier island, Grand Isle, has numerous beach ridges on its northeastern end that record abundant sand supply and advancement of the Gulf shoreline when it formed about a thousand years ago. A prominent physiographic feature is the Caminada-Moreau headland that encompasses a complex of arcuate beach ridges surrounded by saline marshes. West of the beach-ridge complex the headland is characterized by a broad flat delta plain marsh. The rapid erosion, absence of dunes, and low elevation of this coastal segment make it vulnerable to frequent inundation and overwash (Penland and Ritchie, 1979). The beach sand along this coastal segment typically contains some broken shell as a result of high rates of beach erosion and associated wave reworking of the underlying bay-estuarine deposits.

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