The Vanishing Islands: A Look at the Louisiana Coasts Barrier Island System Nicole BarryWestern Governors University

Origins One of the youngest geologic structures already in danger of vanishing. Formed in the Holocene Epoch apart of microtidal and mesotidal regimes( 4,000 to 6,000 years ago) upon the decline of rapid sea level rise and sea level stabilization.Clastic sedimentary marine depositsThe geologic mechanisms that formed barrier islands are still in question, though most recent findings coincide with spit-building processes.

1919 Theory (Johnson) - Influx of sediments

landward

Spits are breached by tidal action and separated from the

mainland forming a barrier island.

Sea level stabilizes and tidal actions rework

sediments into strips of exposed land

1962 TheoryErosional drift of sediment accretes down current of mainland forming spits A Decline in Rapid

Sea Level Rise Led To:

Barrier Islands and their Components:

Dunes - Mounds of sand crucial for stabilizing the barrier island and preventing erosion.

Wash-over - Inundation of the dunes by seawater resulting in run-off basin-ward through the sand flats. Exhibited morphology is of narrow-bands that expand into funnel-like areas for vegetation in thin laminate sheets (<2m). Isolated lenses of basal sediments from spit-formations are in units. Wash-overs gradually supersede existing flood deltas. Lagoon - Muddy waters , truncated areas from washover that become anoxic organic environments. Preserved units indicate impermeable mud, organic material bound by sand (see stratigraphic controls) that result in petroleum and coal deposits.

Flood Tidal Delta -Basinward deposit of sediments that reactivate in a transgressive environment causing higher rates of erosion.

Spits - Rare features known for their sediment accreting properties in rapid island building processes and proposed to have the primary role in barrier island creation. The littoral drift caused by an oblique angle of waves along with bioturbation of sediments forms these structures. In landward deposition, preserved currents can be found in units near the back-barrier. Steep to gentle stratification indicate both a landward and seaward dip with deposits consisting of shell fragments. ( elaborate on spatial trend, highest subsidence rates always at these locations)

“Outcrop of Mississippean barrier island tidal channels on Route 23 Kentucky at Pound Gap.” ( Woodworth, Mendenhall, Knight,

Shoreface - Where the ocean and barrier island come together. Shallow sandbar below the water line. Waves have lost their intensity and fossils are found as a result of bioturbation. Silt, mud, and fine sand are the sediments here Middle - No bioturbation as a result of varying wave intensity. Size of sand grains are large. Foreshore - An area of high and low tide where coarser sand allows for cross-bedding. Backshore - Above water where berms are located where wind dominates erosion.

“ Major Depositional Settings of Barrier Island Systems ” SEPM Sequence Stratigraphy Web

Barrier Island Mechanisms:

As Mother Natures first line of defense, barrier islands protect the mainland and the wetlands against storms. The USGS Geological Scale affect of storms to barrier islands can be assessed on an impact scale from 1-4. As a result of an Impact 4, duly noted as Hurricane Katrina, the barrier islands suffered severe net loss to land. They serve as system controls to wetland environments along with shielding pipelines and industry terminals from storms.

Back-barrier- An area that the barrier island separates from the ocean where many deposited units can be determined. There is a progradation trend in upper 6m of strata, where oldest to youngest deposits can further be separated. In their units a switch in stacking patterns can be identified, where the continental shelf space opens up and deposition is less, accommodating the shelf mudstone in the change of a microtidal regime. Barrier islands serve as a gateway in the exchange of sediments that pass through to flood tidal deltas and those that nourish the dunes of the islands.

HIGHLIGHTED FEATURE:

Current Conditions: Along with a receding Mississippi River Delta , transgressive migration (due to continental shelf subsidence), erosion and heavy storm impacts the barrier islands along the Louisiana Coast are in a crucial state of existence.

Timbalier Island - Known for its historical processes and the most morphological changes. Exhibits most land migration. Accretion on the west end as a result of island spit-building process causes lateral migration and shows to be the best means for rapid growth at the cost of erosion. Chandeleur Islands - Suffered devastating effects from Hurricane Katrina and the recent Deepwater Horizon oil spill.

Raccoon Island/Pass - Flood tidal inlet with diverse stratagraphic depositions and a transgressive trend. Its crossing with Timbalier Bay has led concurrent projects including beach nourishment. Underlying are buried remnants of Mississippi distribution channels that underwent a regressive event and are possibly the cause of high erosion rates. Currently, the shoreline of this barrier island is retreating.

Lafourche Spit - Cores taken from deposits here are unique in that they blend in with the flood-tidal sand-rich facies, though have a subtle identifiable feature to allow for further separation. It has been found that a bed of species, the Mulina, and fragments of them are living at the basal contact zone. A “hash horizon” about .25m thick capped with finer grain sediments is found in cores at this location.

A Google Earth Closer Look:Specific Features of Barrier Islands

Restoration:

Historical Distributaries of Mississippi River By Jakob Rosenweig, Tulane University

With closing of the Mississippi River Gulf Outlet Canal historical channels can be restored to nourish wetlandsIncrease plant cultivation on Hammock (forested) Islands Review and support those entities actively engaged in restoring the barrier islands.

Supporting Entities:

COAST 2050

LACoast.gov

OILTIDES.COM

Plant Cultivation: Specific species that are key to fostering a stable underlying system. Plants with key traits are described below:

Rosa Rugosa – Extremely tolerant to salt . Breed known as Roseraie de L’Haÿhas excellent rootwork properties. The United States Department of Agriculture (USDA) has listed plants to proliferate in the areas (as listed below right.)

Rosa rugosa buds on Grape Island, Massachusetts

The state of Louisiana is not highlighted in the USDA map of native status, though several states have similar wetland conditions that satisfy their growth in buffer zones. Rhode Island is such a state that has also had beach nourishment activities due to erosion.

Land Nourishment: Spit/Inlets have natural island building properties. Developing an adding to the growth of those spits near barrier islands may likely increase the chance of successful nourishment projects.

Spit/Inlet

“Stratigraphic Architecture of a Transgressive Tidal Inlet-Flood Tidal Delta System: Raccoon Pass, Louisiana” ( Kulp, M.A., Fitzgerald, D., Penland, S., Motti, J. Brown, J., Flocks, J., Miner, M., McCarty, P., Mobley, C.)