Hey everyone, below is part of the introduction I wrote for a research paper over barrier island formations and vibracoring in my marine geology lab. If you'd like to read the full paper please let me know and I will post it. The format of this paper is strictly as my professor wanted it so if it looks odd to you, I apologize.
Also, I don't know how to indent with markdown. :/
Barrier islands are bodies of sand that are parallel to the shore; they front 10% of the world’s coastlines and typically have lagoons, backbarrier marshes, or tidal flats behind (Deaton et al, 2017). The barrier island and its backing offer natural protection to coastal environments from storms and sea level change. Sea level change is a direct threat to coastal lands and communities (Agboola and Ayanlade, 2016). Barrier islands and sea level change need to be studied because of how important it is to protect our coastlines from a change in sea level and from storms. Sea level change can affect the economy by destroying property through floods or hurting fisheries by lowering/raising sea level, which could cause the fisheries to lose their main catch. It would be beneficial to further understand barrier islands’ formation and composition to potentially create synthetic barrier islands with almost the same composition so more of the coastlines around the world would have this protection from storms and sea level change. By studying relative sea level rise, one could potentially improve and protect already formed barrier islands as well as future barrier islands.
There are three separate processes for barrier island formation: an emerged bar, a breached spit, and a sea level rise over a dune system. Bar emergence happens due to aggradation, which is when sediment is deposited vertically faster than sea level can rise. This aggradation is then built into an island. Breached spits occur when seawater forces its way through a spit and separates it from the mainland, this leaves part of the spit offshore. This offshore portion of the spit is the barrier island Dune system flooding is a result of sea level rising and flooding a dune system before receding. Once this flooding has occurred the water is trapped in the dune system and eventually separates the dunes from the mainland. This separation turns the dune into a barrier island.
Barrier island systems are prone to migration. This migration can occur due to a few reasons: longshore current, sea-level change, storms, tides, and waves. The migration is typically landward, however, progradation can occur in barrier islands. Progradation is when sediment deposition is greater than erosion and builds the formation seaward. Barrier island migration is landward when sea-level rises, storms cause overwash, tides cause overwash, and when waves cause overwash. Overwash is when water picks up sediment and deposits the sediment behind the coastal feature (Barrier Island) due to a rise in water level via storms, tides, or overall sea-level rise.
Barrier islands systems follow stratigraphic laws throughout their entire existence. Some of the stratigraphic laws that barrier island systems follow are: superposition, original horizontality, and lateral continuity. The law of superposition states that the newer sediments will be deposited atop the older sediments. The law of original horizontality states that all sediment layers were deposited horizontally and if they are no longer horizontal, they have been tilted. The law or lateral continuity states that sedimentary layers are continuous across large areas.
Sea-level change can be determined once the depositional environment is determined. Different depositional environments are found at different elevations regarding sea-level. Forests, overwash fans, and dunes are found above sea-level. Marshes, beaches, tidal creeks, and swamps are all found below sea-level. This information allows depositional environments from the past to be used to determine where sea-level was at during that time.
Typically, barrier islands consist of 5 different sections: a shoreface, a marsh that is divided by a tidal creek, estuary, or lagoon, a forest area, and an ebb-tide delta respectively. Barrier islands can form in a wave-dominated or a mixed-energy environment. Barrier islands formed in wave-dominated environments are long, narrow and have with a small ebb-tidal delta. The longshore current’s deposition of sediments is why the wave-dominated barrier island has the properties it has. Mixed-energy barrier islands are typically shorter, wider, and have higher lands with more inlets than wave-dominated islands due to wave-dominated islands’ inlets being closed from the longshore current’s deposition of sediment. Wave-dominated islands are normally lower than mixed-energy islands. Mixed-energy islands can develop a “drumstick” shape. This shape occurs when waves refract off of extended deltas and causes longshore currents to slightly reverse. This reversal deposits sediment on one end of the island which then, in turn, causes the island to develop the shape. South Carolina has wave-dominated barrier islands with all of the characteristics of a typical wave-dominated barrier island. The waves are smaller than normal due to South Carolina’s location on a passive margin.
Even though barrier islands can form through different processes, the stratigraphy of barrier islands has been observed to be similar (Davis et al., 2003). Studying the stratigraphic data of barrier islands can offer insight into past sea levels. Knowing past sea levels and examining the sediment can help researchers predict future how barrier islands will react to a change in sea level. With sea levels increasing at a steady rate barrier islands may eventually be non-existent as rising sea levels are able to overtake and destroy the islands.
Davis et al. (2003) studied the west-coast barrier complex in Florida to see how barrier islands form and how they develop overtime. To do this, 200 vibracore samples were extracted from the Florida Keys area and then examined in the lab. These cores were helpful in identifying relative Holocene sea-level in that area. The cores revealed 3 facies: well-sorted sand, shelly sand, shell gravel, and muddy shelly sand. Four subfacies were also identified: mud-laminated sand, muddy sand, and organic muddy. The facies and subfacies helped Davis et al. (2003) identify what the depositional environments were and where the relative sea-level was at that time.
Moore et al. (2014) studied barrier island systems in Louisiana, U.S.A. The researchers were studying the effects of sea-level rise and increasing strengths of hurricanes, due to climate change, on barrier island systems. They concluded that if the hurricanes keep coming in at greater strengths and if sea-level keeps rising at this steady pace that there would be no barrier islands in the Louisiana area in the near future. This extinction of Louisiana barrier islands would be due to the sediment supply not being able to meet the demand of the islands due to erosion from relative sea-level rise and storm systems.
The purpose of this study was to understand barrier islands in Murrell’s Inlet, South Carolina and use the data gathered from the stratigraphic data to see past relative sea levels. This data can be compared to other barrier island along the eastern coast of the United States and coasts along the world to get a better understanding of the eustatic sea levels from the past.
Image Source
Above is a picture to give a visual representation of barrier island systems.
ask for the rest of the paper
Sources:
Deaton, C. D., Hein, C. J., and Kirwan, M. L. (2016) Barrier island migration dominates ecogeomorphic feedbacks and drives salt marsh loss along the Virginia Atlantic Coast, USA. Geology Volume 45.2: Pages 123-26.
Agboola, A. M., & Ayanlade, A. (2016). Sea level rise and its potential impacts on coastal urban area: a case of eti-osa, Nigeria. Annals Of The University Of Oradea, Geography Series / Analele Universitatii Din Oradea, Seria Geografie, Volume 26(2), Pages 188-200.
Davis, R. A., Yale, K. E., Pekala, J. M., and Hamilton, M. V. (2003) Barrier island stratigraphy and Holocene history of west-central Florida. Marine Geology Volume 200.1-4, Pages 103-23.
Moore, L. J., Patsch, K., List, J. H., and Williams, S. J. (2014) The potential for sea-level-rise-induced barrier island loss: Insights from the Chandeleur Islands, Louisiana, USA. Marine Geology Volume: 355, Pages 244-59.
