the florida state university college of arts and sciences evolution of ...

esult of the buildup of offshore bars. Waves approaching the shore stir up sea floor sediment.
When these waves break, they lose energy and the sediment accumulates forming a bar and
subsequently an island. Gilbert (1885) suggested that the material that forms a bar is transported
along the shore by littoral and longshore currents rather than coming from the seafloor as
deBeaumont (1845) suggested. These sediments accumulate to form a spit. The spit is then
breached and as a result of this breach, a barrier island is formed. Zenkovitch (1962) suggested
that barrier islands are a product of the sinking of wave-built terraces or the submergence of
alluvial plains. Price (1963) proposed that small barriers form as a result of storm wave activity.
Leontyev and Nikiforov (1966) suggested that barrier islands form from offshore bars exposed
during a lowering of sea level. Hoyt (1967) hypothesized that a barrier island is formed by the
building of a ridge immediately landward of the shoreline from wind or water deposited
sediments. Slow submergence floods the area landward of the ridge, forming a barrier and a
lagoon.
Although many models have been proposed to explain barrier island formation, three
models are commonly encountered in the literature; 1) the upbuilding of offshore bars, 2) the
cutting of inlets through spits and 3) the submergence of ridge like coastal features (Schwartz,
1971). The first model is based on the aggradation and emergence of submarine bars
(Zenkovich, 1967). This model suggests that a barrier island is formed when an offshore bar
builds up to the water surface. This theory is generally rejected because to form barrier islands
in this manner, the submarine bar would have to build up through the surf zone, which is
unlikely because wave action in the surf zone would wash away the crest of the bar and prevent
its emergence. The second model is spit progradation parallel to the coast and segmentation of
the spit by channels (Fisher, 1968). This is similar to the theory proposed by Gilbert (1885).
The third model is that barrier islands are formed by the isolation of beach and dune complexes
due to coastal submergence (Hoyt, 1967). This last theory is the most feasible. However, it is
most likely that extensive barrier island chains have had a composite mode of origin, both by spit
progradation and by coastal submergence (Reinson, 1992).
Barrier islands are dynamic systems that migrate landward in response to sea-level rise,
subsidence or a reduction in sediment supply (Lamont et al., 1997). Most modern barrier islands
have migrated landward in response to the Holocene transgression (Reinson, 1992). Barrier
islands are abundant along the Gulf of Mexico coast. Barrier island nuclei in the Gulf were most
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