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

St. Vincent is a part. Based on a mass balance of sand, Stapor (1973) concluded that the barrier
island chain, including St. Vincent Island, is in a state of sedimentologic equilibrium.
Barrier Island Evolution Inferred from Beach Ridge Patterns
According to Stapor (1973) the direction toward which the beach ridge sets splay
(represented by the widest part of each set) indicates the transport direction of the longshore drift
cell that supplied the sand to build the beach ridge plain. If deposits are symmetric with little
splay they were likely constructed from offshore sand delivered directly to the beach without
significant longshore transport. The beach ridge sets on St. Vincent Island are shown in Figure
1.2. Sets A, B and C are symmetric with very little splay. This indicates that offshore sand was
moved directly from the inner shelf onto the growing beach ridge plain and did not undergo
significant longshore transport (Stapor, 1973). Sets D, E and F are tapered at the west end and
splay to the east. This suggests that the source of sediment for these ridges was located to the
east of the island and was transported to the beach ridge plain by westward longshore drift. Sets
G and K are not splayed, suggesting that they were a product of sediment being delivered
directly to the growing beach ridge plain. Sets H, I, J and L don’t follow any particular pattern.
Set I is splayed to the west indicating a reversal in drift direction. Set L splays northwest,
indicating that sediment was transported from the southeast. Sets H, I, J and L were likely
deposited as a result of the migration of the West Pass lunate bar across the inlet. Sets A through
D are thought to have been deposited when sea level was about 1.5 m lower than present (Stapor
and Tanner, 1977). After the deposition of these sets, sea level is interpreted to have risen
approximately 2 m (Campbell, 1986).
Each younger beach ridge set truncates the older ones. This is likely a result of
oscillating Holocene sea-level (Figure 2.3), which was responsible for fluctuations in volumes of
offshore sand available for supply to the shoreface (Stapor, 1973). A drop in sea level would
make additional sand available for erosion through the lowering of wave base (Stapor, 1973). A
rise in sea level could drive new sand shoreward for shoreface deposition (Stapor, 1973).
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