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

Throughout the Holocene, the Apalachicola River and its delta have migrated in a
southeasterly direction (Donoghue and White, 1995). During periods of rapid sea-level rise, this
southerly migration was punctuated by retreats. As sea level rose through the Holocene, the
mouth of the Apalachicola River retreated northwards up the Apalachicola River Valley. This
movement has been the driving force behind the creation of relict quaternary shoreline features.
During the Quaternary, the Apalachicola River was the major sand source for the
Panhandle coast (Lamont et al., 1997; Donoghue, 1993). The Apalachicola River delivered
sediment at a rate faster than the coastal wave energy was able to dissipate it (Tanner, 1964). As
a result, the excess sediment load accumulated in the barrier islands, spits and shoals that now
rim the river’s mouth. From east to west the barrier islands include Dog Island, St. George
Island, Little St. George Island and St. Vincent Island (Figure 1.6). The shoals and barrier
islands in the region contain enough sand to account for the total sediment load of the river for
the past 5,000 years (Tanner, 1964). The relatively recent construction of dams across the river
has drastically reduced the amount of sediment being delivered to the coast (Tanner, 1964). The
development of the barrier island rim around the river’s mouth has also contributed to the
reduction in the amount of sediment by trapping much of the material before it reaches the Gulf
coast (Donoghue and Tanner, 1994).
Barrier Islands
Shore-parallel sediment deposits are common features on wave-dominated shorelines.
These deposits can occur as mainland-attached barriers, as strandplains consisting of multiple
parallel beach ridges or as barrier islands (Reinson, 1992).
Barrier islands are narrow, sand-dominated landforms that run parallel or semi-parallel to
mainland shorelines (Hoyt, 1967). They are usually separated from the mainland by a lagoon,
estuary or marsh system (Reinson, 1992). The stratigraphy and evolution of a barrier island is
influenced by several factors including sea level, sediment supply, pre-depositional topography,
tectonic setting and tidal range (Moslow, 1983).
Barrier island formation is a complex and poorly understood process. However, several
theories have been proposed in an attempt to explain their origin and formation. No single
theory has emerged as dominant. deBeaumont (1845) suggested that barrier islands form as a
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