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

than the tails, the curve is excessively “peaked” (Boggs, 1995). If, on the other hand, the tails
are better sorted than central portion, the curve is “flat-peaked” (Boggs, 1995). The geological
significance of kurtosis is unknown and many believe it has little value in interpretive grain size
statistics (Boggs, 1995). Others believe that kurtosis is related to hydrodynamics and is a good
indicator of energy levels and wave height (Doeglas, 1946; Haan, 1977; Tanner, 1990). They
believe that the factors that can alter the hydrodynamic regime of an area and, thus, kurtosis,
include sea-level rise, seasonal changes and storm tide and wave impact events. According to
Tanner (1990) kurtosis values close to 3.0 are indicative of high-energy environments with large
wave heights. Tanner (1990) stated that kurtosis values of 4.0 and higher are indicative of low
energy environments with smaller wave heights. Where wave energies are low, kurtosis may be
a useful tool for estimating changes in ancient sea-level (Tanner, 1990). In general, the kurtosis
values for the east coast of Florida range from 3.0 to 3.5 (Balsillie, 1995). The lower Gulf coast
has kurtosis values on the order of 3.5 or greater (Balsillie, 1995). Kurtosis differs between these
two regions because waves are higher along the east coast than the lower Gulf coast.
For the panhandle coast wave heights and energy are low. Therefore, following Tanner’s
reasoning, kurtosis values should be high. The St. Vincent Island data obtained in this
investigation supports this assumption. Kurtosis values are high, ranging from 3 to 9 (Table 4.4).
If kurtosis is related to wave energy, the trends seen could suggest that the most recent beach
ridge sets (sets G, H, I, J, K and L) on St. Vincent Island, which encompass the past 2,000 years
or so, were formed during a time of higher wave energy while the older ridges (Sets A, B, C, D,
E and F) were formed during a time when wave energy was lower than it is today (Table 4.4).
This trend was also seen in the mean grain size and standard deviation results. Since the
formation of the oldest set of beach ridges approximately 4,000 years ago (Table 4.6), wave
energy has increased to modern levels. This increase in energy could be related to sea level
change. As a general rule, as sea level increases, wave energy should also increase. This
follows the Bruun Rule, which states that as the nearshore water depth is increased, more wave
energy is brought to the beach face (Douglas et al., 2001). These changes in energy, and
potentially in sea level, can be seen in the sediment characteristics of St. Vincent Island,
particularly in the mean grain size, standard deviation and kurtosis. These changes in energy
could also be related to an increase in storm frequency related to a changing climate.
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