Geology Reference
In-Depth Information
A tale of two storms: an integrated fi eld, remote sensing and
modelling study examining the impact of hurricanes Frances
and Jeanne on carbonate systems, Bahamas
STACY L. REEDER
*†
and EUGENE C. RANKEY
*‡
*
Comparative Sedimentology Laboratory and Center for Southeastern Tropical Advanced Remote Sensing
Rosenstiel School of Marine and Atmospheric Science University of Miami, Miami, FL 33149, USA
†
Schlumberger-Doll Research, One Hampshire Street, Cambridge, MA, 02139 (E-mail: sreeder@slb.com)
‡
Department of Geology, University of Kansas, Lawrence, KS, 66045
ABSTRACT
Tropical cyclones are commonly cited as being infl uential, or even dominant, controls
on the geomorphological evolution of carbonate systems, and their infl uence is high-
lighted in many interpretations of ancient platforms. A unique opportunity to explore
the effects of storms on platform systems occurred when two strong tropical cyclones
(Frances and Jeanne) passed directly over the shoals and reefs of the Abacos, northern
Bahamas, in 2004. Observations of the infl uence of these storms coupled with hydro-
dynamic observations and wave models provide insights into the nature and extent of
geomorphological change that might be related to the passage of such storms.
Comparisons of high resolution (2.4 m pixels) QuickBird remote sensing images
and modelling lead to a conclusion that storms have spatially limited effects on the
subtidal platform and shoals, and that storms are neither suffi cient to alter the system
nor necessary for lobate shoals to form. Instead, daily processes (winds, waves and
tides) produce conditions adequate to explain geomorphological features.
The effects of these two storms are not enough to explain the geomorphological evolu-
tion of this tidally infl uenced system. Other studies show that storms had comparable
impacts, suggesting that this is not an exceptional case. These observations are consis-
tent with a quantitative wave model showing the distribution of energy across carbonate
systems with different geometries. These observations and model results highlight the
diffi culty of generating grainy 'storm deposits' of comparable extent to those interpreted
in some ancient successions. Collectively, these observations and models question the
paradigm of storm infl uence on shallow-water carbonate platform geomorphology.
Keywords
Storms, hurricanes, waves, carbonate sedimentology, geomorphology,
Bahamas, tidal deltas, ooid shoals.
INTRODUCTION
studies highlight interpretations of 'storm-
dominated platforms' and 'storm wave base'
(reviews by Ager, 1981; Aigner, 1985; Pomar,
2001). At a smaller scale, many lobate features on
Holocene platforms were originally described as
'spillover lobes' (Ball, 1967) with a morphology
interpreted to be driven mainly by storms (Hine,
1977). Nonetheless, although storms frequently
traverse carbonate platforms, direct observations
of major storm impacts on carbonate platforms
are relatively rare (Major
et al
., 1996). In fact,
some studies have illustrated the lack of impact
of storms on carbonate systems (Boss & Neumann,
1993; Rankey
et al
., 2004).
The passage of two tropical cyclones (Hurricanes
Frances and Jeanne) over the same area on Little
Tropical cyclones are commonly invoked as
signifi cant geomorphological and geological forces
that shape carbonate sedimentary systems (Ball,
1967; Perkins & Enos, 1968; Wanless
et al
., 1988;
Scoffi n, 1993; Wanless & Tedesco, 1993) due to
their powerful forces including excessive wind
speeds, increased current velocities, storm surges
and a broader higher-energy wave spectrum. In
many ancient carbonate successions, thin, but
apparently laterally extensive, grainy beds have
been interpreted as storm-generated deposits
(Kreisa, 1981; Seilacher & Aigner, 1991; Aigner,
1982, 1985; Kreisa & Bambach, 1982; Jennette &
Pryor, 1993). Additionally, many stratigraphic
