Tropical cyclones - Extreme Events: A Physical Reconstruction and Risk Assessment - page 86

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0 Distance (m) from shore 200 400

Figure 4.3. Stratigraphy and chronology for a coral shingle ridge sequence at
Curacoa Island, Central Great Barrier Reef, Australia (from Nott and Hayne, 2001 ).
Note theprogressively increasing age of ridges with distance inland. Radiocarbon
ages are mean (uncalibrated), marine reservoir corrected. See Nott and Hayne ( 2001 )
for uncertainty margins for each age.

sediments are deposited by surge and/or waves. Substantial quantities of sedi-
ment, mainly sand and occasionally isolated shells, can be transported inland
and deposited by the high velocity winds of tropical cyclones. These deposits are
difficult to recognise as they often occur in sedimentary environments where
similar sand sized particles are deposited by normal aeolian processes.

Coral rubble/shingle ridges

Coral rubble ridges occur in locations where coral reefs occur close to
shore. During the tempest, coral fragments are eroded from near-shore reefs
by wave action and transported either onshore or offshore (Baines et al ., 1974;
Davies, 1983;Hughes, 1999;Rasserand Riegl, 2002). Fragments can also be trans-
ported from existing accumulations of coral rubble in the offshore zone. These
offshore accumulations result from a number of erosional processes such as
biodegradation and wave action during both storms and fair weather condition
(Rasser and Riegl, 2002;Hughes, 1999). It is thought that the angle of the off-
shore reef slope plays a role in whether the eroded fragments are transported
predominantly offshore or onshore. Steep reef fore-slopes favour offshore trans-
port of fragments, often to depths of greater than 50 m which is too deep
to be reworked and transported by storm waves. Shallow sloping, and partic-
ularly wide, reef fronts favour transport onshore and the formation of coral
rubble ridges. However, some sites, such as Curacoa Island in the central Great
Barrier Reef, Australia (Fig. 4.3)that are fronted by narrow, steep reef slopes have
extensive coral rubble ridge development on land (Hayne and Chappell, 2001;
Nott and Hayne, 2001). These sites with presumably minimal accumulation of