Tropical cyclones - Extreme Events: A Physical Reconstruction and Risk Assessment - page 94

Figure 4.8. Toeofasand sheet deposited after denuding sand dunes during
Tropical Cyclone Vance. Note the sedimentary structures (cross-bedded foresets,
arrowed) in the foreground where the ridge has been excavated.
tsunami. The available literature suggests that tsunami sand splays are some-
times structureless, or have horizontal bedding, or have cross-beds indicating
bi-directional flow (Goff et al ., 1998). The Tubridgi Point sand splay from TC Vance
differs in having tabular cross-beds suggesting uni-directional flow (Fig. 4.8).
Whether these different styles of sedimentation bear any specific relationship
to tsunami versus storm wave processes, however, remains to be ascertained.
Washover deposits
The deposition of sand layers, up to tens of centimetres thick, in back
barrier lagoons and swamps where fine-grained sediments are usually deposited,
has been interpreted as evidence of storm washover events. Sediments within
back-barrier lagoons are normally muddy, organic or fine grained. Interbedded
sand layers within these fine-grained sediments can be due to storm surge and
wavesovertopping a sand-dune barrier, and transporting sand into an environ-
ment where it is not normally deposited. By geologically dating the sand layers
along-term history of cyclones in a region can be ascertained. It is important