Sand Beach Ridges

South of Cairns on the east coast of Cape York Peninsula a sequence of 29 shore parallel coarse-grained sand ridges occurs at Cowley Beach. These ridges have been dated using optically stimulated luminescence (OSL) and they span the past 5,500 years with an average interval between ridge emplacement of 260 years (Fig. 7 and 8, Nott et al., in prep). These ridges also rise to approximately 5 m AHD and they extend alongshore for several kilometers. Like Pormpuraaw, there are no

Fig. 5 Aerial photo of beach ridge sequence at Pormpuraaw. Distance from shore to inland extent in photo is approximately 3 km

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Distance from shore (m)

Fig. 6 Topography and chronology of sand/shell ridges at Pormpuraaw

Fig. 7 Oblique aerial view of sand ridges at Cowley Beach. Ridge crest are dominated by darker vegetation (Photo D. Hopley)

coral reefs close to shore at this location so coral fragments are absent within the ridges. Here, shell production is much lower in the inshore zone compared to Pormpuraaw and marine shells are sparse within these ridges. The local stream (Liverpool Creek) entering the sea near Cowley Beach drains a granite and meta-morphic hinterland and has dissected a broad valley infilled with late Pleistocene

fluvial terraces composed predominantly of coarse-grained sands. It is this material that has been the source of sediment to the nearshore coastal environment and which is exposed on the beach face at Cowley Beach following storms.

Several other sand beach ridge sequences also occur along the northeast coast of Australia where multiple beach ridges parallel the coast. Over 30 Holocene ridges rising to 4-5 m AHD occur near the Haughton River south of Townsville. Here the ridges are composed of fine to medium grained sands. Given that landforms composed of sands of this texture can be eolian in origin it is difficult to be as confident that these ridges were emplaced by tropical cyclone generated storm tides and waves. However, like Cowley Beach this is the only material available in the nearshore environment for transportation by waves.

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