Chenier Plains

At Miranda you can see what some say is the finest example of an active shell and sand chenier plain anywhere in the world.

A chenier is a beach ridge resting on silty deposits which has become isolated from the shore by a band of tidal mudflats. A chenier plain consists of a series of cheniers separated by mudflats.

The Miranda-Kaiaua cheniers are first formed as sand and cockle-shell bars on the foreshore or intertidal flats. The bars are then moved landward by wave action. Eventually the bars attain sufficient height to withstand such wave action. Deposition of fine sediments also occurs in the embayment created on the landward side of the shell ridge. These sediments accumulate to such an elevation that mangroves and other saltmarsh plant species can colonize the area. Their stabilising roots assist in the accumulation of mud and a process of natural reclamation occurs, thus building up the plain.

Miranda coast 1988
A succession of 13 shell ridges is recognisable on the 2km-wide coastal plain that has built out from the old cliff-line around Miranda in the few thousand years since the seas level rose after the end of the last ice age. The cheniers range from less than one metre to a little over two metres in height, from 20 to more than 100 metres wide, and 0.5 to 4 kilometres in length. The oldest ridges at the back of the plain are a metre or so higher than those near the modern shore. Shells within the old ridges have been carbon-dated to determine their various ages. Results show that 3900 years ago the sea level was 80cm higher than today. It fell gradually until 1200 years ago, and since then has remained relatively steady at its present height.
Miranda Coast 1996
More detail on chenier plains