The Formation of Deflation Ridges

The deposition of both pumice and shell is common on beaches during calm and storm wave conditions. This paper describes an investigation of pumice and shell ridges at two sites in Australia, Dark Point in NSW, and in the Younghusband Peninsula in SE South Australia. The formation of lines of wave formed shelly and pumice rich deposits on, and above the backshore is described. The deposits are buried by dune development, but then later exhumed by aeolian deflation as deflation plains and basins evolve. Aeolian erosion of the finer sandy sediments leads to the creation of a ridge form, herein termed a deflation ridge. A new schematic model of ridge formation is also detailed whereby deflation ridges are formed by the aeolian erosion and deflation of shell or pumice concentrations and lag deposits.