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The Parengarenga Sandspit (Figure 1) is New Zealand's only coastal source of silica sand for glass manufacturing. Concerns about the environmental effects of sand extraction from the harbor mouth in the last two decades led the extraction companies to instigate a monitoring program. The Parengarenga beach-dune-monitoring program started in 1982; since that time cross-profiles have been surveyed twice a year from below chart datum (CD) to landward of the sparsely vegetated foredune system. This is the longest continuous record of beach profile measurement in New Zealand, and provides important information on the behavior of this coastal spit system (Parnell, 1997). The sedimentary material in Parengarenga Sandspit consists of 93.5% quartz and has a very uniform fine, sandy grain size (median 193 microns) from near shore to the beach and in the dunes.

Summary Ground-penetrating radar was used to study the stratigraphy and mode of development of a large solitary dune on a sandspit. Both dune and interdune flats are underlain by a Late Pleistocene paleosol. Radar images reveal three phases of dune development and together with the dune morphology point towards a combined star and transverse dune origin.