Beach Sands on the West Coast, North Island

The study provided regional scale data on “the relationship between texture, composition and distribution of beach sediments relative to their source materials and the transport and depositional processes affecting them”. Results of the study indicate that ironsand deposits are primarily derived from volcanic rock sources, mostly from Mt Taranaki, with secondary input from the TVZ via Waikato River. Rivers are the primary means of transporting sediment to the coast. The thesis concludes that the West coast littoral system is regional in scale but the overall system contains discrete zones of heavy mineral rich sands, related to changing mineral composition of the beach sands which is driven by wave activity. Lighter minerals are transported more easily and become more abundant with distance north along the coast. The grain size of sediment on the beaches becomes finer both to the north and the south of Taranaki, with localised patches of coarse material appearing along the way. The overall picture is of a continuous conveyer belt moving to the north from Cape Egmont. This project was undertaken in conjunction with the “coastal sediment movement and storage” FRST programme www.niwa.cri.nz; undertaken by NIWA and run over a period of 18 months from August 1998 to February 2000. Purpose: The focus of project was to determine the dispersal and origin of beach sands along the West coast of the North Island, using petrographic techniques. This project also considered whether the west coast littoral drift system is a “river of sand” or whether there isolated beach compartments with discrete zones of sediment transport.

Took beach samples from mid-tide level (over six hour period around mid-tide) at 5 km intervals along the west coast of the North Island. Also collected representative samples of sand carried in the bed load of major rivers draining into the field region. These river samples were gathered to determine whether sands seen on the beach reflect the composition of the source rock. Sample numbers and locations (Lat-Long) given in Appendix A. All mineralogical data given in table in Appendices B-F. Appendix C: Visual estimates of mineralogy – expressed as % of total minerals present. Total opaques, Augite, Hornblende, Hypersthene, oxyhornblende, zircon, orthoclase, microcline, other (silicates), other (lights), chlorite, plagioclase, quartz, glass, CaCo3 and other descriptions. Appendix D: Point Count data, presented as % total of 250 point counts. Appendix E: Visual estimates of River sediment mineralogy. Appendix F: X-ray diffraction data of ninety mile beach sand samples. Median and mean grain size and description of location given in Appendix G.

Numerous beaches on the western coast of the North Island.

Sediment samples collected between November 1998 and September 1999 (Waikato samples March 1999). River sampling September 1999.

Sediment samples collected using a core sampler 3 cm diameter by 10 cm long. Samples analysed including mineralogy, point counting, and X-Ray diffraction analysis. Locations fixed with GPS. Sediment samples analysed at NIWA with Galai (as a separate part of the study).

Printed copies of all data in theses appendices. Digital Format: No data stored digitally in thesis. Data may be available from NIWA.

MSc thesis, part of the “coastal sediment movement and storage” FRST programme www.niwa.cri.nz; undertaken by NIWA and run over a period of 18 months from August 1998 to February 2000.

None known

Dataset complete