The geology and hydrology of Niue Island, South Pacific

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Schofield, J.C. 1959 The geology and hydrology of Niue Island, South Pacific. Wellington: Government Printer. New Zealand Geological Survey bulletin 62 27 p.

Abstract: Niue or Savage Island consists solely of limestone in the form of emerged reefs forming terraces at 180-215, 65-80, 40-45 ft and possibly another at 115-130 ft. A fringing reef at low-tide level is most often backed by a wave-cut platform. Submerged terraces occur at -36 to -48 and -108 to -120 ft. These are thought to have formed during Pleistocene stillstands of sea level of 215 to 235, 115 to 130, 75, 40 to 45, -36 to -48, and -108 to -120 ft. The uppermost reef terrace encloses a central basin interpreted as a former lagoon. A magnetic survey of the island shows that the limestone is underlain by a caldera-shaped, presumably volcanic substructure. Niue soils consist of residue from weathered limestone; alumina to phosphate ratios suggest that residues of volcanic ash may also be present. The original ash was probably basic. Magnesium enrichment is greatest under lagoonal conditions. On the coast it has taken place, not only at the intertidal zone, but possibly also at levels 20 to 60 ft below sea level at the same time. Fresh ground water probably consists of a lens afloat on sea water. The freshwater-saltwater interface extends up to the water table near the coast. Inland, the water level in the one well and several resistivity-derived levels show that the water table rises to about 10 ft above mean sea level. In the well, which is 1 ¼ miles from the coast, the water table normally fluctuates 2 in at tidal intervals. (auth)