Bennie, S.L.; Stagpoole, V.M. 1985 Waterborne resistivity measurements in the Rotorua Lakes area of New Zealand. Wellington: DSIR, Geophysics Division. Report / Geophysics Division 206 40 p.
Abstract: Waterborne d.c. electrical resistivity measurements have been made on Lakes Ohakuri, Okareka, Okataina, Rotokakahi, Rotomahana, Rotorua, Tarawera and Whakamaru. The measurements were made using a Schlumberger type electrode configuration in which the potential electrodes were placed on the lake bottom, and the current electrodes were either on the lake bottom (1972 survey) or suspended from buoys floating on the surface (1982-84 surveys). The effect of the water above the electrodes, on the equivalent surface apparent resistivity, is everywhere sufficiently small to be regarded as negligible. The measured apparent resistivities, shown in the figures are also a good estimate of the average resistivity below the lake in all lakes measured but one. In Lake Rotomahana, in which the water has an unusually low resistivity (7 ohm m) the uncorrected values cold be a considerable underestimate of the resistivity of the material below the lake. The compatibility of waterborne resistivity measurements with those made on land was tested at Lake Whakamaru. Good agreement was found between measurements made on the lake and those of two adjacent, parallel traverses. The waterborne measurements have identified previously unknown areas of low resistivity in the north-western part of Lake Rotorua, the northern part of Lake Tarawera, and at the southern end of Lake Okataina. In addition the measurements have defined extensions of resistivity lows associated with the Rotorua, Orakeikorako and Waimangu geothermal areas. (auth)
