New Zealand Journal of Marine and Freshwater Research abstracts

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EVIDENCE FOR SUBMARINE GEOTHERMAL ACTIVITY IN THE BAY OF PLENTY

A. R. Duncan

New Zealand Oceanographic Institute, DSIR, Wellington

H. M. Pantin*

New Zealand Oceanographic Institute, DSIR, Wellington Abstract Gas bubbles rising to the sea surface and unusual scattering zones on echo-sounding records provide evidence for areas of submarine geothermal activity near Whale Island and White Island.

The Taupo Volcanic Zone extends off shore in the Bay of Plenty at least as far north as White Island. Several islands in the Bay are associated with Pleistocene or Recent volcanism; and White Island, Whale Island and the Rurima Rocks (J. W. Brodie, pers. comm.) have active geothermal areas.

Two areas in which bubbles can be seen, rising to the sea surface, one north and one south of Whale Island, have been brought to our attention by Mr E. G. McCracken and Mr R. G. Butler, of Whakatane. The concentration of bubbles in the sea water is low and variable; and the bubbles can only be observed in calm weather. For this reason the location and size of the bubble areas described below and shown in Fig. 1 are only approximate.

The southern bubble area is centered 2 km SSW of the eastern end of Whale island at 37° 52.9'S, 176° 58.7'E, and is elongated NNE-SSW with a length of 3 km and a width of 1.5 km. The bubbles are generally a few millimetres in diameter and usually occur in groups with individual bubbles a few centimetres apart. The diameter of a bubble group is between 10 cm and 1 m, and within an area of 10 m² such a group appears at intervals of between 10 seconds and 2 minutes. The northern bubble area is centered 5 km NNE of the eastern end of Whale Island at 37° 48.9'S, 177° 00.9' E, and is 1.5 km in diameter. The rate of bubble emission in the northern area is considerably less than that in the southern area, perhaps by a factor of 10.

Because of the extremely sporadic appearance of bubbles at any one point within the bubble areas, the gas forming the bubbles was not sampled. However, because the bubble areas are close to active geothermal areas on Whale Island, we think the bubbles are probably caused by submarine geothermal activity.

*Now at Institute of Geological Science, Ring Road Halton, Leeds.
N.Z. Jl mar. Freshwat. Res. 3: 602-6
Received for publication 15 May 1969

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