New Zealand Journal of Geology and Geophysics abstracts

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Variation of magnetisation on White Island, New Zealand

D. J. WOODWARD
T. C. MUMME

Institute of Geological & Nuclear Sciences Ltd
P.O. Box 1320
Wellington, New Zealand

Abstract Measurements of the magnetisation of andesitic rocks from White Island have been combined with an interpretation of an aeromagnetic survey of the island to show the high variability of magnetisation in the rocks. Sampling of the rocks on White Island shows that, as expected, fresh andesitic lavas are highly magnetised (up to 20 A/m) whilst the phreatomagmatic deposits and altered andesites are weakly magnetised (<1 A/m). Most of the island is composed of layers of differing thicknesses of phreatomagmatic deposits and andesitic flows, so that the apparent magnetisations of the rocks, determined from the aeromagnetic survey, lie between 2.0 and 10.0 A/m. Highly magnetic rocks are concentrated in the floor of the crater exposed to the sea in the east of the island. These rocks, with a measured average magnetisation of >10 A/m, occur in three settings. They form a ring around the outside of the crater floor; there is a group of them between Shark Bay and Troup Head in the east of the island; and there are two areas of strong magnetisation associated with the active crater and a region c. 100 m due east of Donald Mound. The highly magnetised rocks within the crater are probably fresh andesitic flows and sills. Older andesite within the crater has probably been altered by the corrosive volcanic gases. On the northwestern coast of the island, magnetic anomalies indicate magnetisations >10 A/m that could be associated with rocks of the Western Cone.

Keywords White Island; volcano; magnetisation; terrain effects; aeromagnetic

Received 9 April 1992; published 3 December 1993
New Zealand Journal of Geology & Geophysics, 1991, Vol. 36: 447—451
0028Ð8306/06/3604—0447 ©The Royal Society of New Zealand 1991

PDF file of entire paper: medium quality (499K); (scanned from paper original: notes about this process). Digitisation of this article from the printed journal was kindly facilitated by the Geological Society of New Zealand

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