SURVEILLANCE OF WHITE ISLAND VOLCANO, 1968–1972

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Abstract
Total field magnetic surveys were carried out over the crater floor of White Island on seven occasions between May 1968 and August 1971. Changes in magnetic field near Rudolf vent, which began erupting ash in February 1968, were related to its subsequent decrease in activity. Changes in magnetic field also preceded the eruption of 1971 Crater in July 1971. These became apparent in the survey of April 1971, four months before the eruption. We assume that an increase in temperature at depth precedes and leads up to the eruption. If the temperature variations of andesitic rock are largely responsible for the variations in magnetisation, the observed magnetic and level changes can be accounted for by postulating a temperature change within a specific region. A temperature change of 50°c within a spherical volume 125 m in radius centred at a depth of 200 m would account for both the measured magnetic and level variations. In volcanic centres like White Island, monitoring of both magnetic field and ground levels, taken in conjunction, shows promise for predicting eruptions.

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