Magnetic observations made on la soufriere volcano (guadeloupe) during the 1976–1977 crisis

Abstract

An array of fourteen stations for measurement of the total intensity ( B) of the earth's magnetic field was installed on the Soufrière volcano during the 1976 seismovolcanic crisis. Measurements were performed daily from September 1976 to April 1977. Differences between values of the total intensity measured at each station and values of B measured continuously at a reference station (located near the summit of the volcano) have been computed. For each value of the difference, an estimate of an upper bound of the reduction error has been obtained. The effect of lateral conductivity anomalies has been directly measured for four stations and estimated for the others. The main conclusions of these experiments are the following: 1. (1) Significant variations are found in the differences in intensity with characteristic time constants of a few days. These variations are very small for stations located near the summit and within 5 km of the reference station; they reach an amplitude of 15 nT for the more remote stations and often show good correlation from station to station. 2. (2) The amplitude of these variations decreased with the end of the seismovolcanic crisis, at the end of March 1977.