Magnetic observations on La Soufriere volcano (Guadeloupe; F.W.I.) over a quiet period; Background estimation.

Abstract

Since 1978 the routine surveillance of La Soufrière volcano (Guadeloupe, F.W.I.) is performed using measurements of the total intensity (B) of the Earth magnetic field made at 3 stations radio-transmitted to the Fort Saint-Charles observatory. Differences ΔB between values of B measured at two of these stations and the one simultaneously measured at the third one (Matouba, the reference station) are computed; values of ΔB recorded around 2:00a.m. are used to monitor the volcano-magnetic field. These 3 stations are installed in areas where (1) the reduction and projection errors are as weak as possible (2) the volcano-magnetic signal is expected to be noticeable during a volcanic crisis. The observations made using this network during the years 1979 to 1981 are presented. During these 3 years of no abnormal volcanic activity, the volcano-magnetic field, if any, remains below the experimental noise level.