Report on Soufriere Guadeloupe (France) — April 1976
Natural Science Event Bulletin, vol. 1, no. 7 (April 1976)
Managing Editor: David Squires.
Soufriere Guadeloupe (France) Seismic crisis during November 1975-April 1976; no surface activity
Please cite this report as:
Global Volcanism Program, 1976. Report on Soufriere Guadeloupe (France). In: Squires, D (ed.), Natural Science Event Bulletin, 1:7. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.NSEB197604-360060.
16.044°N, 61.664°W; summit elev. 1467 m
All times are local (unless otherwise noted)
The recent seismic crisis began in November 1975 when 25 tremors were recorded. Thirty tremors were registered in December, 36 in January 1976, 93 in February, and 680 in March (of which 1/3 were felt by inhabitants very near the volcano). The crisis was declining at the end of April. The foci of the tremors were under the NW part of Soufrière, and depths of focus varied from 1 to 5 km.
No new surface manifestations accompanied or followed these tremors (up to 9 April). There were no modifications of temperatures nor of the composition of gases emitted by the fumaroles. An overflight of the volcano did not indicate any sign of abnormal activity on the surface. . . .
Local earthquake swarms are rather frequent at volcanoes of this type. They have taken place approximately once per year on Guadeloupe since 1962, but none have reached the frequency of March 1976. The same phenomenon has previously occurred on neighboring islands (Montserrat 1966, St. Kitts in 1950 and 1961, and St. Vincent 1947) without any eruption.
J. Dorel believes that, for the present time, there is no important risk of an eruption of this volcano, but that it is impossible to make a long-term (several months or years) prognostication on the evolution of such volcanoes.
Geologic Background. La Soufrière de la Guadeloupe volcano occupies the southern end of Basse-Terre, the western half of the butterfly-shaped island of Guadeloupe. Construction of the Grand Découverte volcano about 0.2 million years ago (Ma) was followed by caldera formation after a plinian eruption about 0.1 Ma, and then by construction of the Carmichaël volcano within the caldera. Two episodes of edifice collapse and associated large debris avalanches formed the Carmichaël and Amic craters about 11,500 and 3100 years ago, respectively. The presently active La Soufrière volcano subsequently grew within the Amic crater. The summit consists of a flat-topped lava dome, and several other domes occur on the southern flanks. Most historical eruptions have originated from NW-SE-trending fissure systems that cut across the summit and upper flanks. A relatively minor phreatic eruption in 1976-77 caused severe economic disruption when Basse-Terre, the island's capital city, which lies immediately below the volcano, was evacuated.
Information Contacts: J. Dorel, IPG, Paris.