A study of the geochemical evolution of Carbet l'Echelle spring, continued during 1981 and 1982 (figure 10). The water temperature decreased from 62.5°C in January 1981 to 50° in September 1982, while the concentration of HCO₃ ions continued to increase (+ 30%). Moreover, although large variations in Cl concentration have been observed since 1979, the background level of Cl began to fall in September 1981 and was reduced by half in one year. Likewise, the concentration of F ions, which has oscillated around a constant value since the beginning of the survey, decreased slightly in late 1982. Water temperatures and chemistry remained nearly constant at the other springs monitored by this study.

Figure 10. Changes in temperature (°C), HCO3 and Cl concentration (103 moles/liter), and F concentration (105 moles/liter) for Carbet l'Echelle spring, 500 m from the summit of Soufrière Guadeloupe, January 1981-September 1982.

Further References: Bigot, S., and Hammouya, G., 1987, Surveillance hydrogéochimique de la Soufrière de Guadeloupe, 1979-1985: Diminuition d'activité ou confinement?: C.R. Acad. Sci. Paris, t. 304, Série II, no. 13, p. 757-760.

Observations volcanologiques: Rapport d'Activité des Observatoires Volcanologiques des Antilles (Guadeloupe-Martinique) - November 1976-April 1977, April 1977-December 1978, 1979, 1980, 1981, 1982, and 1983-1984: Institut de Physique du Globe, Paris.

Geological Summary. La Soufrière de la Guadeloupe volcano occupies the southern end of Basse-Terre, the western half of the island of Guadeloupe. Construction of the Grand Découverte volcano about 200,000 years ago was followed a Plinian eruption and caldera formation about 100,000 years later, 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 3,100 years ago, respectively. The present 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. Six phreatic explosive eruptions since 1690 opened radial fractures across the summit lava dome. The phreatic eruptions in 1976-77 caused severe economic disruption when Basse-Terre, the island's capital city immediately below the volcano, was evacuated.

Information Contacts: S. Bigot, Lab. de Géochemie, Paris; G. Hammouya, Lab. de Physique du Globe; J. Le Mouel, J. Cheminée, IPG, Paris.