Case study of a volcanic geothermal system, Mount Pelée, Martinique

Abstract

Listen

Translate article

Mount Pelée is one of the active volcanoes of the Lesser Antilles arc, with more than 20 eruptions during the last 5000 years. Despite this abundant potential heat flow, there are few surface manifestations indicative of the existence of a large high-temperature hydrothermal system. A few Na-HCO 3 -SO 4 -type hot springs with emergence temperatures not exceeding 65°C occur on the south and west flanks of the volcano. Two small hydrothermal eruptions occurred in 1792 and 1851 on the southwestern flank, on the site of now-extinct sulfur springs. The heat source provided by the Mount Pelée magma chamber should occur, according to petrologic data, at shallow depth (5–8 km) beneath the summit region. We assume abundant groundwater recharge to take place within the central calderas where faults and magmatic conduits provide vertical channelways for deep infiltration of cold meteoric water. This would be expected to depress a presumed NaCl hydrothermal system located deep in the core of the volcano. Upwelling of high-temperature fluids and gases is thought to be found at the periphery of the central calderas, along the arcuate caldera-related faults and/or along regional faults and any permeable stratigraphic levels connected to the central caldera structure. Steam heating of shallow meteoric waters by a degassing NaCl system could produce a Na-HCO 3 -SO 4 -type system, which would develop preferentially on the periphery of the central caldera structure or even outside it in an adjacent zone of fracture permeability (caldera or regional faults), where cold meteoric flows are less abundant. This Na-HCO 3 -SO 4 system is assumed to be located beneath the south flank of the volcano, and the major upflow zone seems to be the southern limit of the intermediate caldera, as evidenced by the location of hot springs and hydrothermal eruptions. The scarcity of thermal manifestations on Mount Pelée is not surprising in view of its groundwater hydrogeology. The Na-HCO 3 -SO 4 fluids which ascend will be masked wherever a highly permeable, subhorizontal aquifer occurs near the surface, and they commonly mix with cold waters before discharging.