Abstract
Particularly in the presence of a hydrothermal system, many volcanoes output large quantities of heat through the transport of water from deep within the edifice to the surface. Thus, heat flux is a prime tool for evaluating volcanic activity and unrest. We review the volcanic unrest at La Soufrière de Guadeloupe (French West Indies) using an airborne thermal camera survey and in situ measurements of temperature and flow rate through temperature probes, Pitot-tube and MultiGAS measurements. We deduce mass and heat fluxes for the fumarolic, ground and thermal spring outputs and follow these over a period spanning 2000–2020. Our results are compared with published data and we performed a retrospective analysis of the temporal variations in heat flux over this period using the literature data. We find that the heat emitted by the volcano is 36.5 ± 7.9MW, of which the fumarolic heat flux is dominant at 28.3 ± 6.8 MW. Given a total heated area of 26 270 m2, this equates to a total heat flux density of 1366 ± 82 W/m2, which is amongst the highest established for worldwide volcanoes with hydrothermal systems, particularly for dome volcanoes. A major change at La Soufrière de Guadeloupe, however, is the development of a widespread region of ground heating at the summit where heat output has increased from 0.2 ± 1 MW in 2010 to 5.7 ± 0.9 MW in 2020. This change is concurrent with accelerating unrest at the volcano and the emergence of two new high-flux fumaroles in recent years. Our findings highlight the importance of continued and enhanced surveillance and research strategies at La Soufrière de Guadeloupe, the results of which can be used to better understand hydrothermal volcanic systems the world over.
Highlights
Hydrothermal systems in active island-arc andesitic volcanoes are produced by the interaction of hot magmatic fluids, essentially gaseous water, CO2, H2 S and/or SO2 and HCl, produced by magma degassing at depth with marine or meteoric water at shallower depths and the host-rock (Sigurdsson et al 2015; Hedenquist and Lowenstern 1994)
As large fluxes can be observed by low intensity emissions over a large area, we calculate the total heat flux density, q = (Qrad + Qconv )/Aheated, as a metric for comparing intensity between sites
La Soufrière is an andesitic stratovolcano in the lesser Antilles arc with an extensive hydrothermal system that has undergone six phreatic/hydrothermal eruptions since 1635 C.E
Summary
Hydrothermal systems in active island-arc andesitic volcanoes are produced by the interaction of hot magmatic fluids, essentially gaseous water, CO2 , H2 S and/or SO2 and HCl, produced by magma degassing at depth with marine or meteoric water at shallower depths and the host-rock (Sigurdsson et al 2015; Hedenquist and Lowenstern 1994). The boiling of geothermal liquids liberates a fraction of the dissolved gases, which fractionate into the vapour phase that ascends to the surface through steam-dominated fumaroles. Partial condensation of these vapours into ground waters may generate steam-heated waters likely to disperse laterally where they can further mix with external waters and discharge as thermal springs (Hedenquist and Lowenstern 1994; Sigurdsson et al 2015).
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