A multi-decadal view of the heat and mass budget of a volcano in unrest: La Soufrière de Guadeloupe (French West Indies)

Abstract

Particularly in the presence of a hydrothermal system, volcanoes output great amounts of heat primarily 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 (temperature and flow rate). We deduce mass and heat fluxes for the fumarolic, ground and thermal spring outputs and follow these over a period spanning 20 years. We compare our results to published data to and perform a retrospective analysis of the temporal variations in heat flux over this period.We find that the heat emitted by the volcano is 36.5 ± 7.9 MW, of which the fumarolic heat flux is dominant at 28.3 ± 6.8 MW. Given a total heated area of 26 279 m 2 , this equates to a heat-flux density of 627 ± 94 W/m 2 , which value 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 ± 0.1 MW in 2010 to 5.7 ± 0.9 MW in the present study. This change is concurrent with accelerating unrest at the volcano, and the emergence of new high-flux fumaroles in recent years. Our findings highlight the need for continued and enhanced surveillance and research strategies at La Soufrière de Guadeloupe, the results of which can be used to better understand hydrothermal volcanism the world over.