Low-Temperature Hydrothermal Systems Response to Rainfall Forcing: An Example From Temperature Time Series of Fumaroles at La Soufrière de Guadeloupe Volcano

Abstract

Volcanoes with highly-developed and shallow hydrothermal systems may be subject to sudden increases of their surface steam emission at vents in response to either deep forcing (e.g. increase of heat flux coming from the magma chamber) or external forcing (e.g. sudden decrease of atmospheric pressure or variation of meteoric water input). Because the vent plumbing has a limited heat and mass transfer capacity, the rise of steam pressure accompanying the increase of flux may destabilize the system in order to augment its net transfer capacity. This reorganization may, for instance, take the form of an enlargement of existing conduits and vents or to the creation of new ones. In such a case, local and extremely dangerous blast phenomena are likely to occur with devastating consequences several hundreds of meters around. Even volcanoes with a moderate activity and considered safe by the local population are exposed to such abrupt and dangerous events. The detection of early warning signals through temperature monitoring in the vents is of a primary importance and a main difficulty is to correctly interpret temperature jumps in order to reduce false alarms. We analyze time series of the temperature measured in three fumaroles located at the top of La Soufrière volcano in Guadeloupe, which are characterized by their relatively low temperature around 99°C, slightly above the boiling temperature of water at this altitude. Thanks to the long duration of the records from January to August 2017 and to their short 1-s sampling interval, a multiscale analysis can be performed over several orders of magnitude. We show that, despite their complex and sometimes erratic appearance, the temperature variations observed in the vents contain components highly correlated with rain input variations. Some remarkable patterns recurrently appear at different periods and we show that the main temperature variations of more than 10°C are related to the rainfall intensity. Our results illustrate the importance of external forcing on the otherwise complex and possibly chaotic dynamics of the shallow hydrothermal system of La Soufrière. They also reveal that a careful analysis of rainfall forcing must be done to be able to draw any conclusion concerning changes caused by the underlying hydrothermal system.

Environmental Stability and Its Importance for the Emergence of Darwinian Evolution

“…Time series from the siliceous hot spring of El Tatio, Chile [35] and from Fox Glacier, Uruni and Hanmer Springs, New Zealand [33] indicate daily variations on the order of 10 K, partly due to daily fluctuations in air temperature. Volcanic fumaroles from the La Soufriere volcano were found to have several orders of temperature variations, with daily variations of 1-2 K and monthly variations of 10 K [39].…”

Monitoring Hydrothermal Activity Using Major and Trace Elements in Low-Temperature Fumarolic Condensates: The Case of La Soufriere de Guadeloupe Volcano

“…After the 2018 volcanic unrest, CS fumaroles continued with fluctuating outlet gas temperatures (95 • C-111 • C [11,56]), variable chemistry of fumarolic gases [10,11], and visible morphological changes at the vent [57]. Temperature increases have been related to heat inputs in the roots of the hydrothermal system, while the temperature drops to the more significant input of meteoric waters and host-rock permeability changes [11,20]. Similarly, the chemistry of fumarolic gases displays variations during extended dry seasons, where an amplified magmatic signal of SO 2 arrives at the surface [10].…”

“…Depending on their size and the structural setting driving groundwater circulations, some hydrothermal systems may quickly react to external forcing factors. For example, it was recently reported that the significant input of meteoric waters due to heavy rainfalls into shallow hydrothermal systems can decrease the outlet gas temperatures of fumarolic emissions (e.g., [19,20]). Conversely, extended dry seasons seem to decrease scrubbing processes, amplifying the magmatic signal of discharged fluids (e.g., [10,21]).…”