Sulfur is the tenth most abundant element in the Universe, and a widely distributed element on Earth. Due to its variable valence states, it participates in a variety of geo- and biochemical processes. Elemental sulfur (Se) occurs in evaporite formations and in volcanic settings as well as in products of petroleum refining. Due to its complex polymerization behavior, elemental S viscosity is highly temperature dependent: from low viscosity around its variable melting point (94-133°C), a 10,000-fold increase occurs at ~160?C, until a maximum between 186-188oC. Nevertheless, this pattern differs when impurities (organics, H2S(x), ammonia, halogens) are present. Many phreatic and phreatomagmatic eruptions were attributed to a system sealing at depth, arguably caused by this sharp increase in viscosity, especially at crater lake-hosting volcanoes. In magmas, sulfur has a complex behavior dissolving both as sulfide (S2-), and sulfate (S6+), and sulfur gases from magmas (SO2 or H2S) differ depending on oxygen abundance (fO2), temperature, pressure and melt composition. Moreover, S-aerosols derived from SO2 injected into the atmosphere by eruptive plumes cause climate disruption by cooling the Earth’s surface (0.13- 1.3 ºC), as it has been proven by several eruptions during the past centuries.
Volcanic sulfur is the most impure sulfur source in nature, but this aspect remains poorly investigated and partially acknowledged in volcanology despite the ubiquitous occurrence of this element in volcano-hydrothermal settings. Detecting precursory signals of volcanic unrest is critical in volcano monitoring; geochemical monitoring plays a fundamental role in predicting the onset of volcanic unrest and possibly eruptions. Yet, sulfur concentrations in melts, the source of subsequent anomalies manifested at the surface, are poorly constrained. S-rich mineral layers accumulated at depth are the evidence that some signals detected at the surface (springs, lakes) or in the atmosphere (volcanic plumes) may be contrasting due to S sequestration or scrubbing. In the ultimate case variations in S-viscosity could seal the volcanic system, leading to its overpressurization, and ultimately its unheralded failure, stating the active role of S dynamics as a potential cause of eruptions.
We welcome all studies that can improve our knowledge on the properties of sulfur in any state, as a solid, solute or gas phase, in volcanic and hydrothermal settings. Quantitative results, in situ sampling, mapping, continuous direct monitoring, remote sensing analyses – either ground based (e.g. DOAS-FTIR) or from satellite, data resulting from interdisciplinary work (i.e. mixed geochemical/ geophysical monitoring) are welcome in this Research Topic. Moreover, experimental studies on S-solubility in melts and S-viscosity measurements at different conditions of pressure (mostly low) and temperatures (typical for hydrothermal systems) could provide groundbreaking steps ahead on the state of knowledge of the role of S in volcanic systems.
Sulfur is the tenth most abundant element in the Universe, and a widely distributed element on Earth. Due to its variable valence states, it participates in a variety of geo- and biochemical processes. Elemental sulfur (Se) occurs in evaporite formations and in volcanic settings as well as in products of petroleum refining. Due to its complex polymerization behavior, elemental S viscosity is highly temperature dependent: from low viscosity around its variable melting point (94-133°C), a 10,000-fold increase occurs at ~160?C, until a maximum between 186-188oC. Nevertheless, this pattern differs when impurities (organics, H2S(x), ammonia, halogens) are present. Many phreatic and phreatomagmatic eruptions were attributed to a system sealing at depth, arguably caused by this sharp increase in viscosity, especially at crater lake-hosting volcanoes. In magmas, sulfur has a complex behavior dissolving both as sulfide (S2-), and sulfate (S6+), and sulfur gases from magmas (SO2 or H2S) differ depending on oxygen abundance (fO2), temperature, pressure and melt composition. Moreover, S-aerosols derived from SO2 injected into the atmosphere by eruptive plumes cause climate disruption by cooling the Earth’s surface (0.13- 1.3 ºC), as it has been proven by several eruptions during the past centuries.
Volcanic sulfur is the most impure sulfur source in nature, but this aspect remains poorly investigated and partially acknowledged in volcanology despite the ubiquitous occurrence of this element in volcano-hydrothermal settings. Detecting precursory signals of volcanic unrest is critical in volcano monitoring; geochemical monitoring plays a fundamental role in predicting the onset of volcanic unrest and possibly eruptions. Yet, sulfur concentrations in melts, the source of subsequent anomalies manifested at the surface, are poorly constrained. S-rich mineral layers accumulated at depth are the evidence that some signals detected at the surface (springs, lakes) or in the atmosphere (volcanic plumes) may be contrasting due to S sequestration or scrubbing. In the ultimate case variations in S-viscosity could seal the volcanic system, leading to its overpressurization, and ultimately its unheralded failure, stating the active role of S dynamics as a potential cause of eruptions.
We welcome all studies that can improve our knowledge on the properties of sulfur in any state, as a solid, solute or gas phase, in volcanic and hydrothermal settings. Quantitative results, in situ sampling, mapping, continuous direct monitoring, remote sensing analyses – either ground based (e.g. DOAS-FTIR) or from satellite, data resulting from interdisciplinary work (i.e. mixed geochemical/ geophysical monitoring) are welcome in this Research Topic. Moreover, experimental studies on S-solubility in melts and S-viscosity measurements at different conditions of pressure (mostly low) and temperatures (typical for hydrothermal systems) could provide groundbreaking steps ahead on the state of knowledge of the role of S in volcanic systems.