Evidence for deep gas loss in open volcanic systems

Collombet, Marielle; Burgisser, Alain; Colombier, Mathieu und Gaunt, Elizabeth (2021): Evidence for deep gas loss in open volcanic systems. In: Bulletin of Volcanology, Bd. 83, Nr. 2, 7

Abstract

Previous studies of Vulcanian eruptive products have shown that the respective volcanic conduits were filled for the most part with low-porosity magma (i.e., < 10 vol%) prior to eruption. Comparison with the theoretical porosity distribution expected from closed-system degassing suggests that gas loss must have taken place at depth within the magmatic column (between 3 and 5 km). At such high pressures (between 70 and 110 MPa), however, porosities are low enough (< 20 vol%) to rule out traditional gas loss mechanisms. We tested if channelling, an outgassing mechanism based on bubble connection due to high crystal content (>40 vol%) proposed to occur in mushy magma reservoirs, could also happen in volcanic conduits. We reanalyzed phenocryst, microlite, and porosity data from recent eruptions of Merapi volcano, Indonesia, Soufriere Hills volcano, Montserrat, and Tungurahua volcano, Ecuador. Overall, these magmas had crystal contents high enough for outgassing to occur by channelling. Gases could be channelled out of the magma columns at various levels during ascent to yield mostly gas-depleted magma columns prior to explosive behavior. Such outgassing by channelling thus has the capacity to influence eruptive style. Depending on the phenocryst content, microlite growth during ascent can either foster or impede gas escape by channelling. Considering the pervasive occurrence of microlites and ensuing high crystal contents in volcanic conduits (between 40 and 70 vol%), the high likelihood of channelling implies that other outgassing mechanisms might not be as dominant as previously envisioned.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Geowissenschaften > Department für Geo- und Umweltwissenschaften
• Themengebiete: 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie
• ISSN: 0258-8900
• Sprache: Englisch