Backward tracking of gas chemistry measurements at Erebus volcano

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 13; no. 11; pp. np - n/a
• Main Authors: Burgisser, Alain, Oppenheimer, Clive, Alletti, Marina, Kyle, Philip R., Scaillet, Bruno, Carroll, Michael R.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01.11.2012; John Wiley & Sons, Inc; AGU and the Geochemical Society
• Subjects: Bars; Degassing; Earth Sciences; Environmental Sciences; Erebus volcano; eruptive mechanisms; Explosions; Global Changes; Lakes; Lava; Melts; Sciences of the Universe; Separation; Signatures; Slugs; thermodynamics; volcanic gas; Volcanoes; Volcanology; Antarctica; thermodynamics; eruptive mechanisms; Erebus volcano; volcanic gas
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2012GC004243

Erebus volcano in Antarctica offers an exceptional opportunity to probe the dynamics of degassing – its behavior is characterized by an active lava lake through which sporadic Strombolian eruptions occur. Here, we develop a framework for interpreting contrasting degassing signatures measured at high temporal resolution, which integrates physical scenarios of gas/melt separation into a thermodynamic model that includes new volatile solubility data for Erebus phonolite. In this widely applicable framework, the measured gas compositions are backtracked from surface to depth according to physical templates involving various degrees of separation of gas and melt during ascent. Overall, explosive signatures can be explained by large bubbles (gas slugs) rising slowly in equilibrium from at least 20 bars but at most a few hundred bars in a magmatic column closer to the stagnant end‐member than the convecting end‐member. The span of explosive signatures can be due to various departure depths and/or slug acceleration below a few tens of bars. Results also reveal that explosive gases last equilibrated at temperatures up to 300°C colder than the lake due to rapid gas expansion just prior to bursting. This picture (individual rise of gas and melt batches from a single, potentially very shallow phonolitic source) offers an alternative to the conclusions of previous work based on a similar data set at Erebus, according to which differences between quiescent and explosive gas signatures are due to the decompression of two deep, volatile‐saturated sources that mixed to various degrees (phonolite at 1–3 kbar and basanite at 5–8 kbar). Key Points We develop a framework to interpret gas signatures at active volcanoes Explosions at Erebus can be due to a single shallow phonolitic source Rapid expansion during bursting causes cooling that affects gas chemistry