CO₂ favours the accumulation of excess fluids in felsic magmas

Abstract

Deformation and gas emissions at active volcanoes provide insights into volcanic plumbing systems. Large discrepancies are observed between the volumes calculated from deformation data and the volumes of erupted magmas and are ascribed to the amount of excess fluids in magma reservoirs, which hinders our capacity to predict the magnitude of an imminent eruption. Here, a series of experiments demonstrates that the amount of trapped excess fluids in felsic magmas depends strongly on fluid composition. Magmas with CO2 excess fluids become permeable at 44% larger porosities with respect to the H2O‐rich counterparts at equivalent crystallinity. Available excess gas geochemistry and juvenile porosity data from felsic systems reveal that the volume discrepancy between erupted magma and syn‐eruptive SO2 increases with CO2 excess in magmas. These data highlight that CO2‐rich fluids enhance magma's capacity to store excess volatiles and shed light on the largest discrepancies between pre‐eruptive deformation and eruption intensity and magnitude.

Redox behavior of degassing magmas: critical review and comparison of glass-based oxybarometers with application to Etna volcano

“…The distributions of MIs' dissolved volatile contents from many volcanic sites show in particular that maximum dissolved CO 2 contents measured in MIs cannot be reconciled with degassing patterns, demonstrating that a significant CO 2 -rich exsolved fluid phase exists at depth [e.g., Spilliaert et al, 2006, Aiuppa et al, 2007, 2010, Vigouroux et al, 2008, Allard, 2010, Blundy et al, 2010, Mormone et al, 2011, Oppenheimer et al, 2011, Pino et al, 2011, Moretti et al, 2013a,b, 2018, Caricchi et al, 2018, Paonita et al, 2021. This evidences that CO 2 dissolved in deep melts significantly underestimates the total CO 2 content, which is in line with the clear imbalance between magma production (magma emitted at the surface and piled up in volcanic edifices) and degassing rates at many volcanic sites, which in turn implies deep degassing sources [e.g., Aiuppa et al, 2007, 2013, Shinohara, 2008, Moretti et al, 2013a,b, Paonita et al, 2021, Pistone et al, 2021, Utami et al, 2021.…”

Dynamics between earthquakes, volcanic eruptions, and geothermal energy exploitation in Japan

“…Laboratory experiments demonstrate that magma with entrapped fluids ( O and ) are of 0.1–10 wt% and there porosity is greater than about 60 vol% 79 , 80 . Consequently, a porosity of 0.6 for the magmatic fluid is assumed and a porosity of 0.03 is assumed for the rock matrix 81 .…”

Reckoning with the Rocky Relationship Between Eruption Size and Climate Response: Toward a Volcano-Climate Index

“…In parallel with the excess sulfur problem, excess carbon is likely a near-universal feature of volcanic activity because CO 2 saturation can occur relatively deep in the crust owing to strong decreases in CO 2 solubility with decreasing pressure, enabling decoupling and transfer of CO 2 from magmas that do not erupt. Indeed, high CO 2 concentrations can drive melt volatile saturation and development of a coexisting fluid into which sulfur also partitions (Pistone et al 2021), implying potential coupling of excess volatiles. The question of excess carbon has received less attention than that of excess sulfur because CO 2 is challenging to detect by satellite (Burton et al 2013), much of the exsolved CO 2 may be released via diffuse degassing during quiescent intervals (Werner et al 2019), and CO 2 from individual explosive eruptions carries negligible climate consequences.…”