Highly explosive basaltic eruptions driven by CO2 exsolution

Abstract

The most explosive basaltic scoria cone eruption yet documented (>20 km high plumes) occurred at Sunset Crater (Arizona) ca. 1085 AD by undetermined eruptive mechanisms. We present melt inclusion analysis, including bubble contents by Raman spectroscopy, yielding high total CO2 (approaching 6000 ppm) and S (~2000 ppm) with moderate H2O (~1.25 wt%). Two groups of melt inclusions are evident, classified by bubble vol%. Modeling of post-entrapment modification indicates that the group with larger bubbles formed as a result of heterogeneous entrapment of melt and exsolved CO2 and provides evidence for an exsolved CO2 phase at magma storage depths of ~15 km. We argue that this exsolved CO2 phase played a critical role in driving this explosive eruption, possibly analogous to H2O exsolution driving silicic caldera-forming eruptions. Because of their distinct gas compositions relative to silicic magmas (high S and CO2), even modest volume explosive basaltic eruptions could impact the atmosphere.

VESIcal Part II: A critical approach to volatile solubility modelling using an open-source Python3 engine

“…As equation 4 includes a term for the fugacity of H 2 O in the fluid, this model can be integrated with CO 2 models implemented in VESIcal (e.g., the Π-SiO 2 simplification of , Liu et al, 2005, Iacono-Marziano et al, 2012, Shishkina et al, 2014, Allison et al, 2019 to investigate mixed…”

“…This lack of intercomparison likely results from the fact that it is extremely time consuming to perform the large numbers of calculations necessary for thorough comparisons using available tools. For example, many solubility models were released as stand-alone Excel spreadsheets (e.g., G. Newman & Lowenstern, 2002;Allison et al, 2019) or web apps (e.g., Iacono-Marziano et al, 2012;, where saturation pressures, dissolved volatile contents, degassing paths, and isobars can only be calculated for one sample and set of conditions at a time. The more recent models which include several terms accounting for the effect of melt composition on volatile solubility require users to hand-type a large number of input parameters.…”

“…It has become increasingly apparent from solubility experiments that while the solubility of H 2 O is relatively insensitive to melt composition (e.g., G. Shishkina et al, 2010), CO 2 solubility is highly sensitive to melt composition, particularly in mafic melts where the carbonate ion is the dominant species Brooker et al, 2001a;Shishkina et al, 2010;Iacono-Marziano et al, 2012;Shishkina et al, 2014;Allison et al, 2019). This has lead to a great diversity in the way that various models treat the dependence of CO 2 solubility on melt composition.…”

“…In general, models have become more complex with time as the region of compositional space spanned by solubility experiments has increased to include more alkaline lavas. The individual role and relative importance of each cation species in the melt is still associated with a large degree of uncertainty (Allison et al, 2019), accounting for the larger discrepancies between different model predictions for…”

Volcanically extruded phosphides as an abiotic source of Venusian phosphine

“…Some basaltic eruptions are now recognized as extremely violent, i.e., generating widespread phreatomagmatic, sub-Plinian and Plinian fall deposits (i.e., the eruption of Tarawera 1886) ( 60 ). In those cases, the explosive behavior depends on many other factors other than high viscosity, i.e., the decompression history, the contribution of other volatiles such as CO 2 , SO 2 besides water ( 61 ), and conduit processes such as the development of largely stagnant and outgassed melt restricting the effective radius of the conduit ( 60 ).…”