J. M. de Moor

A new sulfur and carbon degassing inventory for the Southern Central American Volcanic Arc: The importance of accurate time-series datasets and possible tectonic processes responsible for temporal variations in arc-scale volatile emissions

This work presents a new database of SO2 and CO2 fluxes from the Southern Central American Volcanic Arc (SCAVA) for the period 2015-2016. We present ∼300 SO2 flux measurements from 10 volcanoes and gas ratios from 11 volcanoes in Costa Rica and Nicaragua representing the most extensive available assessment of this ∼500 km arc segment. The SO2 flux from SCAVA is estimated at 6,240±1,150 T/d, about a factor of three higher than previous estimations (1972-2013). We attribute this increase in part to our more complete assessment of the arc. Another consideration in interpreting the difference is the context of increased volcanic activity, as there were more eruptions in 2015-2016 than in any period since ∼1980. A potential explanation for increased degassing and volcanic activity is a change in crustal stress regime (from compression to extension, opening volcanic conduits) following two large (Mw>7) earthquakes in the region in 2012. The CO2 flux from the arc is estimated at 22,500±4,900 T/d, which is equal to or greater than estimates of C input into the SCAVA subduction zone. Time-series datasets for arc degassing need to be improved in temporal and spatial coverage to robustly constrain volatile budgets and tectonic controls. Arc volatile budgets are strongly influenced by short-lived degassing events and arc systems likely display significant short-term variations in volatile output, calling for expansion of nascent geochemical monitoring networks to achieve spatial and temporal coverage similar to traditional geophysical networks.

Carbon isotope systematics of Turrialba volcano, Costa Rica, using a portable cavity ring‐down spectrometer

Over the past two decades, activity at Turrialba volcano, Costa Rica, has shifted from hydrothermal to increasingly magmatic in character, with enhanced degassing and eruption potential. We have conducted a survey of the δ13C signatures of gases at Turrialba using a portable field-based CRDS with comparison to standard IRMS techniques. Our δ13C results of the volcanic plume, high temperature vents and soil gases reveal isotopic heterogeneity in the CO2 gas composition at Turrialba prior to its recent phase of eruptive activity. The isotopic value of the regional fault system, Falla Ariete (-3.4±0.1‰), is in distinct contrast with the Central crater gases (-3.9±0.1‰) and the 2012 high temperature vent (-4.4±0.2‰), an indication that spatial variability in δ13C may be linked to hydrothermal transport of volcanic gases, heterogeneities in the source composition, or magmatic degassing. Isotopic values of CO2 samples collected in the plume vary from δ13C of -5.2 to -10.0 ‰, indicative of mixing between atmospheric CO2 (-9.2 ± 0.1‰), and a volcanic source. We compare the Keeling method to a traditional mixing model (hyperbolic mixing curve) to estimate the volcanic source composition at Turrialba from the plume measurements. The predicted source compositions from the Keeling and hyperbolic methods (-3.0±0.5‰ and -3.9±0.4‰, respectively) illustrate two potential interpretations of the volcanic source at Turrialba. As of the 29 October 2014, Turrialba has entered a new eruptive period, and continued monitoring of the summit gases for δ13C should be conducted to better understand the dominant processes controlling δ13C fractionation at Turrialba.