Abstract
The 1886 eruption of Tarawera, New Zealand, produced a ~17 km long fissure across the Tarawera Volcanic Complex (TVC), Lake Rotomahana (LR), and the Waimangu Geothermal System (WGS). We combine new soil CO2 flux and isotope measurements of TVC with previous data from LR and WGS to fingerprint the CO2 source, understand the current pathways for degassing, and quantify the CO2 released along the entire fissure. The total CO2 emissions from the fissure are 1227 t·d-1 (742–3398 t·d-1). The CO2 flux from WGS and LR is far higher than from TVC (>549 vs. ~4 t·d-1 CO2), likely influenced by a shallow silicic body at depth and caldera rim faults increasing permeability at the southern end of the fissure. Highly localised regions of high CO2 flux occur along the fissure and are likely caused by cross-cutting faults that focus the flow. One of these areas occurs in the TVC, which is emitting ~1 t·d-1 CO2 with a δ13CO2 of -5.5 ± 0.5 ‰, and comparison with previous observations shows that activity is declining over time. Future CO2 flux surveys could be compared to this baseline survey to understand changes in volcanic activity.
Highlights
Carbon dioxide (CO2) is the second most abundant gas emitted from magma and, due to its low solubility, exsolves at relatively high pressures (e.g., Mysen et al, 1975; Blank and Brooker, 1994; Ni and Keppler, 2013; Edmonds and Wallace, 2017)
Previous work has shown that the Waimangu-Rotomahana portion of the fissure has high CO2 emissions (Hurst et al, 2006; Mazot et al, 2014), but there was no quantification for the Tarawera portion of the fissure
We present new soil CO2 flux and isotope measurements collected on Tarawera, along the fissure created by the 1886 eruption
Summary
Carbon dioxide (CO2) is the second most abundant gas emitted from magma and, due to its low solubility, exsolves at relatively high pressures (mid-crust to potentially upper mantle) (e.g., Mysen et al, 1975; Blank and Brooker, 1994; Ni and Keppler, 2013; Edmonds and Wallace, 2017). We present new soil CO2 flux and isotope measurements collected on Tarawera, along the fissure created by the 1886 eruption These data are combined with measurements of soil CO2 flux at Waimangu (Hurst et al, 2006) and the surface CO2 flux of Lake Rotomahana (Mazot et al, 2014). We use these data to understand the source of CO2, investigate the controls on degassing pathways along the 1886 fissure, and calculate the total CO2 emissions. Our baseline survey can be compared to future measurements, especially during times of volcanic unrest
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