Understanding Degassing Pathways Along the 1886 Tarawera (New Zealand) Volcanic Fissure by Combining Soil and Lake CO2 Fluxes

Abstract

CO 2 flux measurements are often used to monitor volcanic systems, understand the cause of volcanic unrest, and map sub-surface structures. Currently, such measurements are incomplete at Tarawera (New Zealand), which erupted with little warning in 1886 and produced a ∼17 km long fissure. We combine new soil CO 2 flux and C isotope measurements of Tarawera with previous data from Rotomahana and Waimangu (regions also along the 1886 fissure) to fingerprint the CO 2 source, understand the current pathways for degassing, quantify the CO 2 released along the entire fissure, and provide a baseline survey. The total CO 2 emissions from the fissure are 1227 t•d −1 (742-3398 t•d −1 90 % confidence interval), similar to other regions in the Taupō Volcanic Zone. The CO 2 flux from Waimangu and Rotomahana is far higher than from Tarawera (>549 vs. ∼4 t•d −1 CO 2), likely influenced by a shallow silicic body at depth and Okataina caldera rim faults increasing permeability at the southern end of the fissure. Highly localized regions of elevated CO 2 flux occur along the fissure and are likely caused by cross-cutting faults that focus the flow. One of these areas occurs on Tarawera, which is emitting ∼1 t•d −1 CO 2 with a δ 13 CO 2 of −5.5 ± 0.5 , and comparison with previous observations shows that activity is declining over time. This region highlights the spatial and temporal complexity of degassing pathways at volcanoes and that sub-surface structures exert a primary control on the magnitude of CO 2 flux in comparison to the surface mechanism (i.e., CO 2 released through the soil or lake surface).

Storage, evolution, and mixing in basaltic eruptions from around the Okataina Volcanic Centre, Taupō Volcanic Zone, Aotearoa New Zealand

“…The measured water contents overlap with inferred melt water contents from melt inclusions and clinopyroxene H contents from Rowe et al (2021). A CO2 content of 800 ppm would require at least 0.9 to 4.3 × 10 6 t/d (90 % confidence interval) of magma to degas fully to sustain the current levels of passive CO2 emissions observed along the Tarawera fissure (Hughes et al, 2019b;Mazot et al, 2014). Positive correlation of Al2O3 and SiO2 in clinopyroxene-hosted melt inclusions, reaching up to ~22 wt% Al2O3, requires plagioclase-suppression during crystallisation, such that clinopyroxene (± olivine) crystallisation controls melt composition (Figure 4).…”

“…Some rhyolitic eruptions were preceded by basaltic eruptions, with either no (e.g., Matahi prior to Rotoiti) or direct (e.g., mixed basaltic-rhyolitic clasts in Okareka) evidence for magma mixing prior to eruption, whereas others (e.g., Rerewhakaaitu and Kaharoa) host basaltic blebs and enclaves (e.g., Burt et al, 1998;Cole, 1973a;Cole et al, 2014;Leonard et al, 2002;Nairn, 1992;Pullar and Nairn, 1972;Schmitz and Smith, 2004;Shane et al, 2007Shane et al, , 2008a. The OVC is passively degassing CO2 and heat today and inferred basaltic dike events also occur (e.g., Benson et al, 2021;Hughes et al, 2019b;Mazot et al, 2014). (n.d.), but are likely very small due to their limited occurrence (Nairn, 2002).…”

“…The volcanic infill depth is taken from Seebeck et al (2010) and the crust-mantle boundary from Bannister et al (2004). The caldera topographic edge is indicated with a vertical arrow pointing down (Nairn, 2002) and faults are indicated with dotted black lines (and sometimes labelledthere locations are taken from Seebeck et al (2010) and inferred from regions of high-CO2 emissions from Hughes et al (2019b)). Magmatic bodies are shown outlined in black, where the colour indicates the magma type: pink is Basalt-1, dark red is Basalt-2, yellow is Dacite-Rm, and orange is Rhyolite: their depths are based on this study and various other studies (Bannister et al, 2004;Cole et al, 2014;Heise et al, 2016Heise et al, , 2010Johnson et al, 2011;Sable et al, 2009).…”

CALDERA: a scientific drilling concept to unravel Connections Among Life, geo-Dynamics and Eruptions in a Rifting Arc caldera, Okataina Volcanic Centre, Aotearoa New Zealand

“…The heat from several hydrothermal systems outflowing on the edges of the caldera is inferred to come from the deep magmatic complex in the centre of the caldera . Magmatic fluids interact with abundant freshwater, including groundwater, rivers, lakes, and rainfall of 1.5-2 m yr −1 (Giggenbach, 1995;Mazot et al, 2014;Simpson and Bignall, 2016;Hughes et al, 2019;Pearson-Grant et al, 2022;Yang et al, 2023). Diverse microbiota have been identified in the caldera and rift-straddling Waimangu geothermal field (Power et al, 2018(Power et al, , 2024.…”