J. Maarten de Moor

Turmoil at Turrialba Volcano (Costa Rica): Degassing and eruptive processes inferred from high-frequency gas monitoring

Abstract Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high‐frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO2‐rich gas (CO2/Stotal > 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are accompanied by shallowly derived sulfur‐rich magmatic gas emissions. Degassing modeling suggests that the deep magmatic reservoir is ~8–10 km deep, whereas the shallow magmatic gas source is at ~3–5 km. Two cycles of degassing and eruption are observed, each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels. The magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system, modifying the gas compositions, contributing volatiles to the emissions, and reflecting complex processes of scrubbing, displacement, and volatilization. H2S/SO2 varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases, whereas the second did not. Massive degassing (>3000 T/d SO2 and H2S/SO2 > 1) followed, suggesting boiling off of the hydrothermal system. The gas emissions show a remarkable shift to purely magmatic composition (H2S/SO2 < 0.05) during the second eruptive period, reflecting the depletion of the hydrothermal system or the establishment of high‐temperature conduits bypassing remnant hydrothermal reservoirs, and the transition from phreatic to phreatomagmatic eruptive activity.

Eruptive activity at Turrialba volcano (Costa Rica): Inferences from 3He/4He in fumarole gases and chemistry of the products ejected during 2014 and 2015

A new period of eruptive activity started at Turrialba volcano, Costa Rica, in 2010 after almost 150 years of quiescence. This activity has been characterized by sporadic explosions whose frequency clearly increased since October 2014. This study aimed to identify the mechanisms that triggered the resumption of this eruptive activity and characterize the evolution of the phenomena over the past 2 years. We integrate 3He/4He data available on fumarole gases collected in the summit area of Turrialba between 1999 and 2011 with new measurements made on samples collected between September 2014 and February 2016. The results of a petrological investigation of the products that erupted between October 2014 and May 2015 are also presented. We infer that the resumption of eruptive activity in 2010 was triggered by a replenishment of the plumbing system of Turrialba by a new batch of magma. This is supported by the increase in 3He/4He values observed since 2005 at the crater fumaroles and by comparable high values in September 2014, just before the onset of the new eruptive phase. The presence of a number of fresh and juvenile glassy shards in the erupted products increased between October 2014 and May 2015, suggesting the involvement of new magma with a composition similar to that erupted in 1864–1866. We conclude that the increase in 3He/4He at the summit fumaroles since October 2015 represents strong evidence of a new phase of magma replenishment, which implies that the level of activity remains high at the volcano. This article is protected by copyright. All rights reserved.

Tracking Formation of a Lava Lake From Ground and Space: Masaya Volcano (Nicaragua), 2014–2017

A vigorously degassing lava lake appeared inside the Santiago pit crater of Masaya volcano (Nicaragua) in December 2015, after years of degassing with no (or minor) incandescence. Here, we present an unprecedented-long (3 years) and continuous volcanic gas record that instrumentally characterizes the (re)activation of the lava-lake. Our results show that, before appearance of the lake, the volcanic gas plume composition became unusually CO2-rich, as testified by high CO2/SO2 ratios (mean, 12.2±6.3) and low H2O/CO2 ratios (mean, 2.3±1.3). The volcanic CO2 flux also peaked in November 2015 (mean, 81.3±40.6 kg/s; maximum, 247 kg/s). Using results of magma degassing models and budgets, we interpret this elevated CO2 degassing as sourced by degassing of a volatile-rich fast-convecting (3.6-5.2 m3·s-1) magma, supplying CO2-rich gas bubbles from minimum equivalent depths of 0.36-1.4 km. We propose this elevated gas bubbles supply destabilized the shallow (<1 km) Masaya magma reservoir, leading to upward migration of vesicular (buoyant) resident magma, and ultimately to (re)formation of the lava lake. At onset of lava lake activity on 11 December 2015 (constrained by satellite-based (MODIS) thermal observations), the gas emissions transitioned to more SO2-rich composition, and the SO2 flux increased by a factor ~40 % (11.4±5.2 kg/s) relative to background degassing (8.0 kg/s), confirming faster than normal (4.4 vs. ~3 m3·s-1) shallow magma convection. Elevated shallow magma circulation is also supported by gradual increase in irradiated thermal energy, captured by MODIS, from which we calculate that 0.4-0.8 m3·s-1 of magma have been surface-emplaced since December 2015.

Relationship between Diffuse CO2 Degassing and Volcanic Activity. Case Study of the Poás, Irazú, and Turrialba Volcanoes, Costa Rica

Active volcanoes exhibit diffuse gas emanations through the ground, the most abundant species of which is CO2. However, the relationship between diffuse degassing and volcanic activity is not often clear and some volcanoes may have low diffuse degassing levels despite having strong volcanic activity. The main goals of this study are to quantify diffuse CO2 degassing and determine whether patterns exist in relation to volcanic activity through the study of Turrialba, Poas and Irazu, three active volcanoes in Costa Rica which are at different stages of activity. Structural controls of spatial distribution of diffuse degassing were also investigated. Measurement campaigns were conducted using the accumulation chamber method coupled with 10 cm depth ground temperature sampling with the aim of estimating the total diffuse CO2 degassing budget. The total amount of CO2 emitted diffusely by each volcano is approximately 113 ± 46 t/d over ~ 0.705 km2 for Turrialba, 0.9 ± 0.5 t/d for Poas over ~ 0.734 km2, 3.8 ± 0.9 t/d over ~ 0.049 km2 for Irazus main crater, and 15 ± 12 t/d over 0.0059 km2 for Irazus north flank. Turrialba and Poas volcano diffuse degassing budget represent about 10\% of the whole gas output. Both volcanoes were in a transitional stage and the opening of new conduits may cause a loss in diffuse degassing and an increase of active degassing. Numerous diffuse degassing structures were also identified. One of which at Turrialba was closely associated with the collapse of a crater wall in 2014 during the initiation of a new period of heightened eruptive activity. Similar structures were also observed on the outer slopes of the west crater, suggesting strong alteration and perhaps destabilization of the upper outer cone. Irazus north flank is highly permeable and has experienced intense hydrothermal alteration.

Calderas Bottom‐to‐Top: An Online Seminar and Field Trip

Caldera-related processes have deep implications in Earth science and are important to the general public. To the geologist, calderas are surface manifestations of large magma reservoirs and the source of some of the largest eruptions on Earth. For society, these volcanoes represent not only an extreme volcanic hazard but also a potential source of abundant geothermal energy and metal ore deposits. During February–April 2009, an innovative, online course entitled “Calderas: Bottom-to-top” was offered across several universities to students interested in investigating caldera-forming processes associated with “supervolcanoes.” Supervolcanoes have the ability to spew hundreds to thousands of cubic kilometers of material from large magma chambers pooled in the Earths crust. A caldera-forming eruption results from overpressurization of the chamber and leads to formation of large depressions, tens of kilometers in diameter.

Using Drones and Miniaturized Instrumentation to Study Degassing at Turrialba and Masaya Volcanoes, Central America

Gas measurements using unmanned aerial vehicles, or drones, were undertaken at Turrialba volcano, Costa Rica, and Masaya volcano, Nicaragua, in 2016 and 2017. These two volcanoes are the largest time-integrated sources of gas in the Central American Volcanic Arc, and both systems are currently extremely active with potential for sudden destabilization. We employed a series of miniaturized drone-mounted instrumentation including a mini-DOAS, two MultiGAS instruments, and an optical particle counter, supplemented by ground-based measurements. Payloads were typically 1–1.5 kg and flight times were 10–15 min. The measurements were both accurate and precise due to the inherent sensitivity of the instrumentation and the high gas concentrations, which the drones were able to sample. The quality of data obtained by our drones was comparable to that obtained by our ground-based measurements. At Turrialba in April 2017, we measured an average SO2 flux of 1,380 ± 280 T/day, CO2/SO2 of 6.5, and H2O/SO2 of 27.8. Using these values, we calculated a CO2 flux of 6,170 T/day and an H2O flux of 10,790 T/day. At Masaya in May 2017, the average SO2 flux was 1,560 ± 180 T/day, with CO2/SO2 of 3.9 and H2O/SO2 of 62.3, giving a mean CO2 flux of 4,150 T/day andmean H2O flux of 27,330 T/day. The elevated carbon and water fluxes and ratios are indicative of underlyingmagmas that are enriched in these components, resulting in the high levels of activity observed.

Extremely high diversity of sulfate minerals in caves of the Irazú Volcano (Costa Rica) related to crater lake and fumarolic activity

This project was supported by Centro de Investigacion en Ciencias Geologicas of Universidad de Costa Rica (830-B7-A00) and the Costa Rican Department of Science and Technology (MICITT) fund FI-160B-14 to Andres Ulloa Carmiol.

New insights into the magmatic-hydrothermal system and volatile budget of Lastarria volcano, Chile: Integrated results from the 2014 IAVCEI CCVG 12th Volcanic Gas Workshop

Recent geophysical evidence for large-scale regional crustal inflation and localized crustal magma intrusion has made Lastarria volcano (northern Chile) the target of numerous geological, geophysical, and geochemical studies. The chemical composition of volcanic gases sampled during discrete campaigns from Lastarria volcano indicated a well-developed hydrothermal system from direct fumarole samples in A.D. 2006, 2008, and 2009, and shallow magma degassing using measurements from in situ plume sampling techniques in 2012. It is unclear if the differences in measured gas compositions and resulting interpretations were due to artifacts of the different sampling methods employed, short-term excursions from baseline due to localized changes in stress, or a systematic change in Lastarria’s magmatic-hydrothermal system between 2009 and 2012. Integrated results from a two-day volcanic gas sampling and measurement campaign during the 2014 International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Commission on the Chemistry of Volcanic Gases (CCVG) 12th Gas Workshop are used here to compare and evaluate current gas sampling and measurement techniques, refine the existing subsurface models for Lastarria volcano, and provide new constraints on its magmatic-hydrothermal system and total degassing budget. While compositional differences among sampling methods are present, distinct compositional changes are observed, which if representative of longterm trends, indicate a change in Lastarria’s overall magmatic-hydrothermal system. The composition of volcanic gases measured in 2014 contained high proportions of relatively magmaand water-soluble gases consistent with degassing of shallow magma, and in agreement with the 2012 gas composition. When compared with gas compositions measured in 2006–2009, higher relative H2O/CO2 ratios combined with lower relative CO2/St and H2O/St and stable HCl/St ratios (where St is total S [SO2 + H2S]) are observed in 2012 and 2014. These compositional changes suggest variations in the magmatichydrothermal system between 2009 and 2012, with possible scenarios to explain these trends including: (1) decompression-induced degassing due to magma ascent within the shallow crust; (2) crystallization-induced degassing of a stalled magma body; (3) depletion of the hydrothermal system GEOSPHERE GEOSPHERE; v. 14, no. 3 doi:10.1130/GES01495.1 12 figures; 6 tables; 2 supplemental files CORRESPONDENCE: tmlopez@ alaska .edu CITATION: Lopez, T., Aguilera, F., Tassi, F., de Moor, J.M., Bobrowski, N., Aiuppa, A., Tamburello, G., Rizzo, A.L., Liuzzo, M., Viveiros, F., Cardellini, C., Silva, C., Fischer, T., Jean-Baptiste, P., Kazayaha, R., Hidalgo, S., Malowany, K., Lucic, G., Bagnato, E., Bergsson, B., Reath, K., Liotta, M., Carn, S., and Chio dini, G., 2018, New insights into the magmatic-hydrothermal system and volatile budget of Lastarria volcano, Chile: Integrated results from the 2014 IAVCEI CCVG 12th Volcanic Gas Workshop: Geosphere, v. 14, no. 3, p. 983–1007, doi:10.1130/GES01495.1. Science Editor: Raymond M. Russo Guest Associate Editor: Shanaka de Silva Received 12 January 2017 Revision received 4 December 2017 Accepted 21 March 2018 Published online 7 May 2018

The Geothermal Resource in the Guanacaste Region (Costa Rica): New Hints From the Geochemistry of Naturally Discharging Fluids

The Guanacaste Geothermal Province (GGP) encompasses the three major volcanoes of northern Costa Rica, namely from NW to SE: Rincon de la Vieja, Miravalles and Tenorio. The dominant occurrence of (i) SO4-rich acidic fluids at Rincon de la Vieja, (ii) Cl-rich mature fluids at Miravalles and (iii) HCO3--rich and low-temperature fluids at Tenorio was previously interpreted as due to a north-to-south general flow of thermal waters and a magmatic gas upwelling mostly centered at Rincon de la Vieja, whereas Miravalles volcano was regarded as the typical geothermal system. The uniformity in chemical and isotopic (R/Ra and 34S) compositions of the neutral Cl-rich waters suggested to state that all the thermal discharges in the GGP are linked at depth to a single, regional geothermal reservoir. In this scenario, the thermal manifestations related to Tenorio volcano were regarded as a distal and diluted fluid outflow. In this study, a new gas geochemical dataset, including both chemical and isotopic (13C-CO2 and R/Ra) parameters of fluid discharges from the three volcanoes, is presented and discussed. Particular attention was devoted to the Tenorio thermal manifestations, since they were poorly studied in the past because this area has been considered of low geothermal potential. The aim is to provide insights into the magmatic-hydrothermal fluid circulation and, to verify the spatial distribution of the heat fluid source feeding the fluid manifestations. Our results only partially confirm the previously depicted model, because the geochemical and isotopic features (e.g. relatively high concentrations of temperature-dependent gases and high R/Ra values) shown by fluids seeping out from the southern sector of Tenorio volcano are more representative of medium-to-high enthalpy volcanic systems than those typically occurring in distal areas. This implies that the geothermal potential in the south of the GGP is higher than previously thought.

Renewed Explosive Phreatomagmatic Activity at Poás Volcano, Costa Rica in April 2017

Phreatic and phreatomagmatic eruptions at volcanoes often present no short term precursory activity, making them a challenge to forecast. Poás volcano, Costa Rica, exhibits cyclic activity with phreatic and some phreatomagmatic eruptions separated by times of quiescence. The latest phreatomagmatic stage began in March 2017 with increases in crater lake temperatures, SO2 flux, and the rate of seismicity, as well as accelerated ground inflation near the active crater. On 23 April 2017 at 04:12 UTC, a large phreatomagmatic eruption occurred at Poás, sending blocks up to 1 m in length to distances >1 km. Hindsight analysis revealed a precursory seismic sequence from 25 March to 22 April of similar seismic events (in terms of their frequency and waveform characteristics). Fourteen families of similar seismic events (containing ≥10 events per family) were identified during this precursory sequence, totaling over 1,300 events. An acceleration within the dominant family of LF (low frequency) waveforms was identified, suggesting that a forecast for the onset of the eruption may have been possible using the Failure Forecast Method (FFM). However, no confidence could be placed in the forecast generated, reiterating that not all accelerating trends are suitable for analysis using the FFM, in particular in conjunction with a least-squares linear regression. Our residual analysis further supports the concept that using a least-squares linear regression analysis is not appropriate with this dataset, and allows us to eliminate commonly used forecasting parameters for this scenario. However, the identification of different families of similar seismicity allows us to determine that magmatic fluid on its way to the surface initially became stalled beneath a chilled margin or hydrothermal seal, before catastrophically failing in a large phreatomagmatic eruption. Additionally, we note that 24 h prior to the large phreatomagmatic eruption, all LF families became inactive, which could have been falsely interpreted in real time as the waning of activity. Our results suggest that identifying families of seismicity offers unique opportunities to better understand ongoing processes at depth, and to challenge conventional forecasting techniques.