Insights into the mechanisms of phreatic eruptions from continuous high frequency volcanic gas monitoring: Rinc\uf3n de la Vieja Volcano, Costa Rica

Understanding the trigger mechanisms of phreatic eruptions is key to mitigating the effects of these hazardous but poorly forecastable volcanic events. It has recently been established that high-rate volcanic gas observations are potentially very suitable to identifying the source processes driving phreatic eruptions, and to eventually detecting precursory changes prior to individual phreatic blasts. In February-May 2017, we deployed a Multi-GAS instrument to continuously monitor gas concentrations in the crater lake plume of Rincon de la Vieja, a remote and poorly monitored active volcano in Costa Rica, site of frequent phreatic/phreatomagmatic eruptions. Forty-two phreatic/phreatomagmatic eruptions were seismically recorded during our investigated period, 9 of which were also recorded for gas by the Multi-GAS. To the best of our knowledge, these represent the first instrumentally measured gas compositions during individual phreatic/phreatomagmatic explosions at an active volcano. Our results show that during background quiescent degassing the Rincon de la Vieja crater lake plume was characterized by high CO2/SO2 ratios of 64 +/- 59 and H2S/SO2 ratios of 0.57 +/- 0.20. This composition is interpreted as reflecting hydrothermal (re) processing of magma-sourced gas in the sub-limnic environment. Phreatic blasts were recorded by the Multi-GAS as brief (1-2min long) pulses of elevated gas mixing ratios (up to similar to 52 ppmv SO2 and > 3,000 ppmv CO2), or more than an order of magnitude higher than during background degassing (similar to 1 ppmv SO2 and similar to 450 ppmv CO2). During the phreatic eruption(s), the H2S/SO2 ratio was systematically lower (< 0.18) than during background degassing, but the CO2/SO2 ratio remained high (and variable), ranging from 37 to 390. These S-poor compositions for the eruptive gas imply extensive processing of the source magmatic gas during pre-eruptive hydrothermal storage, likely by deposition of native S and/or sulfate. Our gas results are thus overall consistent with a mechanismof phreatic eruptions triggered by accumulation of magmatic-hydrothermal gases beneath a hydrothermal seal. We claim that real-time Multi-GAS monitoring is urgently needed at other crater lake-hosting volcanoes (e.g., Ruapehu, Aso), where phreatic eruptions may similarly be preceded by phases of reduced S degassing at the surface

SEISMIC ANISOTROPY AND TIME-FREQUENCY ANALYSES DURING TAUPŌ'S 2019 UNREST

The currently active Taupō volcano (with its most recent eruptive event at ∼ 1.8 ka) was responsible for Earth’s youngest supereruption at 25.5 ka. In the past 141 years, 21 unrest events have been observed in records of seismicity, crustal deformation and changes in the lake level at Taupō. The most recent unrest was during September 2018 – September 2019, and was interpreted to be caused by a magmatic intrusion rather than by hydrothermal instabilities in the volcano (Illsley-Kemp et al., 2021). Prior seismic anisotropy studies in the North Island have identified a distinct pattern of S-wave fast orientations at Taupō volcano that do not align with the maximum horizontal stress in the region. Therefore, due to the complexity of the unrest of the caldera, we combined seismic anisotropy and time-frequency analysis to complement the current understanding of volcano dynamics over the period of unrest. We used an existing 10-year earthquake catalogue determined by Illsley-Kemp et al. (2021) to study seismic anisotropy around Lake Taupō, with a focus on temporal analysis during the unrest period. Using 35,452 high quality shear-wave splitting measurements, we obtained the median fast orientation values for 23 seismic stations around Taupō. We recognised three significant anisotropy temporal changes during the unrest period, not related to variations in the travel path of the earthquakes, and interpreted these as stress-induced changes due to magmatic processes, in accordance with the findings of Illsley-Kemp et al. (2021). Temporal stress-changes identified by seismic anisotropy were compared with the results of time-frequency analysis to determine that the magmatic intrusion did not reach shallower depths. We reviewed the continuous stream of seismic data in the time-frequency domain to identify possible low frequency signals related to volcanic activity and to compare their relationship with stress changes during the unrest period. Even though we did not identify low frequency volcanic seismic signals during 2019, we propose a preliminary catalogue of typical low frequency seismic signals at Taupō, which includes the lake microseism signal. Volcanic unrest in calderas is a frequently occurring phenomenon, and does not always imply a volcanic eruption. The improvement of monitoring techniques will allow us to understand periods of unrest in calderas for volcano preparedness and risk management.</p

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, Poás, and Irazú, 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 ∼113 ± 46 t/d over ∼0.705 km2 for Turrialba, 0.9 ± 0.5 t/d for Poás over ∼0.734 km2, 3.8 ± 0.9 t/d over ∼0.049 km2 for Irazú’s main crater, and 15±12 t/d over 0.0059 km2 for Irazú’s north flank. Turrialba and Poás volcano diffuse degassing budget represent about 10% of the whole gas output. Both volcanoes were in a transitional stage 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, Poás, and Irazú, 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 ∼113 ± 46 t/d over ∼0.705 km2 for Turrialba, 5.8 ± 0.5 t/d for Poás over ∼0.734 km2, 3.8 ± 0.9 t/d over ∼0.049 km2 for Irazú’s main crater, and 15 ± 12 t/d over 0.0059 km2 for Irazú’s north flank. Turrialba and Poás volcanoes diffuse degassing budgets represent about 10% of 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. At Turrialba, one of which 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. Irazú’s north flank is highly permeable and has experienced intense hydrothermal alteration.Frontiers in Earth Scienc

The National Seismological Network of Costa Rica (RSN): An Overview and Recent Developments

The National Seismological Network of Costa Rica (RSN) is a joint effort between the University of Costa Rica (UCR) and the Costa Rican Institute of Electricity (ICE). In this article, we briefly describe its history, contributions, and seismic catalog. We also address recent developments, such as the expansion of the station network, the improvement on earthquake locations, and the use of new communication channels to share earthquake information. The RSN seismic catalog contains almost 123,000 earthquakes recorded since 1974. The geographical distribution of the local seismicity highlights plate boundaries as well as regions located along the inland projection of several bathymetric highs in the Cocos plate. In 2015, 70 new short‐period seismometers were installed to provide a new configuration with higher station density in central Costa Rica. Also, earthquake locations were improved by integrating routines from the SeisComP, EarthWorm, and SEISAN software packages. Additionally, several tools for disseminating earthquake information were developed, for example, an application for smartphones released in 2015 and a new website created in 2017. The RSN is also using Facebook and Twitter to engage and educate nonscientific audiences.Universidad de Costa Rica/[113-B5-704]/UCR/Costa RicaUniversidad de Costa Rica/[113-B5-A02]/UCR/Costa RicaUniversidad de Costa Rica/[113-A1-716]/UCR/Costa RicaUniversidad de Costa Rica/[ED-3005]/UCR/Costa RicaInstituto Costarricense de Electricidad/[]/ICE/Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela Centroamericana de Geologí

Peligro y vigilancia volcánica en Costa Rica

Costa Rica hosts ten volcanic complexes and is highly tectonically active due to its location at the interaction between the Cocos, Nazca, and Caribbean plates and the Panama microplate. Three of the five historically active volcanoes had frequent eruptions in 2019. The institutions in charge of monitoring the volcanoes of Costa Rica are the Observatorio Vulcanológico y Sismológico de Costa Rica from Universidad Nacional (OVSICORI-UNA) and the Red Sismológica Nacional (RSN: UCR-ICE that groups the Escuela Centroamericana de Geología from the Universidad de Costa Rica, and the Observatorio Sismológico y Vulcanológico de Arenal y Miravalles from the Instituto Costarricense de Electricidad; acronyms ECG, UCR, OSIVAM, and ICE). These institutions are focused on the most dangerous volcanoes, i.e. those closest to the Great Metropolitan Area (2.2 million inhabitants), which includes San José (the capital), and those near hydroelectrical and geothermal plants. In 2020, those institutions operated a network of. 59 seismic stations on volcanoes, 5 infrasound stations, 25 permanent GPS sites, 2 permanent DOAS, 3 permanent MultiGAS, 13 webcams, and performed systematic analyses in geochemistry and petrology laboratories. Those institutes routinely communicate results with the authorities in charge of crisis management nationally and internationally (Comisión Nacional de Prevención de Riesgos y Atención de Emergencias and Volcanic Ash Advisory Centre, respectively) and are always looking for more scientific collaborations.Costa Rica alberga diez complejos volcánicos y presenta una elevada actividad sísmica debido a su ubicación dentro de un marco tectónico complejo, donde interactúan las placas del Cocos, Nazca, Caribe y la microplaca de Panamá. Tres de los cinco volcanes históricamente activos han tenido frecuentes erupciones durante el 2019. Los institutos que vigilan los volcanes de Costa Rica son el Observatorio Vulcanológico y Sismológico de Costa Rica (OVSICORIUNA) y la Red Sismológica Nacional (RSN: UCR-ICE que agrupa a la Escuela Centroamericana de Geología de la Universidad de Costa Rica y al Observatorio Sismológico y Vulcanológico del Arenal y Miravalles del Instituto Costarricense de Electricidad, acrónimos en orden: ECG, UCR, OSIVAM e ICE). Estos institutos se enfocan principalmente en los volcanes que representan un alto riesgo para la capital San José y la Gran Área Metropolitana, en el centro de Costa Rica (2.2 millones de habitantes), y aquellos cerca de centrales hidroeléctricas y geotérmicas. La vigilancia se apoya en una red de 59 estaciones sísmicas, 5 medidores de infrasonido, 25 sitios GPS permanentes, 2 DOAS, 3 MultiGAS permanentes, 13 cámaras web y análisis sistemático de muestras en los laboratorios de geoquímica y petrología. Estas instituciones comunican sus resultados de forma rutinaria a las autoridades a cargo de la gestión de peligros nacionales e internacionales (Comisión Nacional de Prevención de Riegos y Atención de Emergencias y Volcanic Ash Advisory Centre, respectivamente), y permanecen en la búsqueda permanente de colaboraciones científicas.Observatorio Vulcanológico y Sismológico de Costa Rica de la Universidad Nacional de Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela Centroamericana de Geologí