Bulletin of Volcanology最新文献

Nyiragongo is one of the eight volcanoes of the Virunga volcanic chain located in the western branch of the East African Rift, more specifically in eastern Democratic Republic of Congo (DRC). The volcano's lava flows pose a threat to the city of Goma. Here we present seismographic, geothermal and petrographic data related to the May-June 2021 unrest and eruption of Nyiragongo. Seismicity was low prior to the eruption, with a daily average of 11 earthquakes from January 1 to May 22, 2021, the day of the eruption. Seismicity increased on May 22 2021, when the eruption began. During May 23 to September 28, 2021 the daily average number of earthquakes rose from 11 to 57 with the daily number of detected earthquakes peaking between May 22 and June 3, 2021. Prior to the eruption there was a moderate increase in ground temperature at the southern sites from February 27 to June 15 2021, but stability at the northern sites close to the volcano, and a constant radiant heat output from the crater. After the eruption, ground temperatures dropped from 23.5°C to 22.8°C; 23.7°C to 21.9°C from June 12 to June 20 2021 at the southern sites and from 26.0 °C to 24.5°C from May 26 to May 30 2021 at northern sites. The lava is glassy, with a low phenocryst content. The phases present in the basalt are: clinopyroxene, plagioclase, olivine and opaque minerals. In the foidites, the mineral phases are clinopyroxenes, plagioclases, nepheline and haüyne.

The Paraná-Etendeka Large Igneous Province (PELIP) is renowned for its massive and rapidly emplaced flood basalts that dominated the centre of the Gondwana supercontinent during the Early Cretaceous. However, little is currently understood about mafic explosive eruptions, which often occur simultaneously with effusive activity, as observed in young basaltic volcanism. Here, we describe the first well-preserved layer of basaltic tuff interbedded within the high-Ti basaltic lava sequence in the central part of the PELIP, Brazil. The Tapalam Tuff consists of basaltic juvenile glassy components, scoriaceous lapilli and coarse ash, with a cement containing clays, zeolites, carbonates, and iron oxides. The glassy sideromelane fragments range from well-rounded achneliths with smooth, curved surfaces to highly angular, cuspate-shaped or platy shards. Achnelith morphologies include broken droplets (Pele’s tears), thread fragments (Pele’s hair), dumbbells, needles, spheres, ovoids and reticulite. Elongated pyroclasts exhibit a flat orientation, and subtle bedding is defined by granulometric alternation. Our findings suggest the deposits were laid down proximal to the volcanic vent and likely indicate a fallout deposit associated with a fluid-dominated, high (hundreds of meters or more than 1 km) fountain similar to a Hawaiian-type eruption, fed by low-viscosity basaltic magma. Volcanic activity was therefore not exclusively effusive but also involved explosive eruptions, which may have significant implications for understanding PELIP’s volcanic history and its relation to local and global environmental changes.

Owing to the current lack of plausible and exhaustive physical pre-eruptive models, often volcanologists rely on the observation of monitoring anomalies to track the evolution of volcanic unrest episodes. Taking advantage from the work made in the development of Bayesian Event Trees (BET), here we formalize an entropy-based model to translate the observation of anomalies into probability of a specific volcanic event of interest. The model is quite general and it could be used as a stand-alone eruption forecasting tool or to set up conditional probabilities for methodologies like the BET and of the Bayesian Belief Network (BBN). The proposed model has some important features worth noting: (i) it is rooted in a coherent logic, which gives a physical sense to the heuristic information of volcanologists in terms of entropy; (ii) it is fully transparent and can be established in advance of a crisis, making the results reproducible and revisable, providing a transparent audit trail that reduces the overall degree of subjectivity in communication with civil authorities; (iii) it can be embedded in a unified probabilistic framework, which provides an univocal taxonomy of different kinds of uncertainty affecting the forecast and handles these uncertainties in a formal way. Finally, for the sake of example, we apply the procedure to track the evolution of the 1982–1984 phase of unrest at Campi Flegrei.

The Instituto Geofísico (IG-EPN) was created in 1983 by faculty of the Escuela Politécnica Nacional, a public university in Quito, Ecuador, with the objective of assessing volcanic hazard in the country. Since then, the IG-EPN has established and developed an instrumental monitoring network and from 1999 has faced the eruption of five continental-arc volcanoes (Guagua Pichincha, Tungurahua, Reventador, Cotopaxi, and Sangay) which displayed varied hazards, eruptive dynamics, eruption durations, and socio-economic contexts. At the same time, mainly effusive eruptions took place in Galápagos archipelago, which has undergone an increase in local population over the last two decades and hence in the risk posed by volcanic eruptions. The outstanding handling of these volcanic crises was the reason why IG-EPN was granted with the 2020 Volcanic Surveillance and Crisis Management IAVCEI Award. Now, the IG-EPN manages a country-wide network of about 500 instruments to monitor both volcanic and tectonic activity with a highly qualified staff of 80 people. This manuscript describes the history of IG-EPN, the main volcanic hazard studies and resulting hazard maps; the instrumental networks; and the volcanic crises that the IG-EPN faced during the last forty years.

Effective risk management requires accurate assessment of population exposure to volcanic hazards. Assessment of this exposure at the large-scale has often relied on circular footprints of various sizes around a volcano to simplify challenges associated with estimating the directionality and distribution of the intensity of volcanic hazards. However, to date, exposure values obtained from circular footprints have never been compared with modelled hazard footprints. Here, we compare hazard and population exposure estimates calculated from concentric radii of 10, 30 and 100 km with those calculated from the simulation of dome- and column-collapse pyroclastic density currents (PDCs), large clasts, and tephra fall across Volcanic Explosivity Index (VEI) 3, 4 and 5 scenarios for 40 volcanoes in Indonesia and the Philippines. We found that a 10 km radius—considered by previous studies to capture hazard footprints and populations exposed for VEI ≤ 3 eruptions—generally overestimates the extent for most simulated hazards, except for column collapse PDCs. A 30 km radius – considered representative of life-threatening VEI ≤ 4 hazards—overestimates the extent of PDCs and large clasts but underestimates the extent of tephra fall. A 100 km radius encapsulates most simulated life-threatening hazards, although there are exceptions for certain combinations of scenario, source parameters, and volcano. In general, we observed a positive correlation between radii- and model-derived population exposure estimates in southeast Asia for all hazards except dome collapse PDC, which is very dependent upon topography. This study shows, for the first time, how and why concentric radii under- or over-estimate hazard extent and population exposure, providing a benchmark for interpreting radii-derived hazard and exposure estimates.

The Vedde Ash, originating from the Katla central volcano, Iceland, and taken to be dispersed across the North Atlantic and Europe at ~ 12 ka BP, is widely used as a geochronological marker. However, distal tephra layers with compositions like the Vedde Ash but of younger ages question the reliability of Vedde-like tephra layers as robust age control. Vedde-like tephra layers are rare in Icelandic sedimentary sequences and, where present, lack firm age control. Providing well-constrained local records of Early Holocene Katla layers is therefore critical to assess uncertainties related to the use of the Vedde Ash. Here we report three visible and stratigraphically separated Early Holocene Katla tephra layers from Torfdalsvatn, a lake in north Iceland, each with chemistry similar to the Vedde Ash. Using high-resolution ¹⁴C chronologies, we provide ages (± 1σ) for these tephra layers of 11,315 ± 180, 11,295 ± 195, and 11,170 ± 195 cal a BP. These observations reinforce that multiple explosive eruptions of Katla occurred over a 1000-year interval in the Early Holocene and challenge the precision of some paleoclimate records using the Vedde Ash as a geochronometer where age control is equivocal. This may lead to a re-evaluation of age models for some Early Holocene North Atlantic records.

El Negrillar volcanic field has the largest extent and erupted volume (~ 6.8 km³ DRE) of all the monogenetic centers of the Andean Central Volcanic Zone (CVZ). The volcanic field comprises 51 eruptive centers and 98 lava flows distributed in three clusters: Northern El Negrillar (NEN), Central El Negrillar (CEN), and Southern El Negrillar (SEN). Here, we present a geological map of El Negrillar, with detail of effusive and explosive volcanic deposits not previously mapped in the southern sector of the CEN and SEN clusters. Ten samples of El Negrillar’s deposits associated with effusive and phreatomagmatic activity were dated using ⁴⁰Ar/³⁹Ar geochronology, establishing, along with previously published dates, a geochronological characterization of the development of El Negrillar’s monogenetic field. The collected age data yields a range of 0.982 ± 0.008 to 0.141 ± 0.072 Ma, compared to previously published K–Ar ages for the same deposits range from < 1.5 Ma to 0.6 ± 0.4 Ma. The new ages presented here indicate that the effusive activity at El Negrillar (NEN, CEN, and SEN), and the phreatomagmatic activity in the CEN (dated for first time) occurred quasi-simultaneously (within error). The end of the volcanic activity within the monogenetic field occurred in the eastern sector of the CEN at 0.141 ± 0.072 Ma, which represents the youngest eruption ages of El Negrillar. If these new ages are revisited within the regional context of the SW sector of the Altiplano-Puna Volcanic Complex (APVC), the monogenetic volcanoes appear to be the result of a migration of mafic vents along a southwest-northeast trend, as shown by their age variation from the oldest to the youngest volcanic center: Morro Punta Negra, La Negrillar, El Negrillar, Tilocálar Sur, Tilocálar Norte, Cerro Tujle, El País, Puntas Negras, La Albóndiga Grande, and Cerro Overo. These results highlight the structural control on the emplacement of monogenetic mafic volcanism in the APVC.

Eruptions from Mauna Loa’s Southwest Rift Zone (SWRZ) pose a significant threat to nearby communities due to high eruption rates and steep slopes resulting in little time for evacuation. Despite the large body of research done on Mauna Loa, knowledge of the timing and duration of magma residence and transfer through its internal plumbing system is still poorly constrained. This study presents a first quantitative look at thermochemical conditions and timescales of potentially deep storage and disaggregation of magmatic mush during the run-up to the voluminous 1950 AD SWRZ eruption. Details of heterogeneous compositions and textures of the macrocryst and glomerocryst cargo in 1950 AD lavas suggest magma mixing and crystal recycling along the entire plumbing system. Furthermore, the crystal cargo contains evidence for the direct interaction between primitive, deeply stored magma and pockets of more evolved magma stored at shallow to intermediate depths. An enigmatic attribute of 1950 near-vent lava is the near-ubiquitous presence of subhedral, unreacted Mg-rich orthopyroxene phenocrysts (Mg#>80). Phase relations of Mauna Loa olivine-tholeiite indicate that orthopyroxene joins olivine as a primary phase at pressures higher than 0.6 GPa. Coexisting Mg-rich olivine and orthopyroxene and the occurrence of harzburgitic (olivine-orthopyroxene) glomerocrysts provide evidence for cognate crystallisation at near-Moho (~ 18 km) depths (Thornber and Trusdell 2008). Petrogenetically diverse populations of glomerocrysts and macrocrysts alongside evidence of multilevel magma storage indicate a network of ephemeral and possibly interconnected magma pockets from near-Moho depths to the upper/mid-crust. Fe-Mg diffusion chronometry applied to 1950 AD olivine populations implies rapid mobilisation and transport of large volumes of magma (376×10⁶ m³) from near-Moho storage to the surface within less than 8 months, with little residence time (~ 2 weeks) in the shallow (3–5 km) plumbing system.

Volcano geodesy often involves the use of models to explain observed surface deformation. A variety of forward models are used, from analytical point sources to numerical simulations that consider complex magma system geometries, topography, and material properties. Various inversion methods can then be used to relate observed volcano data to models. Ideally, forward models should be verified through intercomparison, to check for implementation errors and quantify the error induced by any approximations used. Additionally, forward models and inversion methods should be validated through tests with synthetic and/or real data, to determine their ability to match data and estimate parameter values within uncertainty. However, to date, there have not been comprehensive verification and validation efforts in volcano geodesy. Here, we report on the first phase of the Drivers of Volcano Deformation (DVD) exercises, which were designed to build community involvement through web-based exercises involving calculations of static elastic displacement around pressurized magma reservoirs. The forward model exercises begin with a spherical reservoir in a homogeneous half space, then introduce topography, heterogeneous elastic properties, and spheroidal geometries. The inversion exercises provide synthetic noisy surface displacement data for a spherical reservoir in a homogeneous half space and assess consistency in estimates of reservoir location and volume/pressure change. There is variability in the results from both forward modeling and inversions, which highlights the strengths and limitations of different forward models, as well as the importance of inversion method choice and uncertainty quantification. This first phase of the DVD exercises serves as a community resource and will facilitate further efforts to develop standards of reproducibility.

Dykes and sills occupy Mode I (extension), Mode II (shear), or hybrid mode fractures and most of the time transport and store magma from deep reservoirs to the surface. Subject to their successful propagation, they feed volcanic eruptions. Yet, dykes and sills can also stall and become arrested as a result of the crust’s heterogeneous and anisotropic characteristics. Dykes can become deflected at mechanical discontinuities to form sills, and vice versa. Although several studies have examined dyke propagation in heterogeneous and anisotropic crustal segments before, the conditions under which dykes propagate in glacial-volcanotectonic regimes remain unclear. Here, we coupled field observations with 2D FEM numerical modelling to explore the mechanical conditions that encourage (or not) dyke-sill transitions in volcanotectonic or glacial settings. We used as a field example the Stardalur cone sheet-laccolith system, which lies on the Esja peninsula, close to the western rift zone, NW of the southern part of the Icelandic rift. The laccolith is composed of several vertical dykes that transition into sills and form a unique stacked sill ‘flower’ structure. Here, we investigate whether the Stardalur laccolith was formed under the influence of stresses caused by glacial retreat due to thickness variations (0–1 km) in addition to regional and local tectonic stresses (1–3 MPa extension or compression) and varied magma overpressure (1–30 MPa), as well as the influence of the mechanical properties of the lava/hyaloclastite contact. Our results show that the observed field structure in non-glacial regimes was formed as a result of either the mechanical (Young’s modulus) contrast of the lava/hyaloclastite contact or a compressional regime due to pre-existing dykes or faulting. In the glacial domain, the extensional stress field below the ice cap encouraged the formation of the laccolith as the glacier became thinner (subject to a lower vertical load). In all cases, the local stress field influenced dyke to sill deflection in both volcanotectonic regimes.