Bulletin of Volcanology最新文献

Turbulent air entrainment into explosive volcanic jets determines whether an eruption will produce buoyant plumes, pyroclastic density currents, or both. Most previous studies of entrainment consist of numerical models and analog laboratory experiments, with relatively few observations of natural eruptions. The existing observations of entrainment are generally time- and space-averaged measurements, which do not provide information regarding the mechanisms of entrainment. We investigate spatial and temporal variations in entrainment of the March 22 Plinian phase of the 1944 eruption of Mt. Vesuvius using a feature tracking velocimetry (FTV) algorithm applied to film collected by the U.S. Navy and digitized by the U.S. National Archives. We describe a novel technique to estimate the 3D plume morphology from normalized brightness. Projection of the 2D velocity fields from the FTV algorithm onto those 3D surfaces provides 3D velocity fields. The divergence of the velocity fields quantifies local expansion and entrainment and shows that although kilometer scale eddies are present in the plume, entrainment and expansion occur over length scales on the order of hundreds of meters. Integrating the inward directed velocities over the entraining regions quantifies local air entrainment rates. We find that entrainment of 5.4–6.1 × 10⁷ m³s^-1 air occurs over about one-third of the observed plume margins, yielding an average entrainment velocity of ~ 2.8 ms^-1. Extrapolation of those rates to the entire plume indicates total entrainment of 1–3 × 10⁸ m³s^-1. The entrainment velocity has a magnitude ~ 6% of the magnitude of the turbulence intensity along the plume margins, indicating that the latter may approximate the centerline plume velocity and suggesting use of entrainment coefficient of 0.06 for this and similar eruptions, i.e., strong plumes with a relatively high momentum-dominated region.

While 80% of tsunamis are related to earthquakes, recent examples of the Hunga Tonga Hunga Ha’apai (2022) tsunami as well as others from the Kick’em Jenny (2015), Saint Vincent (2021), and La Palma (2021) eruptions have sparked renewed reflection on how a tsunami warning system could also handle non-seismic tsunami events. A warning system is usually based on intrinsic and automatic detection by an instrumental network. In the case of tsunamis generated by earthquakes, it is the data from seismic stations and pre-established location and magnitude criteria that trigger actions from the Tsunami Service Providers (TSP, i.e., regional centers for threat information). Realtime sea level data then help constrain forecasts and determine the end of the threat. However, tsunamis generated by volcanic events are different from those induced by earthquakes in terms of source, detection, messaging, and modeling. In the Caribbean and Adjacent Regions, the UNESCO/IOC Intergovernmental Coordination Group for Tsunami and other Coastal Hazards Warning Systems created a task team to develop tsunami procedures in the case of a volcano crisis. We present here the recent progress of the task team. A bulletin is proposed to be issued by volcano observatories to the Tsunami Service Providers in the case of a potentially tsunamigenic volcano event. Derived from a Volcano Observatory Notice for Aviation (VONA) bulletin, this proposed VONUT bulletin, (Volcano Observatory Notice for tsUnami Threat), is under construction in collaboration with Caribbean volcano observatories and the Pacific Tsunami Warning Center, the TSP for the Caribbean. It was tested during the annual tsunami exercise CARIBE WAVE 2023, which includes testing the communications between the Tsunami Service Provider and nationally designated tsunami authorities. However, much more work is required to get a full operating warning system, as volcano scenarios and subsequent tsunami waves remain highly challenging to model and scale.

The Genbudo lava, the late Pleistocene basaltic-andesitic lava flow in the southwestern part of Iwate Volcano, Japan, is a 70 m thick columnar jointed flow that can be divided into three parts from bottom to top: the colonnade, the entablature, and the partly-brecciated uppermost part. Two main types of fractures developed in the entablature: pseudopillow fractures that formed in a branching network-like pattern throughout the entablature, and sheet fractures with curved surfaces that are nearly parallel to each other. At the uppermost part of the flow, finger-like structures of lava extend upward from the coherent lava, and cogenetic autoclastic rocks form between the fingers. This occurrence suggests that hyaloclastites were generated during emplacement in the uppermost part of the flow, apparently when water from a dammed river valley covered the flow. The texture of the lava near the pseudopillow fractures in the entablature is commonly hypocrystalline, while the texture in other parts is holocrystalline. There are two types of pyroxene microlites, large prismatic (average size ~ 30 µm) and dendritic (< 10 µm in length) crystals in the lava near the pseudopillow fractures. These suggest that the cooling rate of the lava was greatest in the vicinity of the pseudopillow fractures. Networks of palagonite-filled micro-fractures (less than 10 µm in width) are found in this part of the flow, and many bubbles are observed along the fractures. This is clear evidence that the rapid cooling of the lava was caused by water infiltration through the pseudopillow fractures. From the measurement of Fe-rich droplet sizes that formed due to liquid immiscibility within the lava, we estimate the cooling rate within the colonnade as about 49 °C/h and within the entablature as 642 °C/h, consistent with much more rapid cooling by water infiltration from above.

Tectonic controls on dyke emplacements, eruption dynamics and locations have been observed in multiple volcanic areas worldwide. Mapping of active structures is therefore key for assessing potential tectonic and volcanic hazards in active regions. We used wrapped interferograms from the TerraSAR-X satellite to map active fracture movements over a 2-year period of a volcano-tectonic unrest at the onshore Reykjanes Peninsula plate boundary in SW Iceland. As of 1 December 2023, the unrest has included at least six inflation events and five dyke injections resulting in three eruptions of the Fagradalsfjall volcanic segment. In addition to the deformation associated with the 2019–2021 inflation events and intrusions, the interferograms reveal fracture movements over a wide area surrounding the active plate boundary segment. This first-order mapping of active fractures complements previously mapped structures, as InSAR allows for the detection of subtle ground movements, even in areas where young lava flows cover older structures. Our fracture data therefore fill in some of the apparent voids in previous fracture and fault maps of SW Iceland. Furthermore, our investigation reveals aseismic movement on previously unknown fractures directly beneath the town of Grindavík, as well as a N45(^circ ) E striking fracture co-located with the longest lasting volcanic vent of the subsequent 2021 eruption. The mapping method we present in this study is relevant for active volcano-tectonic regions where InSAR can be applied to detect small-scale fracture movements to advance understanding of ongoing unrest and volcano-tectonic hazards.

Magma ascent rate can control the hazard potential of an eruption, but it is difficult to directly determine. Here we investigate the variations in timescales and rates of magma ascent for the three most recent explosive and effusive eruptions of Kelud volcano in Indonesia (1990, 2007, and 2014) using the zoning of volatile elements (OH, Cl, F) in apatite. We found that crystals from the 2007 dome show chemical gradients and increasing concentrations (reverse zoning) in chlorine and/or fluorine towards the crystals’ rims whereas those of the 1990 and 2014 explosive eruptions are unzoned. Diffusion modelling of the volatile elements in zoned apatite of the 2007 dome rocks give magma ascent times of up to 3 months, although 65% of them are ≤ 60 days. In contrast, the maximum magma ascent timescales inferred from apatite of the 1990 and 2014 explosive eruptions are 7–8 h. Using the pre-eruptive magma storage depths obtained from petrological and phase equilibria studies, we calculate ascent rates > 0.4 × 10^–3 m s⁻¹ for the 2007 dome, and > 3.0 × 10^–1 m s⁻¹ for the 1990 and 2014 eruptions. We also calculated the magma viscosities for each eruption (1990: 10^3.8–9.3 Pa s; 2007: 10^6.4–13.3 Pa s; 2014: 10^3.6–8.7 Pa s), which when combined with the magma ascent rates and magma mass discharge rates correspond well with the expected eruptive styles. Our study illustrates the robustness of modelling apatite zoning in volatile elements to constrain timescales and magma ascent dynamics, and highlights the important role of magma ascent on eruptive styles.

The simultaneous or sequential occurrence of several hazards—be they of natural or anthropogenic sources—can interact to produce unexpected compound hazards and impacts. Since success in responding to volcanic crises is often conditional on accurate identification of spatiotemporal patterns of hazard prior to an eruption, ignoring these interactions can lead to a misrepresentation or misinterpretation of the risk and, during emergencies, ineffective management priorities. The 2021 eruption of Tajogaite volcano on the island of La Palma, Canary Islands (Spain), was an 86 day-long hybrid explosive-effusive eruption that demonstrated the challenges of managing volcanic crises associated with the simultaneous emission of lava, tephra and volcanic gases. Here, we present the result of a small-scale impact assessment conducted during three-field deployments to investigate how tephra fallout and lava flow inundation interacted to cause compound physical impact on buildings. The study area was a neighbourhood of 30 buildings exposed to tephra fallout during the entire eruption and by a late-stage, short-lived lava flow. Observations highlight, on one hand, the influence of clean-up operations and rainfall on the impact of tephra fallout and, on the other hand, the importance of the dynamics of lava flow emplacement in controlling impact mechanisms. Overall, results provide an evidence-based insight into impact sequences when two primary hazards are produced simultaneously and demonstrate the importance of considering this aspect when implementing risk mitigation strategies for future long-lasting, hybrid explosive-effusive eruptions in urban environments.

We studied four Quaternary volcanic phonolitic explosive edifices on Petite-Terre Island (Mayotte, Comoros Archipelago, Western Indian Ocean) to quantify magma fragmentation processes and eruptive dynamics. Petite-Terre explosive volcanism is the westernmost subaerial expression of a 60-km-long volcanic chain, whose eastern tip was the site of the 2018–2020 submarine eruption of the new Fani Maoré volcano. The persistence of deep seismic activity and magmatic degassing along the volcanic chain poses the question of a possible reactivation on land. Through geomorphology, stratigraphy, grain size, and componentry data, we show that Petite-Terre “maars” are actually tuff rings and tuff cones likely formed by several closely spaced eruptions. The eruptive sequences of each edifice are composed of thin (cm–dm), coarse, lithic-poor pumice fallout layers containing abundant ballistic clasts, and fine ash-rich deposits mostly emplaced by dilute pyroclastic density currents (PDCs). Deposits are composed of vesiculated, juvenile fragments (pumice clasts, dense clasts, and obsidian), and non-juvenile clasts (from older mafic scoria cones, coral reef, the volcanic shield of Mayotte, as well as occasional mantle xenoliths). We conclude that phonolitic magma ascended directly and rapidly from depth (around 17 km) and experienced a first, purely magmatic fragmentation, at depth (≈ 1 km in depth). The fragmented pyroclasts then underwent a second shallower hydromagmatic fragmentation when they interacted with water, producing fine ash and building the tuff rings and tuff cones.

Volcanic ash provides unique pieces of information that can help to understand the progress of volcanic activity at the early stages of unrest, and possible transitions towards different eruptive styles. Ash contains different types of particles that are indicative of eruptive styles and magma ascent processes. However, classifying ash particles into its main components is not straightforward. Diagnostic observations vary depending on the magma composition and the style of eruption, which leads to ambiguities in assigning a given particle to a given class. Moreover, there is no standardized methodology for particle classification, and thus different observers may infer different interpretations. To improve this situation, we created the web-based platform Volcanic Ash DataBase (VolcAshDB). The database contains > 6,300 multi-focused high-resolution images of ash particles as seen under the binocular microscope from a wide range of magma compositions and types of volcanic activity. For each particle image, we quantitatively extracted 33 features of shape, texture, and color, and petrographically classified each particle into one of the four main categories: free crystal, altered material, lithic, and juvenile. VolcAshDB (https://volcash.wovodat.org) is publicly available and enables users to browse, obtain visual summaries, and download the images with their corresponding labels. The classified images could be used for comparative studies and to train Machine Learning models to automatically classify particles and minimize observer biases.