Bulletin of Volcanology最新文献

The Southern Volcanic Zone (SVZ) in Chile is an active continental arc with a complex history of volcanism, where a range of magmatic compositions have been erupted in a variety of styles. In the Central SVZ, both monogenetic and polygenetic volcanoes exist, in close proximity to the Liquiñe-Ofqui Fault System (LOFS), but with variable local stress states. Previous studies have inferred varying crustal storage timescales, controlled by the orientation of volcanic centres relative to the N-S striking LOFS and σ_HMax in this region. To assess the relationship between volcanism and crustal stress states affected by large-scale tectonic structures and edifice controls, we present whole rock geochemical data, to ensure consistency in source dynamics and crustal processing, mineral-specific compositional data, thermobarometry, and Fe–Mg diffusion modelling in olivine crystals from mafic lavas, to assess ascent timescales, from the stratovolcanic edifice of Puyehue-Cordón Caulle and proximal small eruptive centres. Textural observations highlight differences in crystal maturation timescales between centres in inferred compression, transpression, and extension, yet source melting dynamics remain constant. Only samples from the stratovolcanic edifice (in regional compression) preserve extensive zonation in olivine macrocrysts; these textures are generally absent from proximal small eruptive centres in transtension or extension. The zonation in olivines from stratovolcanic lavas yields timescales on the order of a few days to a few weeks, suggesting that even in environments which inhibit ascent, timescales between unrest and eruption of mafic magmas may be short. Significantly, high-resolution compositional profiles from olivine grains in the studied samples record evidence for post-eruptive growth and diffusion, highlighting the importance of careful interpretation of diffusion timescales from zoned minerals in more slowly cooled lavas when compared with tephra samples.

Because dike propagation depends on stress state, the geometry of dikes can be used to make inferences about crustal stress conditions during emplacement. Early work relied on analytical solutions for stress in a two-dimensional elastic medium with a pressurized circular magma chamber and biaxial far-field stress. The principal stress trajectories in this classical model depend on the ratio of deviatoric stress magnitude to chamber pressure. Assuming dikes follow principal stress trajectories and bounding plausible magma chamber excess pressures lead to estimates of deviatoric stress magnitudes from the map pattern of dikes. Mériaux and Lister (2002) pointed out that this approach ignored stresses due to the magma-filled dikes themselves, which significantly alter predicted dike trajectories. They estimated deviatoric stresses 2 to 5 times previous estimates. However, Mériaux and Lister (2002) assumed the pressure distribution within the dike rather than computing it from viscous magma flow. We revisit this simplification using a 2D model which fully couples a linear elastic host rock with a pressurized chamber and a fluid-filled dike, assuming the lubrication approximation for viscous flow. This model is solved using the finite element method (FEM). Ensuring that dike propagation is stable limits the dike-tip cavity pressure for realistic fracture toughness. We find that computed trajectories fall between the classical principal stress and Mériaux and Lister (2002) trajectories for given regional stress and chamber pressure conditions. This leads to deviatoric stress magnitude estimates that are 1 to 2 times the classical estimates, and 1/2 to 1/3 the Mériaux and Lister (2002) estimates. We also explore the consequences of chamber depressurization due to magma outflow during dike propagation. For a given melt compressibility, the resulting trajectories align more closely with those obtained from the classical model, compared to those obtained assuming a constant chamber pressure. At higher ratios of tectonic stress to chamber pressure, the trajectories are nearly identical. In both the constant pressure and depressurizing chamber cases, our results suggest that realistic magma pressure profiles within a dike lead to smaller estimated ratios of deviatoric stress to chamber pressure than found by Mériaux and Lister (2002). Future work should extend dike propagation models to three dimensions, and more thoroughly explore effects of magma compressibility.

A detailed study of past eruptive activity is crucial to understanding volcanic systems and associated hazards. We present a meticulous stratigraphic analysis, a comprehensive chronological reconstruction, thorough tephra mapping, and a detailed analysis of the interplay between primary and secondary volcanic processes of the post-900 AD activity of La Fossa caldera, including the two main systems of La Fossa volcano and Vulcanello cones (Vulcano Island, Italy). Our analyses demonstrate how the recent volcanic activity of La Fossa caldera is primarily characterized by effusive and Strombolian activity and Vulcanian eruptions, combined with sporadic sub-Plinian events and both impulsive and long-lasting phreatic explosions, all of which have the capacity to severely impact the entire northern sector of Vulcano island. We document a total of 30 eruptions, 25 from the La Fossa volcano and 5 from Vulcanello cones, consisting of ash to lapilli deposits and fields of ballistic bombs and blocks. Volcanic activity alternated with significant erosional phases and volcaniclastic re-sedimentation. Large-scale secondary erosion processes occur in response to the widespread deposition of fine-grained ash blankets, both onto the active cone of La Fossa and the watersheds conveying their waters into the La Fossa caldera. The continuous increase in ground height above sea level, particularly in the western sector of the caldera depression where key infrastructure is situated, is primarily attributed to long-term alluvial processes. We demonstrate how a specific methodological approach is key to the characterization and hazard assessment of low-to-high intensity volcanic activity, where tephra is emitted over long time periods and is intercalated with phases of erosion and re-sedimentation.

Volcanic islands are often subject to flank instability, resulting from a combination of magmatic intrusions along rift zones and gravitational spreading causing extensional faulting at the surface. Here, we study the Koaʻe fault system (KFS), located south of the summit caldera of Kīlauea volcano in Hawaiʻi, one of the most active volcanoes on Earth, prone to active faulting, episodic dike intrusions, and flank instability. Two rift zones and the KFS are major structures controlling volcanic flank instability and magma propagation. Although several magmatic intrusions occurred over the KFS, the link between these faults, two nearby rift zones and the flank instability, is still poorly studied. To better characterize the KFS and its structural linkage with the surrounding fault and rift zones, we performed a detailed structural analysis of the extensional fault system, coupled with a helicopter photogrammetric survey, covering part of the south flank of Kīlauea. We generated a high-resolution DEM (~ 8 cm) and orthomosaic (~ 4 cm) to map the fracture field in detail. We also collected ~ 1000 ground structural measurements of extensional fractures during our three field missions (2019, 2022, and 2023). We observed many small, interconnected grabens, monoclines, rollover structures, and en-echelon fractures that were in part previously undocumented. We estimate the cumulative displacement rate across the KFS during the last 600 ~ 700 years and found a decrease toward the west of the horizontal component from 2 to 6 cm per year, consistent with GNSS data. Integrating morphology observations, fault mapping, and kinematic measurements, we propose a new kinematic model of the upper part of the Kīlauea’s south flank, suggesting a clockwise rotation and a translation of a triangular wedge. This wedge is bordered by the extensional structures (ERZ, SWRZ, and the KFS), largely influenced by gravitational spreading. These findings illustrate a structural linkage between the two rift zones and the KFS, the latter being episodically affected by dike intrusions.

Unveiling buried volcanic systems has been made easier through the application of high-resolution geophysical datasets in recent times. This improves the elucidation of systems related to caldera formation and collapse. An early Cretaceous bimodal volcanic suite, the Bumbeni Complex, crops out in a limited region of northern KwaZulu-Natal, South Africa and is dominated by felsic ignimbrites and rhyolitic lavas. However, the extent and evolution of the complex has remained ambiguous as much of the sequence is buried beneath recent sedimentary cover. This study has identified five nested caldera systems forming a caldera complex ~ 20 km in diameter through high-resolution aeromagnetic and radiometric surveys. Individual calderas are resolved by prominent positive and negative anomalies ranging from − 200 to + 300 nT based on International Geomagnetic Reference Field (IGRF) corrected Reduced to Pole (RTP) data. Field evidence and borehole core data indicate that caldera formation was accompanied by voluminous ignimbrite deposition with both intra- and extra-caldera volcaniclastic facies developed. Anomaly D, which represents the only exposed caldera structure within the complex, provides insights into the intrusive and extrusive rock types including syenite and granitic ring dykes, and ignimbrite units, resolved in radiometric data. Geophysical interpretations allow for the construction of an approximate relative-time-sequenced evolutionary model for the complex. Susceptibility modelling of the complex has identified circumferential dykes forming the margins of the calderas with a possible magma reservoir developed at ~ 4 km depth. The identification of silicic caldera systems in this region of southern Africa may have causal affiliations to the initiation and propagation of Gondwana rifting along the emergent northern KwaZulu-Natal margin.

Changes from dyke to sill propagation in the shallow crust are often caused by dissimilar layer properties. However, most previous studies have not considered the influence of glacial loading and unloading on dyke and sill deflection processes. Here, we attempt to collectively explore mechanical (layer stiffness) and geometrical (dyke dip, layer thickness) realistic parameters subject to two different magma overpressure values (namely 5 MPa and 10 MPa) that promote dyke-sill transitions in both non-glacial and glacial settings. To do this, we use as a field example, the Stardalur laccolith: a multiple stacked-sill intrusion located in SW Iceland. The laccolith lies near the retreating Langjökull glacier and was emplaced at the contact between a stiff lava layer and a soft hyaloclastite layer. We initially model two different stratigraphic crustal segments (stratigraphy a and b) and perform sensitivity analyses to investigate the likely contact opening due to the Cook-Gordon debonding and delamination mechanism under different loading conditions: magma overpressure, regional horizontal extension, glacial vertical load and a thin elastic layer at the stratigraphic contact. Our results show that contact opening (delamination) occurs in both non-glacial and glacial settings when the dissimilar mechanical contact is weak (low shear and tensile stress, zero tensile strength). In non-glacial settings, stiff layers (e.g., lavas) concentrate more tensile stress than soft layers (e.g., hyaloclastites/breccia) but accommodate less total (x–y) displacement than the surrounding host rock (e.g., soft hyaloclastites) in the vicinity of a dyke tip. Yet, a thicker hyaloclastite layer in the stratigraphy, subject to higher magma overpressure (P_o = 10 MPa), may encourage dyke-sill transitions. Instead, in glacial domains, the stress conditions imposed by the variable vertical pressure of the ice cap result in higher tensile stress accumulation and displacement in stiff layers which they primarily control sill emplacement.

Abstract

Vulcano, one of the most touristic islands in the Aeolian archipelago (Sicily, Italy), has been the site of significant volcanic unrest started in 2021, which is still ongoing. Fortunately, the crisis peak occurred in winter, so the direct consequences on the population were moderate. However, the socio-psychological impact was relevant as people had recently emerged from the Covid pandemic.

Since the most recent eruption occurred in 1888–1890, Vulcano has been characterized by fumarolic activity at the crater and diffuse degassing from the ground in the surrounding areas, contributing to a perception of low risk by the inhabitants. For this reason, it has been difficult for civil protection authorities at different territorial levels to implement risk mitigation measures on the island. The Italian Civil Protection Department together with the other administrations involved managed the volcanic unrest on the island through a series of actions that are described in this data report, facing complex challenges, such as the gas hazard management in populated areas, and experimenting with new methodologies that can be exported to similar contexts in the future.

In 2014, the Pāhoa lava flow at Kīlauea, on the Island of Hawaiʻi (USA), entered a string of pre-existing meter-width ground cracks in the volcano’s East Rift Zone. The ground cracks transported lava below the surface in a direction discordant to the slope of the landscape. The cracks, which were 100s of meters long and 10s to 100s of meters deep, also widened by up to several meters as they filled, probably in part at the expense of adjacent cracks, which likely closed. Widening of the cracks caused shallow crustal blocks on the volcano’s flank to shift—this deformation was captured by a nearby GPS station and a borehole tiltmeter. The GPS station moved away from the cracks in response, while the tiltmeter showed tilting toward the cracks, consistent with opening. Noting that the lava-filled cracks act as top-fed dikes, we adapt existing theory for the thermo-rheological evolution of dikes to analyze transport of lava captured by ground cracks and propose mechanisms for the exit of the lava back to the surface. This study shows that ground cracks as narrow as 50 cm wide can facilitate the transport of advancing lava flows and can carry lava in directions that differ from those expected based on surface topography, invalidating flow path projections based on the assumption of subaerial flow.

Mt. Etna, in Italy, is one of the most active volcanoes in the world, producing several explosive events in recent years. Those eruptions form high eruption columns that often reach the top of the troposphere (and sometimes even the lower part of the stratosphere) and create several disruptions to air traffic, mainly to the Fontanarossa International Airport in Catania, which is about 20 NM (~ 37 km; NM = Nautical Miles) away from the summit craters and is located in the main wind direction. In Italy, the institution responsible for volcano monitoring is the Istituto Nazionale di Geofisica e Vulcanologia (INGV). In 2007, the INGV, Osservatorio Etneo (INGV-OE) in Catania was appointed as “State Volcano Observatory” (SVO) and, in 2014, sent the first Volcano Observatory Notice for Aviation (VONA) message. Since that moment, several VONA messages have been sent, mainly due to the high frequency of Etna activity. In order to facilitate and speed in the generation and the dispatch of the VONA messages, a computer-assisted procedure has been designed and built to help the work done by the volcanologist on duty and by the two shift workers of the 24/7 Control Room of INGV-OE. Consequently, information on the explosive activity can be quickly provided to the Volcanic Ash Advisory Center (VAAC) in Toulouse and national air traffic offices, reducing risks to aviation operations. In this work, we describe how the computer-assisted procedure works, addressing the main advantages and possible improvements. We retain that a similar approach could be easily applied to other volcano observatories worldwide.