1,720,991 research outputs found
What do we know about calderas? The 2012 IAVCEI Commission on Collapse Calderas Workshop in Bolsena, Italy.
No full text
From structure- to erosion-controlled subsiding calderas: evidence thresholds and mechanics
No full textKinematic analysis of vertical collapse on volcanoes using experimental models time series
No full textDynamic feeder dyke systems in basaltic volcanoes
No full textIn this paper, we describe the 1809 eruption of Mt. Etna, Italy, which represents one historical rare case in which it is possible to observe details of the internal structure of the feeder system. This is possible thanks to the presence of two large pit craters located in the middle of the eruptive fracture field that allow studying a section of the shallow feeder system. Along the walls of one of these craters, we analysed well-exposed cross sections of the uppermost 15–20 m of the feeder system and related volcanic products. Here, we describe the structure, morphology and lithology of this portion of the 1809 feeder system, including the host rock which conditioned the propagation of the dyke, and compare the results with other recent eruptions. Finally, we propose the dynamic model of the magma behaviour inside a laterally-propagating feeder dyke, demonstrating how this dynamic triggered important changes in the eruptive style (from effusive/Strombolian to phreatomagmatic) during the same eruption. Our results are also useful for hazard assessment related to the development of flank eruptions, potentially the most hazardous type of eruption from basaltic volcanoes in densely urbanized areas, such as Mt. Etna.Published1-112T. Tettonica attiva2V. Dinamiche di unrest e scenari pre-eruttivi3V. Dinamiche e scenari eruttivi4V. Vulcani e ambiente6A. Monitoraggio ambientale, sicurezza e territorioN/A or not JCRope
The 1914 Taisho eruption of Sakurajima volcano: stratigraphy and dynamics of the largest explosive event in Japan during the twentieth century
Full text linkThe 1914 Taisho eruption of Sakurijima volcano was Japan’s highest intensity and magnitude eruption of the twentieth century. After a 35-year period of quiescence, the volcano suddenly rewoke a few days before the eruption, when earthquakes began to be felt on Sakurajima Island. The eruption began on January 12, 1914, from two fissures located on opposite sides of the volcano, and was characterized by a complex time evolution and changes in eruptive styles. The eruption began with a subPlinian explosive phase in which two convective columns rose from the two fissures. Both plumes were sustained for at least 2 days. This resulted in deposition of a widely dispersed tephra sequence. After this phase, the eruption evolved to a final, waning phase, shifting toward effusive activity that lasted until April 1914. During the first weeks, effusive activity was also accompanied by ash emission. The complex sequence of events, characterized by contemporaneous explosive and effusive activity, is typical of several recently observed mid-intensity eruptions, such as during the 2011 eruption of Cordón Caulle, Chile. The stratigraphic sequence of the eruptive deposits from the Taisho eruption comprises alternating coarse-to-fine lapilli beds with ash beds dispersed toward the ESE and SE. These deposits can be subdivided into three lapilli-bearing units (Units T1, T2 and T3, which correspond to the subPlinian phase) and one ash-bearing unit (Unit T4, which corresponds to the final ash venting, accompanying the first day/weeks of lava flow activity). Grain size analyses from each unit reveal a marked polymodal distribution generally described by the sum of two or three Gaussian subpopulations. Both the modes and the relative amounts of the coarse subpopulations vary with distance from vent, with those of the fine subpopulation remaining nearly constant. Within the vertical sequence, component analysis shows a progressive increase in lithic fragments, suggesting that conduit enlargement continued until the final stages of the eruption. The estimated volume of the tephra deposit of the subPlinian phase of the eruption is 0.33 ± 0.11 km3 (dense rock equivalent (DRE) volume = 0.09 ± 0.03 km3). The height of the eruption column was also assessed by using four different isopleth maps compiled based on different strategies for the characterization of the largest clasts. The maximum height attained by the eruption column is estimated at 15.0 ± 1.2 km above the vent, resulting in a maximum mass discharge rate of 3.6 ± 1.2 × 107 kg s−1 (calculated taking into account the strong effect of wind advection). Finally, different classification schemes were applied to classify the eruption, which generally straddles the fields between Plinian and subPlinian
Eruptive dynamics and fragmentation mechanisms during cyclic Vulcanian activity at Sakurajima volcano (Japan): Insights from ash texture analysis
Full text linkQuantitative morpho-textural analysis of volcanic ash is one of the most effective tools to characterize the style of ash-dominated volcanic activity, and to investigate the complex interplay between conduit processes and the associated eruptive dynamics. In this framework, many questions still remain unanswered about the role of conduit processes, particularly of the magma fragmentation processes, in controlling the eruptive dynamics of the unsteady and highly-transient Vulcanian explosions. For this reason, we analyzed ash samples collected during a five days-long eruptive sequence at Sakurajima volcano (Japan), to derive information about ash morphometry and textural features over the entire sequence. During the observed sequence, eruptive activity showed high unsteadiness in the modalities of ash emission, which included all the main different eruptive styles typical of the recent period of Sakurajima activity. Three main intra-eruptive phases (Phase1, Phase2 and Phase3) were recognized based on visual observations and thermal data. Quantitative information about external ash morphometry (i.e., shape) and internal textures were measured for the particles associated with the different phases and discussed in terms of the observed eruptive variability. We quantified crystallinity and vesicularity of ash grains, the crystal size distribution (CSD) of microlites and the microlite number density (MND) of the groundmass for a representative set of ash particles. We discussed the links between the eruptive dynamics and the dominant processes of magma fragmentation, as shown by the combination of the morpho-textural features of ash throughout the whole eruptive sequence and the observed variations of the eruptive phases. All the evidence presented in this work confirm the constant presence at Sakurajima of a highly stratified and degassed magma within the conduit, suggesting that the transient dynamics of the eruption were strongly controlled by variations in the process of magma fragmentation driving the eruptions during the different phases. In particular, the morpho-textural characteristics of ash suggest that Vulcanian eruptions at Sakurajima can be controlled by the progressive pressurization of the upper portion of the magma conduit (between 10 and 50 m in depth). Moreover, using crystal textures, we inferred that the time needed for conduit refilling during intra-eruptive stages is comprised between 1 and 10 month. The resulting information on the eruptive dynamics of Sakurajima is of primary importance for a more exhaustive comprehension of the low-to-mid intensity, ash-dominated explosive activities
Potential impacts of tephra fallout from a large-scale explosive eruption at Sakurajima volcano, Japan
Full text linkWe present an exposure analysis of infrastructure and lifeline to tephra fallout for a future large-scale explosive eruption of Sakurajima volcano. An eruption scenario is identified based on the field characterization of the last subplinian eruption at Sakurajima and a review of reports of the eruptions that occurred in the past six centuries. A scenario-based probabilistic hazard assessment is performed using the Tephra2 model, considering various eruption durations to reflect complex eruptive sequences of all considered reference eruptions. A quantitative exposure analysis of infrastructures and lifelines is presented primarily using open-access data. The post-event impact assessment of Magill et al. (Earth Planets Space 65: 677-698, 2013) after the 2011 VEI 2 eruption of Shinmoedake is used to discuss the vulnerability and the resilience of infrastructures during a future large eruption of Sakurajima. Results indicate a main eastward dispersal, with longer eruption durations increasing the probability of tephra accumulation in proximal areas and reducing it in distal areas. The exposure analysis reveals that 2300 km of road network, 18 km(2) of urban area, and 306 km(2) of agricultural land have a 50% probability of being affected by an accumulation of tephra of 1 kg/m(2). A simple qualitative exposure analysis suggests that the municipalities of Kagoshima, Kanoya, and Tarumizu are the most likely to suffer impacts. Finally, the 2011 VEI 2 eruption of Shinmoedake demonstrated that the already implemented mitigation strategies have increased resilience and improved recovery of affected infrastructures. Nevertheless, the extent to which these mitigation actions will perform during the VEI 4 eruption presented here is unclear and our hazard assessment points to possible damages on the Sakurajima peninsula and the neighboring municipality of Tarumizu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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