Eruptive History Research Articles

Decoding the state of stress and fluid pathways along the Andean Southern Volcanic Zone

Decoding means decrypting a hidden message. Here, the encrypted messages are the state of stress, fluid pathways, and volcano tectonic processes occurring in volcanoes of the Andean Southern Volcanic Zone (SVZ). To decode these messages, we use earthquake focal mechanisms, fault slip data, and a Monte Carlo simulation that predicts potential pathways for magmatic and hydrothermal fluids. From this analysis, we propose that SVZ volcanoes have three end-member stress patterns: (i) Stress-A, a strike-slip regime coupled with the regional far-field tectonic stress; (ii) Stress-B, an extensional regime that may be promoted by volcanic edifice loading and upward pressure due to magma inflation occurring within the upper brittle-crust; and (iii) Stress-C, a local and transient fluid-driven stress rotated ~90 degrees from Stress-A. Notoriously, Stress-C pattern was observed in most volcanoes with historical eruptions. We propose that volcanoes presenting Stress-B are attractive geothermal targets, while Stress-C could be used as a predicting signal for impending eruptions.

Paleomagnetism and age of the Leucite Hills Volcanic complex, Wyoming: Implications for eruptive history, landscape evolution, and the geomagnetic instability timescale (GITS)

The Leucite Hills Volcanic Field, southwest Wyoming comprises two dozen volcanic features including necks, flows, dikes, and plugs. It has been the focus of many petrologic studies as its volcanic and shallow intrusive rocks are one of the only surficial manifestations of ultrapotassic lamproite. We build on paleomagnetic findings of Sheriff and Shive (1980) by providing further paleomagnetic data from the Boars Tusk dike and Black Rock flows. We also characterize the magnetic mineral assemblage of these lamproites. Principal component analysis of alternating field (AF) and thermal demagnetization data indicate that the dike and breccias of Boars Tusk record a reversed magnetic polarity and the Black Rock lava records a normal polarity, both consistent with previous findings. This recording is typically carried by minerals with coercivities >15 mT and susceptibility measurements indicate magnetite, maghemite, and titanomagnetite as likely magnetic carriers. AF and thermal demagnetization experiments evince secondary magnetizations held by lower coercivity grains, likely caused by lightning strikes. 40Ar/39Ar incremental heating experiments from Boars Tusk and Black Rock give plateau ages of ∼2500 ka and ∼900 ka, respectively. Recent advances in the chronology of geomagnetic field reversals and excursions during the Quaternary permit integration of the Boars Tusk dike into the lower Matuyama chron, whereas the Black Rock lavas most probably record the Kamikatsura excursion. Notably, Black Rock records high inclinations that suggest the short-lived excursion achieved a full geomagnetic reversal, something not observed at other localities recording the Kamikatsura excursion. The Leucite Hills offer further opportunities to refine the Quaternary geomagnetic instability time scale (GITS), and to improve understanding of the eruptive and geomorphic evolution of this unusual volcanism.

Central Mediterranean tephrochronology for the time interval 250–315 ka derived from the Fucino sediment succession

In the lacustrine succession F4‐F5 of the Fucino Basin, central Italy, 20 visible tephra layers were identified in the time interval 250–315 ka (Marine Isotope Stages 8–9). Fifteen of them contained suitable material to explore their volcanic sources. Among these tephra some well‐known eruptions and eruptive sequences of the Roman and Roccamonfina volcanoes were identified, such as the Tufo Giallo di Sacrofano and the Lower White Trachytic Tuff, respectively. Furthermore, the sediment succession documents a more complex eruptive history of the Sabatini, Vulsini, Colli Albani and Roccamonfina volcanic complexes during the investigated period, as inferred from previously undescribed tephra deposits. Single‐crystal‐fusion 40Ar/39Ar dating of two of the inspected tephra layers combined with two already published tephra ages provided the basis for a Bayesian age‐depth model. The modelled tephra ages allow chronological constraining of so‐far undefined eruptions of the Sabatini (272.5±4.7, 281.8±4.7, 308.5±2.8, 312.8±2.1 ka), the Vulsini (311.7±2.3, 311.9±2.3 ka) and the Colli Albani (301.0±3.6 ka) volcanic districts. Two tephra layers of an undefined volcanic source from the Roman volcanoes have modelled ages of 309.5±2.7 and 310.5±2.6 ka. The new 40Ar/39Ar and modelled ages were further used for a reassessment of the timing of already known and dated eruptive units, such as the Tufo Giallo di Sacrofano (40Ar/39Ar: 289.3±4.8 ka). Tephra tentatively correlated with the Valle Santa Maria, Case Pisello and the White Trachytic Tuff Unit E3 or Unit F offer modelled ages for these eruptions of 296.6±3.9, 301.8±3.5 and 303.6±3.4 ka, respectively. The results complete the tephrostratigraphical investigations of the c. 425 ka old F4‐F5 record, extend the Mediterranean tephrostratigraphical framework and provide a significant contribution for improving knowledge on Italian volcanic explosive activity.

Volatiles, vesicles, and vugs: Unraveling the magmatic and eruptive histories of Steno crater basalts

AbstractIn 1972, Apollo 17 astronauts returned 170.4 kg of lunar material. Within 1 month of their return, a subset of those samples was specially curated with the forethought that future analytical techniques would offer new insight into the formation and evolution of the Moon. Of interest in this work is sample 71036, a basalt collected from the rim of Steno crater in the Taurus–Littrow Valley, which was stored frozen and was processed and released for study 50 years later. We report, for the first time, the detailed mineralogy and petrology of 71036 and its companion samples 71035, 71037, and 71055 using a novel combination of 2‐D and 3‐D methods. We investigate lunar volatiles through in situ measurements of apatite and 3‐D measurements of vesicles to understand the degassing histories of the Steno crater basalts. Our coupled 2‐D petrography and 3‐D tomography data sets support a model of the Steno crater basalts crystallizing in the upper crust of a mare lava flow. Apatite F and OH chemistry and the late‐stage deformation of voids and formation of smaller vesicles provide evidence supporting coeval degassing of volatiles and crystallization of mesostasis apatite in Apollo 17 basalts. This work helps to close knowledge gaps surrounding the origin, magmatic evolution, emplacement, and crystallization history of high‐titanium basalts.

Fragmentation behavior of young pyroclasts from Mt. Pelée, Martinique

The stratovolcano Mt. Pelée, Martinique, exhibits eruptive styles ranging from dome formation to sustained, highly violent explosive activity. Historical eruptions have produced lava domes and pyroclastic density currents, collectively termed Peléan activity. In pre-colonial times, several Plinian eruptions took place. Here, we explore physical controls on the proportions of fine particles produced—i.e., the fragmentation efficiency—during primary fragmentation. Samples were collected from ignimbrites from the 1929–1932 and 1902–1905 Peléan eruptions and the P1 (1300 CE), P2 (280 CE), and P3 (79 CE) Plinian eruptions. All samples are andesitic in bulk composition and contain a rhyolitic groundmass glass. The Peléan materials are more crystalline and less porous than their Plinian counterparts, a consequence of more extensive outgassing during dome formation. Representative blocks were cored and experimentally fragmented following rapid decompression (> 1 GPa·s−1 from initial pressure between 5 and 20 MPa). Dry sieving allowed for determining grain size distributions, from which the fractal dimensions, Df, were calculated as a quantification of fragmentation efficiency. Our results indicate different behaviors for Peléan and Plinian samples. While fragmentation efficiency is positively correlated with applied potential energy for Peléan samples, this relationship is not observed for the Plinian samples, possibly due to syn-fragmentation gas escape above a certain porosity. The rapid decompression experiments were designed to minimize secondary fragmentation by shear along the walls or impact while preserving the entirety of produced materials. Thus, our experimental grainsize data are physically linked to sample textures and overpressure. By comparison with natural pyroclastic products—commonly incompletely preserved—we can approach quantitatively constraining the energetic conditions underlying individual eruptions.

A case of catamenial erythema multiforme major successfully treated with goserelin.

We report a case of catamenial erythema multiforme major in a 46-year-old female. She was treated successfully with goserelin, a GnRH agonist, until the expected age of menopause; however, its therapeutic effects persisted for longer than expected, possibly due to accumulation in adipose tissue. A group of menstrual cycle-related dermatoses and hypersensitivity syndromes exist but are rarely reported in the literature. A history of recurrent cutaneous eruptions in premenopausal females should be considered in the context of the menstrual cycle. The diagnosis of menstrual cycle-related dermatoses is largely clinical, although provocation testing can assist. Treatment options are broad and are aimed at reducing the immune response and/or suppressing ovulation. Goserelin may accumulate and have a gonadotrophin-suppressing effect for longer than expected.

Geomorphological Processes in the Central Kamchatka Depression (the Kamchatka Peninsula, Ne Pacific) During the Last 30 Ka

The paper presents a reconstruction of geomorphological processes in the Central Kamchatka Depression (CKD) since 30 ka, including the global LGM time. Major geomorphological processes of this period included the evolution of volcanic edifices accompanied by steady tectonic submergence. Glaciers that originated from volcanic edifices were greatly affected by both climatic forcing and the eruptive history of their host volcanoes.
 The most prominent geomorphological feature of the studied time was a giant paleolake filled the CKD. The reassessed extent and timing of glaciation and volcanism provided the possible lake fill and discharge model due to the evolution of a piedmont glacier originating from the Old Shiveluch Volcano edifice. The lake discharge likely was gradual and started some 19 ka during the cold settings of LGM, and therefore did not have a climatic origin. The most possible trigger of the discharge is the change in ice supply from the highly active Shiveluch Volcano due to large sector collapses. During the Holocene, the ongoing tectonic submergence of the CKD have been preventing the complete drainage of this paleolake. Even now, an enormously wide floodplain of the Kamchatka River hosts a lacustrine system with a total area of water surface comparable to the largest lakes of the peninsula.

Insights into the explosive eruption history of the Campanian volcanoes prior to the Campanian Ignimbrite eruption

The Campanian Volcanic Zone (CVZ) comprises multiple active volcanoes and includes the highly productive Campi Flegrei and Ischia caldera systems. These caldera volcanoes have produced probably the largest eruptions in Europe in the past 200 ka, such as the Monte Epomeo Green Tuff (MEGT; Ischia) at ca. 56 ka and the Campanian Ignimbrite (CI; Campi Flegrei) at ca. 40 ka, which form widespread isochrons across the Mediterranean region. These closely-spaced volcanic centres erupt phonolitic to trachytic glass compositions that are similar, and thus it can be challenging to correlate tephra deposits to specific volcanic sources. Here we present a detailed tephrostratigraphy for pre-CI eruption activity using the units preserved within a sequence at the coastal Acquamorta outcrop, on the western side of the CI caldera rim. Both the MEGT and CI units are present in the section, and they bracket twelve eruption units that were logged and sampled. New major and trace element glass chemistry data have been acquired for these Acquamorta tephra deposits. Three eruption deposits from Ischia and nine from Campi Flegrei are identified, which helps constrain the tempo of volcanic activity of these centres between the large caldera-forming eruptions. The three Ischia tephra deposits between the MEGT and the CI are indistinguishable based on both major and trace element glass chemistry and cannot be correlated to a specific or known eruption in this interval, such as the Schiappone tephra. The compositional variations between the Campi Flegrei eruptions reveal temporal shifts in the composition of the tephra deposits that reflect changes in the magmatic system prior to the CI eruption. These deposits indicate that there were at least nine eruptions at Campi Flegrei within 16 ka of the enormous CI eruption, and suggest that there was no significant period of repose before the caldera generating eruption.

Magma plumbing architectures and timescales of magmatic processes during historical magmatism on the Reykjanes Peninsula, Iceland

In the past 4000 years, three rifting episodes have occurred on the Reykjanes Peninsula (RP, SW Iceland) at time intervals of about 800-1000 years, with the activation of four of the five volcanic systems on the peninsula: Reykjanes, Svartsengi, Krýsuvík and Brennisteinsfjöll. In 2021 AD, 2022 AD and 2023 AD, three eruptions occurred in the Fagradalsfjall volcanic system, the only volcanic system that remained inactive during these past rifting episodes. Considering the eruptive history of the peninsula, this could mark the onset of a new eruptive episode. Although extensive petrochemical datasets have emerged from past rifting episodes, little is known about magma plumbing configuration and timescales of pre-eruptive magmatic processes. In this work, we focus on 16 basaltic lava units erupted across RP during a well-established rifting episode: the 800-1240 AD Fires. We analysed major and minor element contents of glasses, mineral phases and melt inclusions, and we reconstruct plumbing system architecture and constrain mixing-to-eruption timescales, with the goal of assessing likely eruption scenarios of a possible future eruptive episode. Mineral-melt equilibria suggests that most of crystal cores are antecrysts that did not crystallize from the magmas that carried them to the surface, but instead were scavenged from disaggregating mush layers genetically related to the erupted magmas. Magmas erupted in the easternmost part of the RP reveal larger contributions from geochemically enriched mantle-derived melts. However, MIs that record various extents of mixing of geochemically enriched and depleted components throughout the entire peninsula appear devoid of any spatial control of the underlying mantle. Independent clinopyroxene-melt and melt-based barometry, after correction for microlite crystallization, show consistent results and suggest that magmas from the western part of the peninsula were extracted from reservoirs located at about 7-10 km depth. In contrast, and similar to observations from recent eruptions at Fagradalsfjall, the easternmost system, Brennisteinsfjöll, was fed from deeper crustal reservoirs, at about 14-21 km depth. Fe-Mg diffusion chronometry applied to olivine rims suggests short mixing-to-eruption timescales on the order of days to weeks and likely faster ascent rates of magmas underneath Brennisteinsfjöll. Compared to 2021 AD Fagradalsfjall, mixing-to-eruption timescales were considerably shorter during the 800-1240 AD Fires. With inferred eruption durations on the order of months, the short olivine rim diffusion records are consistent with several discrete eruptive phases, which eventually assembled the individual magmatic units. In the light of possible future eruptive episodes on the RP, our work suggests that magmas are likely to accumulate at persistent depths across the RP, with key implication for interpreting pre-eruptive signals and eruption mitigation.

The diversity of volcanic hazard maps around the world: insights from map makers

The IAVCEI Working Group on Hazard Mapping has been active since 2014 and has facilitated several activities to enable sharing of experiences of how volcanic hazard maps are developed and used around the world. One key activity was a global survey of 90 map makers and practitioners to collect data about official, published volcanic hazard maps and how they were developed. The survey asked questions about map content, design, and input data, as well as about the map development process and key lessons learned. Here we present the results of this global survey, which are then used to quantitatively describe and summarise current practices in volcanic hazard map development.We received entries related to 89 volcanic hazard maps (78% long-term/background maps and 22% short-term/crisis hazard maps), covering a total of 80 volcanoes across 28 countries. Although most maps captured in the survey are volcano-scale maps of stratovolcanoes that show similar types of content, such as primary hazard footprints or zones, they vary greatly in input data, communication style, format, appearance, scale, content, and visual design. This diversity stems from a range of factors, including differences in map purpose, the methodology used, the level of understanding of past eruptive history, the prevailing scientific and cartographic practice at the time, the state of volcanic activity, and variations in culture, national map standards and legal requirements.Experiences and lessons shared by our respondents can be divided into six main themes: map design considerations; the process of map development; map audience and map user needs; hazard assessment approach; map availability and accessibility; and external (e.g., political) influences. Insights shared included the importance of: visual design elements, map testing and evaluation, working with stakeholders and end users to improve a map’s efficacy and relevance, and considering possible unanticipated uses of hazard maps. These free-form text insights (i.e., responses to open-ended questions) from map makers and practitioners familiar with the maps lend depth and clarity to our results. They provide a rich complement to our more quantitative analysis of design elements and of approaches used to determine and delineate map zones.Results from our global survey of hazard map makers and practitioners, together with insights from other key initiatives of the Working Group on Hazard Mapping such as the Volcanic Hazard Maps Database (VHMD; https://volcanichazardmaps.org/), provide a snapshot of the wide variety of volcanic hazard maps generated over the past decades, and improve our understanding of the diversity across volcanic hazard mapping practices. These initiatives represent important steps towards fulfilling the aims of the Working Group, namely, to construct a framework for a classification scheme for volcanic hazard maps and to promote harmonized terminology, as well as to identify and categorise good practices and considerations for volcanic hazard mapping.

Syn‐Rift Magmatism and Sequential Melting of Fertile Lithologies in the Lithosphere and Asthenosphere

AbstractThe timing and rate of decompression melting of a compositionally heterogeneous mantle during continental rifting are assessed with a new one‐dimensional geodynamic code, MELT1D. MELT1D computes pressure and temperature in the extending lithosphere and rising asthenosphere and calculates the resulting melt fraction and eruption rates for different lithologies. A series of models simulate syn‐rift melt production from (a) dry and wet depleted lherzolite similar to the mantle that underlies most mid‐ocean ridges, (b) dry and wet relatively fertile ultramafic compositions representing plume or primitive mantle material, (c) pyroxenite representing recycled ultramafic oceanic crust or magmatic metasomes, and (d) basalt representing recycled mafic crust or metasomes. The models predict sequential melting of the different compositions that is broadly consistent with basalt eruption histories in many Phanerozoic rifts. Results show a progressive transition in magma sources as the lithosphere thins, beginning with melting of wet mantle and compositionally fertile mafic components near the lithosphere‐asthenosphere boundary during the earliest stages of extension. This transitions to magmatism dominated by melting of relatively fertile ultramafic components (pyrolitic and pyroxenitic compositions) as extension progresses, and finally to melting of ambient lherzolite asthenosphere as lithosphere thinning approaches breakup. Mantle composition, pre‐rift lithosphere thickness, and mantle temperature exert the greatest controls on the timing and volumes of magmas produced from each lithology. In general, a cool or thick lithosphere has a greater capacity to sequester fertile lithologies than thin or warm lithosphere, and thus has a greater capacity to produce early syn‐rift magmas without requiring a hot mantle plume.

Constraining the eruption history of Rangitoto volcano, New Zealand, using palaeomagnetic data

Constraining the eruption history of Rangitoto volcano, New Zealand, using palaeomagnetic data

Volcanology and facies analysis of the youngest phreatomagmatic deposits on O'ahu, Hawai'i

The area known as the Lānaʻi Lookout has Oʻahu's youngest and best exposures of deposits from pyroclastic density currents (PDCs), generated by explosions involving magma-water interaction. This work presents the first detailed facies analysis of the deposits at the Lānaʻi Lookout, fundamental to understanding the explosion dynamics, post-fragmentation transport and depositional processes, and to unravel the eruptive history. The lithofacies identified include planar-bedded, low-angle, and megaripple, cross-bedded ash to lapilli, accretionary lapilli-rich falls and isolated ballistic blocks and bombs. These features are interpreted as generated by mostly dilute PDCs, co-PDC fall and sedimentation from eruptive clouds and ballistic-charged jets. Overall, at least four eruptive stages formed the pyroclastic succession: (i) frequent, brief explosions from Kahauloa and Koko craters, producing fallout deposits and ballistics; (ii) a dominant stage of sustained passing to short-lived production of PDCs from Kahauloa crater, followed by a short break in volcanic activity; (iii) return of explosive activity dominated by fallout deposits likely sourced at Kahauloa; (iv) intermittent PDCs from Kahauloa alternating with debris flows coming down Koko Crater flanks. This stage is followed by lava flow emplacement that marked the end of the explosive eruptions at the Koko Rift system. In summary, the lithofacies analysis and stratigraphic relations of this complex multi-vent system informs on the dynamics, eruptive style, and frequency of eruptions of the late-stage volcanism on Oʻahu.

Frontiers of thermobarometry: GAIA, a novel Deep Learning-based tool for volcano plumbing systems

The anatomy of the plumbing system of active volcanoes is fundamental to understand how magma is stored and channeled to the surface. Reliable geothermobarometric estimates are, therefore, critical to assess the depths and temperatures of the complex system of magmatic reservoirs that form a volcano apparatus. Here, we developed a novel Machine Learning approach (named GAIA, Geo Artificial Intelligence thermobArometry) based upon Feedforward Neural Networks to estimate P-T conditions of magma (clinopyroxene) storage and migration within the crust. Our Feedforward Neural Network method applied to clinopyroxene compositions yields better uncertainties (Root-Mean-Square Error and R2 score) than previous Machine Learning methods and set the basis for a novel generation of reliable geothermobarometers, which extends beyond the paradigm associated to crystal-liquid equilibrium. Also, the bootstrap procedure, inherent to the Feedforward Neural Network architecture, permits to perform a rigorous assessment of the P-T uncertainty associated to each clinopyroxene composition, as opposed to the Root-Mean-Square Error representing the P-T uncertainty of whole set of clinopyroxene compositions.As a test, we applied GAIA to assess P-T conditions of five Italian volcanoes (Somma-Vesuvius, Campi Flegrei, Etna, Stromboli, Volcano), which are among the most dangerous volcanic centres in Europe. The results on the depths of the plumbing systems are in excellent agreement with those obtained with independent geophysical and geodetic surveys, and provide further evidence to current models of volcano plumbing systems consisting of physically-separated reservoirs interconnected by a network of conduits channelling magma en route to the surface. The results on the magma (clinopyroxene crystallization) temperatures are also in agreement with other estimates, albeit obtained considering - mainly but not only - thermodynamically-based clinopyroxene-liquid geothermometers.GAIA can set robust estimates of magma storage, segregation, and ascent conditions within the plumbing system of active volcanoes, helping to unravel P-T variations, if any, during their eruptive history and providing robust clues to volcanic hazard assessment.

The cenozoic marine tephra record in Indian Ocean deep drill sites

Provenance studies of widely distributed tephra deposits are important to deduce systematic changes in the source, size, distribution, and temporal variation of regional explosive volcanism. Long-term deep ocean drilling sedimentary records are particularly useful for these kind of studies. In this study, we establish a robust tephrochronostratigraphy for 235 primary marine tephra layers collected during International Ocean Discovery Program Expeditions 353, 354, and 362, complemented by older drill cores from Deep Sea Drilling Program and Ocean Drilling Program Legs 22, 119, 120, 121, and 183. We infer at least two major phases of highly explosive arc volcanism during the Early Miocene to Pleistocene, as well as three episodes related to explosive ocean island volcanism located in the Kerguelen plateau, the Broken Ridge, and close to Réunion reaching back to the Paleogene.Twenty-two widespread arc-derived tephra layers from individual eruptions can be correlated by geochemical fingerprinting between multiple holes. These provide nine Quaternary and 13 Neogene temporal tie points in the sedimentary sequence including four new UPb zircon ages. Provenance analysis of the marine tephra layers, which is based on glass composition, assign eleven of these layers to a Toba-like source, ranging from 24 Ma to 75 ka, with the youngest correlative being Young Toba Tuff. Based on distribution pattern, thickness decay, and compositional evidence another eleven tephra layers can be assigned to a northern Sumatran Arc or to an Andaman Arc provenance. First-order minimum eruptive volume estimates for the Neogene tephra layers imply eruptive magnitudes ranging from M = 6.5 to M = 7.5, proving a continuous history of large explosive eruptions from the Sumatran/Andaman Arc since the Neogene, as previously known from the Quaternary. Plain language summaryKnowing the origin of large volcanic eruptions is important to deduce systematic changes in the source, size, distribution, and changes of regional explosive volcanism. In this study we use widely dispersed marine volcanic deposits in the Indian Ocean, so-called marine tephra layers, to reconstruct the history of a) Sumatran highly explosive eruptions over the last 24 Ma, and b) ocean island volcanism frequently observed in the Indian Ocean. The marine deposits are often the only evidence of major eruptions in the past because respective volcanic edifices and terrestrial deposits are often destroyed by subsequent eruptions, eroded or overlain by younger deposits. Deep ocean drilling provides the unique possibility to overcome these problems by recovering long, tephra-bearing marine sediment sequences in the drill cores. We present the results for 235 primary marine tephra layers that have been collected during eight deep drilling campaigns in the Indian Ocean. Twenty-two widespread connections of arc-derived tephra layers are established by comparing distinctive geochemical fingerprints of the tephras between multiple locations. These provide nine Quaternary and 13 Neogene temporal tie points in the sedimentary sequence. The origin of these marine tephra layers is determined based on the unique glass compositions of individual volcanoes and eruptions, assigning 11 of these layers to a Toba-Caldera-like source ranging from 24 Ma to 75 ka, with the youngest correlative being the iconic Young Toba Tuff. Another eleven tephra layers can be assigned to a northern Sumatran Arc or to an Andaman Arc provenance.Our record demonstrates a continuous history of large explosive eruptions from the Sumatran/Andaman Arc since the Neogene. We additionally infer (1) at least two major phases of highly explosive arc volcanism from the Sumatra-Andamen volcanic chain during Early Miocene to Pleistocene times, and (2) three episodes related to explosive ocean island volcanism found in the Kerguelen plateau, the Broken Ridge, and close to Réunion.

Marine records reveal multiple phases of Toba’s last volcanic activity

The Indonesian Young Toba Tuff (YTT), classically dated around 74 ka BP, is considered as a short-lived explosive cataclysmic super-eruption. The huge amounts of ash and SO2 emitted are likely to have triggered a volcanic winter which accelerated the transition to the last glaciation, and may have induced a human genetic bottleneck. However, the global climatic impact of the YTT or its duration are hotly debated. The present work offers a new interpretation of the Toba volcanic complex eruptive history. Analysing the BAR94-25 marine core proximal to the Toba volcanic center and combining it with high-resolution tephrostratigraphy and δ18O stratigraphy, we show that the Toba complex produced a volcanic succession that consists of at least 17 distinct layers of tephra and cryptotephra. Textural and geochemical analyses show that the tephra layers can be divided in 3 main successive volcanic activity phases (VAP1 to VAP3) over a period of ~ 50 kyr. The main volcanic activity phase, VAP2, including the YTT, is likely composed of 6 eruptive events in an interval whose total duration is ~ 10 ka. Thus, we suggest that the eruptive model of the Toba volcano must be revised as the duration of the Toba volcanic activity was much longer than suggested by previous studies. The implications of re-estimating the emission rate and the dispersion of ashes and SO2 include global environmental reconstitutions, climate change modelling and possibly human migration and evolution.

Unsuspected explosive activity of Montagne Pelée (Lesser Antilles) during the 25–10 ka period

The recent eruptive history of Montagne Pelée volcano was dominated by a period of vigorous basaltic andesitic magma production (36−25 ka) followed by a long period of lower activity (i.e., with less frequent and less voluminous eruptions) and a renewal of felsic magma production in the last 10 ka. The temporal succession of volcanic events that occurred during the 25−10 ka period and the timing of felsic magma production are currently poorly constrained. This study focuses on the stratigraphy and eruptive dynamics of the pyroclastic deposits emplaced immediately after 25 ka. New on-land stratigraphic correlations and radiocarbon dating measurements allow us identifying six major explosive eruptions. We use field data on tephra dispersal, thickness and grain-size distribution together with physical models of explosive volcanic plumes to estimate the eruption source parameters. Our results show that these events are VEI 4 eruptions with intermediate magnitudes (from M = 4.2 to M = 5.1) and intensities (from I = 10.6 to I = 11.6). These eruptions share several characteristics with the most recent Plinian eruptions of Montagne Pelée volcano (i.e., mass eruption rate, maximum column height, runout of pyroclastic density currents, glass composition). The tephra succession documents two phases of magma production rates. The first phase from 25 to 14 ka corresponds to a period of low activity with a magma production rate of 0.04 km3 kyr−1. The second phase from 14 to 10 ka is characterized by a significant increase of the volcanic activity with a magma production rate of 0.4 km3 kyr−1, consistent with previous estimates.

Inner structure of monogenetic Pilot Knob submarine volcano (Austin, Texas) revealed by electrical resistivity tomography and magnetic surveys

Pilot Knob is the eroded and exposed core of an extinct subaqueous to emergent volcano that formed in a shallow Late Cretaceous epicontinental sea in the ancient Gulf of Mexico during the deposition of Austin Chalk Limestone. With the aim of understanding the inner structure of this volcano, we have conducted geophysical surveys (resistivity and magnetometry) to provide an insight into the past eruptive history. High-resolution electrical resistivity and magnetic data reveal, for the first time, a buried tuff mound, an explosion crater, several dikes and vents, basaltic flows, and limestone blocks within the volcano. A combination of geologic and geophysical data suggests that Pilot Knob volcano started with an explosion as a maar-type volcano beneath a shallow sea floor. Then, it likely has evolved into a tuff mound-type volcano with “Surtseyan” eruptions, before finally evolving into an emergent volcanic center. Major resistivity and magnetic anomalies align approximately in the east–west and north–south directions, respectively. Such alignments suggest that Pilot Knob is situated on east–west and north–south fractures, along which its most significant volcanic activity occurred. Results also provide valuable information in delineating tuff mounds and their structural characteristics.

DP14 Going against the grain: eosinophilic dermatosis presenting as erythema gyratum repens

Abstract Erythema gyratum repens (EGR) is a rare, paraneoplastic rash with a characteristic woodgrain appearance. It is heavily associated with malignancies, including lung, oesophageal and breast cancers. However, other conditions can mimic EGR, including leucocytoclastic vasculitis, immunobullous and papulosquamous conditions. We report an unusual presentation of eosinophilic dermatosis with an EGR-like pattern, not associated with malignancy. A 67-year-old woman presented with a 2-week history of a pruritic eruption on her legs. It initially started with three small circular erythematous macules on the right leg and one on the left leg. Over the course of a few days, the three macules evolved into large concentric annular patches simulating woodgrain, which raised the clinical suspicion of EGR. After a week, the patches began to blister with accentuation of some of the blisters on the edge of the annular patches. She denied any previous history of skin problems or changes in medication and was otherwise well with no systemic symptoms, including fever. In view of the almost 70% chance of an underlying malignancy, she was thoroughly investigated. Her full blood count, eosinophil count, liver function test, renal profile and serum C3 and C4 were normal. Skin basement membrane/desmosome antibodies and Borrelia burgdorferi IgG and IgM antibodies were also negative. Histology revealed prominent epidermal spongiosis with some corneal and intraepidermal vesicles that were cell-poor and contained only red blood cells. The underlying dermis showed prominent papillary dermal oedema with a brisk interstitial and superficial/deep perivascular mixed inflammatory infiltrate containing numerous eosinophils but no obvious flame figures. There was also eosinophil infiltration into the underlying subcutaneous fat. Direct immunofluorescence was negative. The histological pattern was that of an eosinophil-rich dermatitis with vesiculation; the history and morphology of the eruption were not compatible with bullous insect bites. An eosinophilic dermatosis such as eosinophilic cellulitis presenting with an EGR-like pattern was considered to be the most likely possibility for her presentation. Computed tomography of the neck, thorax, abdomen and pelvis, bidirectional endoscopy and mammography revealed no malignancies. She was treated with prednisolone 30 mg daily for 10 days with Elocon® ointment, and the eruption improved remarkably leaving postinflammatory colour changes that subsequently resolved. We would like to raise the awareness that an EGR-like pattern can be found in several other dermatoses, including eosinophilic dermatosis, and woodgrain pattern is not always equivalent to EGR or a high risk of associated malignancies (Table 1).Table 1Erythema gyratum repens-like dermatosesLeucocytoclastic vasculitisImmunobullousPapulosquamousBullous pemphigoidPsoriasisEpidermolysis bullosa acquisitaPityriasis rubra pilarisLinear IgA dermatoses

DP10 A relapsing–remitting rash with associated neurological symptoms: a rare presentation of ​­neuro-Sweet syndrome

Abstract A 46-year-old woman presented with an 8-week history of an asymptomatic eruption on her upper extremities and back. She had a history of ulcerative colitis, asthma and hyposplenism. There had been no changes to her regular medications. Over the next 3 years, she developed a relapsing and remitting course of headaches, pyrexia and feeling unwell with the associated rash. She further developed deafness and vertigo and was admitted with headaches, blurred vision and paraesthesia of the fingers. Physical examination revealed multiple erythematous, asymptomatic, annular plaques present on her upper extremities and back with no oral, genital or ophthalmological lesions. Skin biopsy from the lesion on the upper back showed a neutrophilic dermatosis with mildly acanthotic epidermis, superficial dermal collection of acute inflammatory cells, dermal oedema and endothelial swelling, with no evidence of vasculitis. This was considered in keeping with Sweet syndrome. Magnetic resonance imaging of the brain revealed meningoencephalitis and focal cerebritis. A lumbar puncture performed for infection was negative. Following this, a diagnosis of neuro-Sweet syndrome (NSS) was made. She has responded well to oral steroids and is currently well controlled on dapsone. To date, extensive malignancy screens have been negative. Sweet syndrome, or acute febrile neutrophilic dermatosis, is characterized by fever, malaise, leucocytosis and painful distinctive skin lesions and may be associated with malignancies, drugs and infection. Skin biopsy shows dense dermal infiltration of neutrophils without any histological signs of vasculitis. Sweet syndrome is known to involve multiple organs; however, involvement of the central nervous system (CNS) is rare. When the CNS is involved, it is referred to as NSS and is defined as the coexistence of characteristic skin lesions of Sweet syndrome with encephalitis or meningitis (Suh HB, Kim HJ. Recurrent neuro-Sweet disease associated with preceding upper respiratory infection: a case study. iMRI 2018; 22:187–93). Although the condition is usually steroid responsive, disease recurrences have been reported in 50% of cases in the literature (Hisanaga K, Iwasaki Y, Itoyama Y, Neuro-Sweet Study Group. Neuro-Sweet disease: clinical manifestations and criteria for diagnosis. Neurology 2005; 64:1756–61). It is important to note that the clinical features and imaging results in NSS are similar to those of neuro-Behçet disease (NBD), and it is important to distinguish between the two as CNS involvement in NSS is often transient, whereas NBD often follows a more progressive course. We report a rare case of NSS and highlight that NSS should be considered by dermatologists in patients presenting with recurrent skin lesions of Sweet syndrome and associated neurological symptoms.