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Arsenate As(V) is a toxic contaminant commonly found in aquifers and groundwater that poses significant risks to human health. The effective treatment of arsenic-contaminated water is therefore crucial for safeguarding public health. This study investigates removing As(V) using iron oxide-coated ignimbrite in batch experiments by varying the adsorbent dosage, initial As(V) concentration, contact time, and system temperature. The adsorption experiments revealed that the Langmuir isotherm model better fit the data (R2 = 0.99) than the Freundlich model (R2 = 0.73). According to the Langmuir model, the maximum adsorption capacity of As(V) on the iron oxide-coated ignimbrite was 4.84 mg·g⁻1 ± 0.12 mg·g⁻1 of As(V), with a standard deviation of ±0.05 mg·g⁻1 after 2 h of exposure with 0.15 g/50 mL iron oxide-coated ignimbrite adsorbent concentration. In the kinetic analysis, the pseudo-first-order model best described the adsorption process at 283 K, 293 K, and 303 K, although the pseudo-second-order model also showed an adequate fit, particularly at 293 K. This indicates that, while the pseudo-first-order model is generally more suitable under these conditions, the pseudo-second-order model may also apply under certain circumstances. The results of the batch experiments demonstrate that iron oxide-coated ignimbrite is a promising adsorbent for effectively reducing high concentrations of As(V) in contaminated water. [ABSTRACT FROM AUTHOR]

To constrain the age and duration of large-scale caldera-forming eruptions, we measured paleomagnetic directions of pyroclastic deposits from the 30 ka Aira caldera eruption sequence, and the 60–45 ka Iwato pyroclastic flow deposits around Aira caldera in southern Kyushu, Japan. The 30 ka Aira caldera eruption sequence consists of Osumi pumice fall (OS), Tarumizu pyroclastic flow deposit (TM), Ito ignimbrite (IT) and co-ignimbrite ash (AT), in ascending order. Oriented samples were collected by drilling for OS, TM and welded ignimbrites, and by cubing for non-welded (unconsolidated) pyroclastic flow deposit. We systematically sampled Ito ignimbrite with the degree of welding as: non-welded (IT1), moderately welded (IT2), and strongly welded (IT3) facies that is limitedly distributed in north of Aira caldera. Mean paleomagnetic directions of OS, TM, IT1 and IT2 are consistent with those previously reported for AT and welded facies of IT. Although OS samples were collected from multiple pumice clasts at proximal locations, we obtained well-defined mean paleomagnetic directions corresponding to those of co-eruptive pyroclastic flow (TM). This suggests that even clast-supported and non-welded pumice fall can retain thermoremanent magnetization at the time of deposition. Significance tests for our mean paleomagnetic directions showed that of all sequential units of the Aira caldera-forming eruption deposits, only IT3 has a different paleomagnetic direction. Based on reported paleosecular variation changing rates in Japan, and on the angular difference associated with error of the two paleosecular directions, we estimate the time gap between IT3 and IT2, to be 24.3 ± 16.3 years. A conductive cooling model explains this time difference as due to differences in cooling time between quickly, and slowly cooled parts of a thick single ignimbrite unit. Although the possibility that multiple flow units occurred within tens of years of each other cannot be excluded, there are no observations of clear flow unit boundaries in the Ito ignimbrite to support the suggestion that the Aira caldera-forming eruption sequence was deposited within a shorter time than years. In addition, the age of Iwato pyroclastic flow deposit, which has been situated between 60 and 45 ka, was estimated by calculating the angular distance between the mean paleomagnetic direction and the modeled secular variation curve from the GGF100 ka. As the result, we determine the most probable age to be around 56 ka. [ABSTRACT FROM AUTHOR]

Highlights The possibility of rotomolding polypropylene (PP) composites with high loadings of a silica‐based dust of ignimbrite, a byproduct of volcanic stone extraction is demonstrated. This study aims to establish the properties of composites with various ratios of mineral dust as a filler in PP matrices at loadings from 5 to 30 wt%, ultimately transforming mining residues into a valuable resource for composite production and creating a value chain around the traditional mining industry. Once the composites were obtained, they were subjected to several characterization techniques to comprehensively assess their mechanical and thermal properties. In general, a high percentage of ignimbrite powder has resulted in a reduction in the mechanical properties of neat PP, although no significant changes were observed for composites at lower loadings. Furthermore, the incorporation of this mineral material modified the thermal properties of the PP, enhancing its thermal stability. The blending of the matrix and filler resulted in a reduction in both the melting crystallization temperatures for highly‐filled composites. Rotomolded items with good aesthetics, with stone‐like appearance, were obtained without any modification on the mineral dust or even without any melt compounding, therefore not increasing the energy consumption during the composites production. Composites production is a suitable strategy for valorization of mineral residues. Welded ignimbrite residual dust has been used for the first time in composites. Mineral dust has been successfully used in composites obtained by rotomolding. Polypropylene with up to 30% of the stone dust can be processed. Good aesthetics and mechanical features can be obtained with mineral wastes. [ABSTRACT FROM AUTHOR]

Groundwater resource in the "Larena Plain" at the western margins of the Southern Main Ethiopian Rift (SMER) was investigated using integrated geophysical techniques—electrical resistivity and magnetic methods. The objective was to assess aquifer depth, extent, and geological controls in the study area. Vertical electrical sounding (VES) was employed to examine and map aquifer depth and lateral extension, while geological structures and lithological contacts influencing groundwater flow and accumulation were identified using magnetic surveys. Two‐stage aquifers were identified: a deeper fractured ignimbrite and a volcanoclastic sediment aquifer covered by shallow weathered ignimbrite. The depths and distributions of these aquifers were mapped, with geological structures generally aligned in the NNE–SSW orientation. Understanding these geological structures and aquifer systems is crucial for effective groundwater management in the "Larena Plain," providing valuable insights for regional hydrogeological studies. [ABSTRACT FROM AUTHOR]

Introduction: This work employs a coupled evaluation model that integrates deterministic coefficients with the Analytic Hierarchy Process to conduct a comprehensive assessment of geological disaster susceptibility in Shenzhen Town, Ninghai County. Methods: Cascading geological disasters induced by typhoons and rainfall in the southeast coastal area of China are a major concern and cause huge losses of life and property every year. To effectively prevent and mitigate such disasters, it is necessary to evaluate the susceptibility of geological disasters. Taking geological disasters in Shenzhen Town, Ninghai County as the research object, eight influencing factors in terms of topographic and geomorphological conditions, engineering geological conditions, and human activities were selected based on the geographic information platform (GIS) in this work. The coupling model of the certainty factor model and analytic hierarchy process method was used to evaluate the susceptibility of geological hazards in the study area. Results: The evaluation results illustrate that the coupling model can accurately and objectively assess the susceptibility of geological hazards in this region, with a high evaluation accuracy of 80.8%. The susceptibility is greatly affected by slope, stratigraphic lithology, and human activities. The areas with extraordinarily high and high susceptibility were identified in the northwestern part of the study, where the ignimbrite is exposed in the steep topography. Discussion: The research method provides a reference for evaluating the susceptibility of geological hazards in the southeastern coastal region of China, and the evaluation results can provide recommendations for decision-making on disaster prevention and mitigation in this region. [ABSTRACT FROM AUTHOR]

The seismic-stratigraphic analysis of single-channel seismic profiles does not provide reliable information on the nature of the materials identified in the absence of direct investigations; therefore, it is often affected by interpretative subjectivity. In this work, we use the 2D Fast Fourier Transform, applied to samples extracted from areas of interest, as a method to obtain a database of signatures (characterisation indices) for post-processing identification of geological units. This method is applied to discriminate Holocene marine units from volcanoclastic units present in the geological records of the Gulf of Naples. The results show how the signatures of these units are specific and, consequently, can be well distinguished using the proposed method. The method is corroborated by the statistical analysis carried out on single shots extracted from the seismic lines. Although the proposed method may lead to misinterpretations in some specific cases, as discussed in the paper, it offers geologists important help in rapidly and effectively classifying seismic units. [ABSTRACT FROM AUTHOR]

Sela Dingay kaolin deposit is a primary deposit formed mainly through the weathering of rhyolitic ignimbrite. Integrated analyses of geological, mineralogical, geochemical and physical properties were conducted to characterise the industrial applications of Sela Dingay kaolin. X-ray diffraction (XRD) and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) were used to characterise the raw kaolin samples. The results show that Sela Dingay kaolin is mainly composed of kaolinite (66–93%) and quartz (9–34%). The higher chemical index of alteration (CIA = 94.2%) and chemical index of weathering (CIW = 96.8%) values suggest that Sela Dingay kaolin was formed by intense chemical weathering under oxidising conditions. Sela Dingay kaolinite deposit consists of high percentage of clay/silt-sized particles, a low shrinkage value (1.1–3.4%), medium-high plastic limit (25–35%), with specific gravity and pH values ranging between 2.47 and 2.56 g/cm3 and 6.3 and 7.2, respectively. The overall results show that Sela Dingay kaolin is medium to high grade and it can be used for various industrial applications with appropriate beneficiation processes to remove higher amounts of Fe2O3 and quartz. Therefore, the newly discovered kaolin deposit (estimated at 5,136,166 tonnes) in the Sela Dingay area is a potential target for future kaolin exploitation. [ABSTRACT FROM AUTHOR]

Physical wear during bedload transport influences downstream changes in the size distributions and shapes of riverbed sediment, which in turn affect myriad fluvial processes ranging from incision into bedrock to provision of aquatic habitat. Here we use laboratory tumbling experiments to address several remaining knowledge gaps, including the roles of lithologic susceptibility to fragmentation, particle size distributions and particle angularity in controlling wear rates and the size distribution of wear products. To focus on the dynamics of particle wear in headwater channels, we used initially angular sediment and ran the experiments until 10% of the initial bedload particle mass had been lost to fine‐grained wear products. We measured individual particle mass and diameter by hand and used photo analysis to quantify particle shape and angularity. We find strikingly different wear patterns between limestone and welded tuff. Although wear rates in the tuff were an order of magnitude slower than the limestone, tuff wear was primarily by fragmentation while limestone wear was dominantly by attrition. Fragmentation of the tuff resulted in a widening of the bedload size distribution, a lack of consistent particle rounding and a fine‐wear product dominated by sand. In contrast, limestone particles rounded substantially and produced silt‐sized wear products. Differences in wear product size and susceptibility to fragmentation may reflect contrasts in the size distribution of mineral crystals in each lithology. Wear rates in both rock types declined substantially with increasing cumulative mass loss, due to rounding in the limestone and reduced fragmentation in the tuff. These results suggest that applications of the conventional exponential model to predict mass loss with travel distance need to account for lithologic influence on susceptibility to fragmentation and the influence of rounding on particle wear rates. [ABSTRACT FROM AUTHOR]

Processes of transport and deposition of large-scale pyroclastic density currents, which transport 102-103 km3 of material, are still poorly understood. The volcanic explosivity index (VEI) 7 Campanian Ignimbrite pyroclastic density current is one such poorly understood case that is subject to lively scientific debates about its origin and processes. The Campanian Ignimbrite is related to the 39.8 ka eruption that formed the partly submarine and active Campi Flegrei caldera in Italy. The related pyroclastic density current extended over an area of more than 6000 km2 on land around the caldera, with a final runout of ~75 km, and surmounted mountain ridges higher than 1000 m above sea level, even at distal reaches. We used physical characteristics of the ignimbrite to understand the transport and emplacement dynamics of the Campanian Ignimbrite pyroclastic density current. Thickness, mass, and clast-size distributions across paleotopography were used to infer that the main transport system was a dilute, density-stratified pyroclastic density current, which was at least 1.5 km thick, which was short-lived (possibly as short as ~20 min), and which had a mass flow rate of ~1011 kg/s. At its base, high-concentration undercurrents formed and interacted with the rough paleotopography, laying down a low-aspect-ratio ignimbrite sheet when on flat plains, but generating back-flows from ridges and channeling in paleovalleys. The deposit is predominantly a massive valley-pond ignimbrite facies, even across rough mountain terrains. The absence of veneer facies on steep slopes reflects the near-Newtonian rheology of the undercurrents, interpreted as fluidized dense granular flows. This work advances the interpretations of pyroclastic density current deposits, which do not necessarily directly reflect conditions in the transport system. [ABSTRACT FROM AUTHOR]

Caldera-forming eruptions represent extremely hazardous events. The Loch Bà Caldera on the Isle of Mull, NW Scotland, preserves an ~120 m thick sequence of Palaeogene silicic pyroclastic rocks and collapse breccias. Here we present the first detailed account of the lithostratigraphy and architecture of the caldera-fill. A silicic explosive eruption generated pyroclastic density currents that deposited a range of rhyolitic ignimbrite lithofacies as the caldera collapsed. Abrupt changes in ignimbrite lithofacies and lateral thickness changes are attributed to volcano-tectonic faults and incremental collapse of the caldera. Five eruption phases have been recognised that record rapid switching between sustained high-fountaining and low-fountaining “boil-over” eruptions. The ignimbrites are unconformably overlain by mesobreccias and inward rotated megablocks of basalt lava country rock, which record catastrophic inward collapse of the caldera walls and margins. Our results provide new insights into caldera collapse and intra-caldera-fill that can be applied to other volcanoes worldwide.

Absract: Rawa Danau Volcanic Complex (RDVC) in the western part of Banten—Western part of Java Island, Indonesia, holds records and histories of past violent volcanic eruption. These past volcanic activities manifested as huge Rawa Danau caldera and massive Banten Tuff pyroclastic deposits that are distributed for more than ten kilometres away from the source and have played an important role in shaping the morphology of Banten. Previous studies suggest that Banten Tuff is composed of various pumiceous pyroclastic deposits presumably formed in Early Pleistocene. The deposits cover vast area of Banten, and their thickness exceeds 200 m. Despite their significance, there are no detailed studies that discuss the stratigraphic and eruption dynamics of the deposits. This paper provides new insight on the eruption dynamics based on fieldwork observation, volcanic stratigraphy, and petrologic interpretation. The study focuses on the eastern flank of RDVC, where the well-preserved stratified outcrops are located. Aligned with previous studies, the deposit can be divided into two major eruption sequences: 1) Lower Banten Tuff (LBT) and 2) Upper Banten Tuff (UBT). LBT is interpreted as lithic-bearing ignimbrite with accompanying surge deposit and considered as a single-phase eruption. Lithic-rich characteristics in this unit suggest that LBT might be related to the caldera-forming mechanism. On the other hand, UBT shows a more dynamic sequence. It is composed of two fallout units followed by an ignimbrite formed by the eruption column collapse. The appearance of banded pumice in UBT with contrasting andesitic and rhyolitic compositions suggests a mafic injection as the eruption trigger. Pumice and ash compositions are mostly in dacitic to rhyolitic range, with several samples in andesitic range. Componentry analysis suggests that all eruptions were magmatic in origin. [ABSTRACT FROM AUTHOR]

The main goal of active fault investigation is obtaining evidence of the Quaternary fault activity through trenching. To accomplish this, electrical resistivity surveys are widely utilized to accurately detect faults buried beneath alluvium. In this study, 2D and 3D electrical resistivity surveys were conducted at the Miho site of the southern Yangsan Fault, the Quaternary active fault area already well-studied via trench investigations. The efficacy of electrical resistivity surveys for fault detection was examined by comparing the resistivity distributions against data in the trench logs. At the Miho site, three lines were installed for the 2D electrical resistivity survey and 22 lines were set within a 27 × 27 m square area for the 3D electrical resistivity survey. The length of each survey line was 27 m with an electrode spacing of 1 m. A dipole-dipole array was used to measure the potential difference between each measurement electrode using the same transmitted current and voltage. To derive the 2D and 3D resistivity distributions from the data acquired in the field, the inversion programs DC_2DPRO and DC_3DPRO were employed. Comparison of the 2D resistivity distribution with trench log data shows that the zone of dacitic welded tuff west of the Quaternary fault plane has relatively high resistivity, while the zone of foliate gouge and breccia derived from sedimentary rocks east of the Quaternary fault plane has a low resistivity of less than 40 Ω·m. From these results, it is evident that the method is effective, particularly when different rock types are distributed on either side of the fault boundary or when highly conductive materials, such as clay-rich fault gouges, are present within the fault zone. The resistivity distribution in the 3D survey area can be depicted using both block diagrams and depth-specific slices, facilitating a spatial understanding of the continuity of fault (or fracture) zones. Consequently, this study demonstrates that 3D surveys offer numerous advantages over 2D surveys by accurately capturing planar structures and enabling spatial interpretation based on 3D resistivity distribution. [ABSTRACT FROM AUTHOR]

Ignimbrites have been widely used as building materials in many historical and touristic structures in the Kayseri region of Türkiye. Their diverse colours and textures make them a popular choice for modern construction as well. However, ignimbrites are particularly vulnerable to atmospheric conditions, such as freeze-thaw cycles, due to their high porosity, which is a result of their formation process. When water enters the pores of the ignimbrites, it can freeze during cold weather. As the water freezes and expands, it generates internal stress within the stone, causing micro-cracks to develop. Over time, repeated freeze-thaw (F-T) cycles lead to the growth of these micro-cracks into larger cracks, compromising the structural integrity of the ignimbrites and eventually making them unsuitable for use as building materials. The determination of the long-term F-T performance of ignimbrites can be established after long F-T experimental processes. Determining the long-term F-T performance of ignimbrites typically requires extensive experimental testing over prolonged freeze-thaw cycles. To streamline this process, developing accurate predictive equations becomes crucial. In this study, such equations were formulated using classical regression analyses and artificial neural networks (ANN) based on data obtained from these experiments, allowing for the prediction of the F-T performance of ignimbrites and other similar building stones without the need for lengthy testing. In this study, uniaxial compressive strength, ultrasonic propagation velocity, apparent porosity and mass loss of ignimbrites after long-term F-T were determined. Following the F-T cycles, the disintegration rate was evaluated using decay function approaches, while uniaxial compressive strength (UCS) values were predicted with minimal input parameters through both regression and ANN analyses. The ANN and regression models created for this purpose were first started with a single input value and then developed with two and three combinations. The predictive performance of the models was assessed by comparing them to regression models using the coefficient of determination (R2) as the evaluation criterion. As a result of the study, higher R2 values (0.87) were obtained in models built with artificial neural network. The results of the study indicate that ANN usage can produce results close to experimental outcomes in predicting the long-term F-T performance of ignimbrite samples. [ABSTRACT FROM AUTHOR]

Understanding the origin of Late Jurassic volcanism in southern Patagonia is crucial for unraveling the early Andean orogenic evolution. However, radiometric dating is not connected to stratigraphic analysis along the South Patagonian Andes, which obscures the real duration of the Late Jurassic magmatic activity. In this contribution, we present the results of a volcanic stratigraphy analysis, complemented by structural and petrographic data, on a thick succession of acidic volcanogenic rocks in the Laguna Verde district of southern Chile located along the south shore of General Carrera-Buenos Aires Lake. Through the recognition of igneous stratigraphy, we strategically sampled representative volcanogenic rocks that cover the entire duration of eruptive activity. By doing so, the new U–Pb zircon magmatic ages, combined with a compilation of U–Pb crystallization ages from the South Patagonian Andes, allows us to constrain the volcanic activity in the study area to a period of 8 My (~ 155–146 Ma, V3 stage) and 11 My considering age inherent errors. The field recognition of normal faults and the syn-kinematic emplacement of sub-volcanic bodies, which are inferred to conform to a ring-fault system, along with the presence of a thick succession of ignimbrites, suggest that the syn-extensional volcanic emplacement occurred in a caldera volcanic environment. This setting was responsible for the short-lived, voluminous eruptions. Furthermore, the high Th/U zircon ratios identified for the ~ 155–150 Ma period indicate the climax of extensional tectonics. The integration of these data supports the hypothesis that retreating-mode subduction played a major role in producing ignimbrite flare-ups. [ABSTRACT FROM AUTHOR]

The contribution of sediment transport and accumulation to soil formation was investigated in an area characterized by continental sedimentary activity since the Late Pleistocene. The area was the north-eastern portion of the large Quaternary graben represented by the Campania Plain, which is rimmed to the north–east–south by the Mesozoic carbonate Apennine nappes. The plain was filled mainly by products generated by eruptions from the Phlegrean Fields, which were also distributed on the slopes bordering the plain and remobilized toward the adjacent surfaces. Five sites were selected in the area in question. They were studied using morphological features and pertinent characteristics of the mineral soil fraction >2.0 mm, such as their volume and lithological description. Soils were compared to selected lithostratigraphic sequences characterizing the studied area, which were collected from literature and reinterpreted in pedological keys. The results showed that soils derived from the emplacement of Phlegrean primary volcanic materials, such as Campania Ignimbrite (~39–40 ky B.P.) and Neapolitan Yellow Tuff (~15 ky B.P.), with the related weathering products, and from volcanic materials reworked and transported by alluvial/colluvial episodes. The latter formed contrasting soil horizons which, differing in both rock fragment content and lithological composition, testified to the presence of lithological discontinuities. The formation of the horizons in question interrupted the genetic sequence derived from the in situ alteration of the volcanic substrata, suggesting that processes of transport and redistribution of sediments from the adjacent mountain slopes contributed to soil formation. The comparison of the pedostratigraphies with the lithostratigraphic sequences indicated a strong relation between geomorphic and pedogenetic events. [ABSTRACT FROM AUTHOR]

In this study, we explored the impacts of radiation damage and chemical composition on the etching time of fission tracks in monazite. Despite the potential of monazite fission-track (MFT) dating as an ultralow-temperature thermochronology, the comprehensive effects of radiation damage and non-formula elements, especially on the etching rate of MFTs, remain unexplored, and established analytical procedures are lacking. We quantified the degree of radiation damage (ΔFHWM) in Cretaceous to Quaternary monazites distributed in the Japan arc through Raman spectroscopy and chemical composition analyses. Subsequently, MFT etching was performed to examine the correlation between these parameters and the etching time. Estimation of the degree of radiation damage showed an increase in radiation damage corresponding to the cooling age of each geological unit. For example, the Toya ignimbrite (ca. 0.1 Ma) and the Kurobegawa granodiorite (< 0.8 Ma), both of which are types of monazite from Quaternary geological units, have ΔFHWM values of 0.27 and 0.55 cm -1 , respectively. In contrast, the Muro ignimbrite (ca. 15 Ma) has a ΔFHWM value of 4.01 cm -1 , while the Kibe granite and the Sagawa granite, both of which are Cretaceous granitoids, yielded 7.35 and 6.31 cm -1 , respectively. MFT etching of these samples according to the existing recipe (6 M HCl at 90 °C for 60–90 min) was completed at 1200, 860, 210, 120, and 90 min for the Toya ignimbrite, Kurobegawa granodiorite, Muro ignimbrite, Sagawa granite, and Kibe granite, respectively. These outcomes highlight an inverse relationship between MFT etching time and the degree of radiation damage in monazite, while the correlation between MFT etching time and chemical composition was unclear. The results affirm earlier considerations that the etching rate of MFTs is strongly influenced by radiation damage. Conversely, young samples with lower levels of radiation damage exhibit higher chemical resistance, suggesting that existing etching recipes may not adequately etch MFTs. [ABSTRACT FROM AUTHOR]

Pyroclastic density currents are complex mixtures of rock, ash and gas and represent significant hazards at many active volcanoes worldwide. Ignimbrites are the deposits of pyroclastic density currents and can be used to record the eruption dynamics and the interaction of the current with the landscape over time and space. The Sròn Mhòr Member in Ardnamurchan, NW Scotland, is a newly documented sequence of silicic Paleocene ignimbrites. Five phases of eruption are recorded by the ignimbrites, which range from non-welded to welded to lava-like. Between each eruption phase, a period of non-deposition occurred, during which rapid erosion and incision took place. The ignimbrites record how pyroclastic density currents of different temperature, grain size, rheology, and composition interacted with the landscape, filling ancient valleys and lakes, before switching to or re-establishing new drainage pathways. Our results provide further insight into ignimbrite deposition that can be applied to volcanoes worldwide.

Hydration fronts penetrate 50-135 µm into glassy rhyolite embayments hosted in quartz crystals from the Mesa Falls Tuff in the Yellowstone Plateau volcanic field. The hydration fronts occur as steep enrichments that reach 2.4 ± 0.6 wt% H2O at the embayment opening, representing much higher values than interior concentrations of 0.9 ± 0.2 wt% H2O. Molecular water accounts for most of the water enrichment. Water speciation indicates the hydration fronts comprise absorbed meteoric water that modified the original magmatic composition of the rhyolitic glass. We used finite difference diffusion models to demonstrate that glass rehydration was likely produced over a few decades as the ignimbrite cooled. Such temperatures and time scales are consistent with rare firsthand observations of decadal hydrothermal systems associated with cooling ignimbrites at Mount Pinatubo (Philippines) and the Valley of Ten Thousand Smokes (Alaska). [ABSTRACT FROM AUTHOR]

The Aurignacian is the first European technocomplex assigned to Homo sapiens recognized across a wide geographic extent. Although archaeologists have identified marked chrono-cultural shifts within the Aurignacian mostly by examining the techno-typological variations of stone and osseous tools, unraveling the underlying processes driving these changes remains a significant scientific challenge. Scholars have, for instance, hypothesized that the Campanian Ignimbrite (CI) super-eruption and the climatic deterioration associated with the onset of Heinrich Event 4 had a substantial impact on European foraging groups. The technological shift from the Protoaurignacian to the Early Aurignacian is regarded as an archaeological manifestation of adaptation to changing environments. However, some of the most crucial regions and stratigraphic sequences for testing these scenarios have been overlooked. In this study, we delve into the high-resolution stratigraphic sequence of Grotta di Castelcivita in southern Italy. Here, the Uluzzian is followed by three Aurignacian layers, sealed by the eruptive units of the CI. Employing a comprehensive range of quantitative methods—encompassing attribute analysis, 3D model analysis, and geometric morphometrics—we demonstrate that the key technological feature commonly associated with the Early Aurignacian developed well before the deposition of the CI tephra. Our study provides thus the first direct evidence that the volcanic super-eruption played no role in this cultural process. Furthermore, we show that local paleo-environmental proxies do not correlate with the identified patterns of cultural continuity and discontinuity. Consequently, we propose alternative research paths to explore the role of demography and regional trajectories in the development of the Upper Paleolithic. [ABSTRACT FROM AUTHOR]

Welded tuffs have a wide range of welding degrees and show significant variability in mechanical behavior. However, the detailed influence of welding degree on the meso-mechanical behavior of welded tuffs remains unclear. Based on petrographic and pore-structure analysis, we conducted a series of meso-mechanical experiments on weakly to strongly welded tuffs by utilizing a mesoscale real-time loading-observation-acquisition system. The results indicated that the strongly and weakly welded tuffs showed a small range in mineralogical composition and porosity, while the meso-mechanical behavior exhibited significant variability. Strongly welded tuffs showed lower uniaxial compression strength, weaker mechanical anisotropy, and smaller fracture surface roughness. In contrast, weakly welded tuffs exhibited higher uniaxial compression strength, stronger mechanical anisotropy, and rougher fracture surface roughness. Welded tuffs with strong packing and welding of glass shards tended to have fractures propagating along the maximum principal direction, while those with weak packing and welding of glass shards may have had failure along the alignment of glass shards. The influence of welding degree on the meso-mechanical behavior of welded tuffs probably originates from their diagenesis environments, mainly depending on the combined effect of the pyroclastic properties and pseudo-rhyolitic structure. The findings reveal the meso-mechanical differences of welded tuffs and shed light on improving tuffs for stable and durable construction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four rhyolitic explosive eruption events were distinguished from 13.1 Ma to 11.6 Ma. • Silicic volcanism occurred at termination of subduction in a thinning lithosphere. • Rhyolites show extreme magma differentiation and reduced-dry character. • Zircon trace element and Hf isotope fingerprint is an effective correlation tool. The Tokaj Mts. volcanism occurred in a thinning continental lithosphere regime at the final stage of the subduction process. Using high-precision zircon U-Pb dating, four major explosive eruption events were distinguished. Among them the 13.1 Ma Sátoraljaújhely and the 12.0 Ma Szerencs eruptions could have yielded large amount of volcanic material (possibly > 100 km3) and they were associated with caldera collapse as shown by the several hundred-metre-thick pyroclastic deposits and the long (>100 km) runout pyroclastic flow in case of the 13.1 Ma eruption. The 12.3 Ma Hegyköz and the 11.6 Ma Vizsoly eruptions were relatively smaller. The volcanic products can be readily distinguished by zircon and glass trace elements and trace element ratios, which can be used for fingerprinting and to correlate with distal deposits. The Rb, Ba, Sr content and strong negative Eu-anomaly of the glasses reflect extreme crystal fractionation, particularly for the Szerencs rhyolitic magma. The silicic volcanic products of the Tokaj Mts. show compositional similarities with the so-called 'dry–reduced–hot' rhyolite type consistent with an origin in an extensional environment, where the primary magmas were formed by near-adiabatic decompression melting in the mantle with subordinate fluid flux. In contrast, some of the older Bükkalja rhyolitic magmas evolved via more hydrous evolutionary paths, where amphibole played a role in the control of the trace element budget. The significant increase of zircon ε Hf values from −8.8 to + 0.2 in the rhyolitic pyroclastic rocks of Tokaj Mts. with time implies that mantle-derived magmas became more dominant. This can be explained by the specific tectonic setting, i.e. the final stage of subduction when the descending subducted slab became almost vertical, which exerted a pull in the upper lithosphere leading to thinning and accelerated subsidence as well as asthenospheric mantle flow just before the slab detachment. [ABSTRACT FROM AUTHOR]

We analyzed mineralogical characteristics, and major as well as rare earth element concentrations, from a cryptotephra layer in sediments of the infilled maar of Auel (Eifel, Germany). The results of detailed geochemical analyses of clinopyroxenes and their glassy rims from the Auel cryptotephra layer showed that they are similar to those from the thick Campanian Ignimbrite tephra occurrence in a loess section at Urluia (Romania). Both tephras show idiomorphic green clinopyroxenes and formation of distorted grains up to millimeter scale. The cryptotephra in the Auel core has a modelled age of around 39,940 yr b2k in the ELSA-20 chronology, almost identical to the latest 40Ar/39Ar dates for the Campanian Ignimbrite/Y-5 (CI/Y-5) eruption. These observations suggest that parts of the CI/Y-5 ash cloud were transported also northwestward into Central Europe, whereas the main branch of the CI/Y-5 ash plume was transported from southern Italy towards the NE, E, and SE. Based on pollen analyses, we conclude there was no direct effect on vegetation from the CI/Y-5 fallout in the Eifel area. Trees, shrubs, and grasses remained at pre-tephra-airfall levels for roughly 240 years, but changed around 39,700 yr b2k when thermophilic woody plants (e.g., Alnus and Carpinus) disappeared and Artemisia spread. This change in vegetation was well after the Laschamp geomagnetic excursion and also after the GI9 interstadial and quite probably represents the onset of the Heinrich Event 4 (H4) cold spell, when climatic conditions over the North Atlantic, and apparently also in Central Europe, deteriorated sharply. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the present work, a TiO2/zeolite photocatalyst was synthesized by dispersing TiO2 nanoparticles obtained through the sol-gel method onto the surface of natural zeolite derived from ignimbrite residue. The zeolite was obtained from an ignimbrite rubble treatment collected from a quarry in Arequipa City, Peru. The research focused on the effect of zeolite on the TiO2 nanoparticles. The synthesized photocatalysts were characterized using various techniques, including field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDS), X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and Brunauer–Emmett–Teller surface area analysis (BET). The results revealed that the TiO2/zeolite samples displayed high crystallinity, with TiO2 being present in three phases and zeolite being present in the analcime phase. Furthermore, these samples exhibited a band gap of 3.14 eV and a high surface area compared to that of bare TiO2. Finally, the photocatalytic activity of the TiO2/zeolite composite obtained was evaluated toward the decomposition of 10 ppm and 20 ppm of methyl orange (MO) dye. The TiO2/zeolite samples demonstrated improved photocatalytic activity compared to that of pristine TiO2 under the same experimental conditions. This enhancement is primarily attributed to the increased specific surface area of the TiO2/zeolite samples, making them promising materials for future efficient and sustainable photocatalytic applications. [ABSTRACT FROM AUTHOR]

The Ora Ignimbrite (~275 Ma) is a crystal-rich (~40%), heterogeneous, supereruption-sized (~1300 km3) rhyolite in northern Italy and the final eruptive product of the Athesian Volcanic Group (289–274 Ma), the largest Permian volcanic district in Europe. Two key outcrops, an intracaldera vitrophyre and an outflow vitrophyre, contain well-preserved, glass-bearing juvenile material. We investigate at what scale heterogeneities existed in the Ora magmatic system by studying the geochemical and petrological characteristics of crystal-rich (20–50%) and crystal-poor (<20%) fiamme from the Ora vitrophyres, allowing us to reconstruct critical aspects of Ora's magmatic architecture and pre-eruptive history and granting us further insight into the storage and dynamic processes that occur in large, crystal-rich, silicic systems. Textural analysis of fiamme reveals four types: the intracaldera vitrophyre has very coarse-grained crystal-rich (VCCR) and fine-grained crystal-poor (I-FCP) fiamme, while the outflow vitrophyre has coarse-grained crystal-rich (CCR) and fine-grained crystal-poor (O-FCP) fiamme. The diversity of crystal-poor (I-FCP & O-FCP) fiamme glass trace-element compositions suggests that multiple small crystal-poor magma bodies were dispersed throughout the Ora magmatic system. Compositionally and texturally distinct glass types in single O-FCP fiamme preserve evidence of variable degrees of magma mixing and record different mingling to eruption timescales, revealing that the Ora magmatic system experienced multiple silicic recharge events. In the crystal-rich (VCCR & CCR) fiamme, high crystal contents (VCCR: 40–50%; CCR: 20–40%), large crystals (max grain size: VCCR: 4–10 mm; CCR: 3–4 mm), and interlocking growth textures suggest that these fiamme contain parcels of disaggregated magma mush. High-silica rhyolite glass compositions (77.2–78.3 wt.% SiO2) and extremely depleted Sr (VCCR: <20; CCR: <5 ppm) and Ba (VCCR: <70; CCR: <20 ppm) glass trace-element concentrations indicate that the crystal-rich fiamme glasses represent highly fractionated melts. Crystal-rich fiamme glass trace-element compositions also form discrete, tightly clustered populations, suggesting that multiple crystal-rich, melt-dominated magma bodies existed prior to eruption. We propose that the coexistence of large-scale heterogeneity (e.g. deposit-scale and outcrop-scale) with small-scale homogeneity observed in crystal-rich fiamme is resolved by a model in which at least two separate magma reservoirs, each containing multiple melt-dominant magma bodies, erupted to form the Ora Ignimbrite. [ABSTRACT FROM AUTHOR]

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The Eastern Caucasus Mountains in Georgia include products from extensive Miocene volcanic activity that are being unraveled by geological mapping supported by geochronology and geochemistry. This article presents new zircon U–Pb geochronology and whole rock geochemistry of the volcanic ash layers of the intermountain Neogene basin of the Eastern Caucasus. Our investigation in the region demonstrates that these ash layers, whose eruption center(s) have not been identified yet, has age and geochemical characteristics of the Mtkvari (Kura) ignimbrite of the Samtskhe-Javakheti volcanic highland. This study shows that zircons from both formations crystallized at the same time ~ 7.50 Ma ago and have geochemical and morphological similarity. Taken together with the geography of the region (200–300 km from the volcanic source to the sedimentary basins), it is likely that the source of the ash layers was the Upper Miocene volcanic eruptions on the Samtskhe-Javakheti volcanic highlands. Based on the distribution, thickness, and age of the volcanic ash layers and the analysis of the structure and scale of the Mtkvari ignimbrite, the widely distributed ash likely resulted from a Plinian-type eruption in the Samtskhe-Javakheti volcanic highland. These eruptions led to the formation of the large-scale caldera structure (Niala caldera) and the Mtkvari ignimbrite. The inferred caldera extends to the northeastern territory of Türkiye (Turkey), i.e., NE of the Kars Plateau. Ideally, this western portion of the caldera and volcanic highlands can be characterized in the future, and a unified structure model of this volcanic center can be established. [ABSTRACT FROM AUTHOR]

Ignimbrite rock is a volcanic material located in the Arequipa region (Peru), and for centuries, it has been used as a construction material, giving a characteristic light pastel, white to pink color to the city of Arequipa, with white being the most common. In the present study, the potential use of three types of Arequipa raw materials (ignimbrite rock powder, calcined clay powder, and demolition mortar powder) as the main source of new binders or the manufacture of environmentally friendly mortars, without the addition of ordinary Portland cement (OPC) is discussed. In this work, an in-depth characterization of the materials used was carried out. The proposed fabrication route for geopolymeric materials was considered for the manufacture of binders and mortars using an alkaline solution of NaOH with values between 12 and 18 molar, as a trigger for the geopolymerization process. Geopolymeric mortars were obtained by adding a controlled amount of fine sand to the previously prepared mixture of binder raw material and an alkaline solution. Conventional OPC and geopolymeric mortars manufactured under the same conditions were mechanically evaluated by uniaxial compression tests at a constant compression rate of 0.05 mm/min and under normal conditions of temperature and atmosphere, where the most optimal values were obtained for 15 molar alkaline solutions of ignimbrite without the addition of aggregates, with values of compressive strength of 42 MPa and a modulus elastic of 30 GPa. The results revealed a significant increase in the maximum strength and modulus of elasticity values when the volumetric fractions of OPC are completely replaced with geopolymeric binders in the study conditions of this work, demonstrating the enormous potential of the ignimbrite rock and construction waste studied, as raw material of alternative mortar binders without the addition of OPC. With this work, the ignimbrite rock, of great value in the region and also found in other areas of the Earth's geography, was characterized and valued, in addition to the calcined clay and demolition mortar of the region. [ABSTRACT FROM AUTHOR]

Atera Fault clay gouges were collected for age dating near Kawaue, Nakatsugawa City, Central Japan, and the results integrated within its complex geological history. The results form an internally consistent data set constrained by extensive geochronological data (AFTA, ZFTA, CHIME) and support the application of gouge dating in constraining timing of brittle deformation in Central Japan. The Atera illite age data complete recently obtained limited illite fault gouge age data from underground exposure in the Toki Granite; the new illite age data are identical within error. The age of the heterogenous welded tuff breccia zone (Atera 1) ranges from 40.6 ± 1.0 Ma to 60.0 ± 1.4 Ma, whereas ages of the fault core gouge sample (Atera 2) range from 41.8 ± 1.0 Ma to 52.7 ± 1.2 Ma. The finest < 0.1 µm fraction of the fault breccia and fault core gouge yield ages around 41 Ma, identical within error. The new illite age data indicate brittle faulting and a following geothermal event occurring in the Paleogene–Eocene, similar to the nearby Toki Granite area and confirm they were both synchronous with a post-intrusive pluton exhumation. The Atera Fault illite age data provide additional insights into an integrated, regional-scale record of the tectonic displacement of Central Japan and might be influenced by large-scale tectonic processes such as the Emperor sea mount kink around 55 to 46 Ma with fault initiation around 50 Ma and brittle fault cessation or reactivation around 40 Ma in the Eocene. [ABSTRACT FROM AUTHOR]

Our newly acquired and recently published map, geochronologic, and compositional data for early intermediate-composition central volcanoes in the northeastern San Juan Mountains provide insights about the broad magmatic precursors to the large continental-arc ignimbrite flare-up in the mid-Cenozoic Southern Rocky Mountain volcanic field (SRMVF). Initial volcanism migrated from central Colorado to northern New Mexico ca. 40-29 Ma, as part of a more regional trend of southward-progressing mid-Cenozoic magmatism in the U.S. segment of the North American Cordillera. Within the San Juan locus, which represents the largest preserved erosional remnant of the SRMVF and site of most intense eruptive activity, new 40Ar/39Ar and U-Pb zircon ages show that eruptions at many individual edifices began nearly concurrently, at ca. 35 Ma, with peak activity at 34-32 Ma. Broadly similar precursor effusive volcanism characterizes other major loci of continental-arc ignimbrite magmatism along the western American cordilleras, but none of these sites records early volcanism as voluminous, spatially widespread, well exposed, or compositionally diverse as the San Juan locus in Colorado. Early San Juan volcanism was larger in volume than the later ignimbrites, constituting about two thirds the total erupted. Early lava and breccias are as much as 700-900 m thick where exposed along eroded flanks of the San Juan Mountains; drill holes have penetrated sections as thick as 2600 m. The early volcanoes were dominantly andesitic, with lesser dacite and minor rhyolite. Such volcanism is widely interpreted as initiated by basaltic magma from the mantle, but mid-Cenozoic basalt is almost nonexistent at the San Juan locus--an absence inferred to be due to extensive lower-crustal assimilation and fractionation. The early volcanic rocks are calc-alkaline and typical of high-K continental-arc volcanism; they become modestly more alkalic and enriched in trace elements such as light rare earth elements, Zr, Nb, and Th from the San Juan locus northeastward into central Colorado. Such variations may reflect synmagmatic crustal thickening and deeper levels of primary magma generation concurrent with assembly of upper-crustal magma bodies that could support large ignimbrite eruptions. Substantial uncertainties remain for growth histories of the early volcanoes, however, because of unexposed lower parts of edifices, eroded upper parts, and limited availability of mineral phases that could be dated reliably. Although the early volcanoes are widely distributed within the SRMVF, many are clustered at sites of subsequent ignimbrite calderas. The precursor edifices are inferred to record incubation stages in construction of overall translithospheric batholithic-scale magmatic systems. Prolonged processes of incremental magma generation, accumulation, fractionation, and solidification intermittently generated sufficient liquid to erupt large ignimbrites. Maturation of focused eruptions and intrusions was prolonged, 5 m.y. or more, prior to the culminating ignimbrite at some centers in the San Juan Mountains. Some large-volume ignimbrites and related calderas, including the ~5000 km3 Fish Canyon Tuff and associated La Garita caldera, formed as much as several million years later than peak growth of associated precursor volcanoes, recording a sustained interval of diminished eruptive activity as the magma reservoir increased in volume and evolved to more silicic compositions capable of supporting a subsequent large ignimbrite eruption. Dike configurations at early volcanoes that were active nearly concurrently in the SRMVF vary from symmetrically radial to more parallel trends. The contrasting dike geometries are inferred to record possible multiple fluctuations from compressive to weakly extensional regional stress, concurrent with destabilization of the prior flat-slab plate configuration that triggered mid-Cenozoic ignimbrite flare-ups along the Cordilleran margin of the North American plate. These apparent fluctuations in regional stress preceded development of substantial extensional strain in the Southern Rocky Mountain region; outflow ignimbrite sheets of the SRMVF spread across subsequent horst-and-graben structures of the Rio Grande rift without complementary thickness variations. [ABSTRACT FROM AUTHOR]

The 39.8-ka Campanian Ignimbrite was emplaced during a large caldera-forming eruption of Campi Flegrei near Naples, Italy. The ignimbrite is found up to 80 km from the caldera, and co-ignimbrite ash-fall deposits occur 3200 km away. The proximal and distal stratigraphy of the Campanian Ignimbrite has not been definitively correlated due to the dissimilar appearance of the proximal and distal deposits, a lack of medial exposures, and the inconsistency and heterogeneity of the proximal stratigraphy. Here, we document the major-element glass-shard chemistry, matrix componentry, and lithic componentry of the proximal and distal stratigraphic sequences of the ignimbrite to attempt to correlate the units. The results of these disparate observations taken together suggest that the established stratigraphic units cannot be directly and uniquely correlated between the proximal and distal regions and that neither the proximal nor distal stratigraphy provides a record of the entire eruptive sequence. However, the characteristics studied can be used to demarcate eruptive phases that are connected to some of the defined units in the proximal and distal stratigraphy. [ABSTRACT FROM AUTHOR]

The research offers a perspective on the hierarchical facies and the development of an Oligo-Miocene sequence of pyroclastics and lava flows within a continental rift associated with the tectonic activity of the Red Sea. The study deals with genesis, eruption mechanism, magma type, paleo-depositional evolution, and post-depositional history of the studied volcanic rocks overlying the fluviomarine rock sequence of the Jebel Qatrani Formation at Tell El-Zalat, northern Western Desert of Egypt. The study was conducted using an integrated methodology that combines facies analysis and geochemistry. This approach involved field observations, optical polarizing microscopy examination, and the utilization of X-ray fluorescence and energy dispersive X-ray analyses. The present contribution recognizes two facies association represented by lower stratified tuff and upper flood basalt based on their stratigraphic position, lithology, microscopic features, and geochemical attributes. The lower stratified tuff facies is differentiated into three distinct sub-facies that were evolved from calc-alkaline magma and rang in composition from basaltic andesite to rhyolite. Microscopically, the tuff consists of coarse crystal tuff, lithic crystal lapilli tuff, dolomitic coarse crystal tuff, and calcareous-siliceous crystal tuff microfacies. The existence of calcareous body and immiscible calcareous-siliceous zones comprising scattered micro-diamond grains within the lower stratified tuff indicates mantle metasomatism. The upper flood basalt flow was evolved from silica-saturated tholeiitic magma ascent along fissures initiated during Pre-Cambrian and have been reactivated in Oligo-Miocene time. The basalt flow comprises porphyritic olivine basalt and hypocrystalline basalt microfacies types. The alteration in volcanic activity style within Tell El-Zalat area is evident. The shift in the volcanic eruption mechanism is substantiated by the facies hierarchy, with tuffs at the base and basalt lava flow at the summit. The close spatial stratigraphic relationship between the two facies indicates that there were no significant variations in tectonic conditions. [ABSTRACT FROM AUTHOR]

The study area of Rodafnidia on the island of Lesbos (Greece) is considered of archaeological interest, as Paleolithic stone tools have been recovered through excavation and collected from the ground surface in recent years. Geologically, the area is mostly covered by Quaternary post-alpine deposits and volcanic rocks. This paper presents the application of a local geophysical survey to determine the volume of the upper Quaternary deposits in which the Paleolithic artefacts can be found and the identification of their ignimbrite substrates. For this reason, the geoelectrical method was selected as the most appropriate for determining the lithostratigraphic subsurface layers. More specifically, a grid of twenty-one (21) Vertical Electrical Soundings (VES) along with an Electrical Resistivity Tomography (ERT) was carried out. The interpretation of the results of these surveys, in conjunction with the results of older excavation trenches, revealed that the Quaternary deposits have been investigated at depths ranging from 0.5 up to 28.5 meters. Furthermore, the lithological boundary of these post-alpine deposits and their underlying pyroclastic ignimbrite flow (with resistivity 24.0–58.0 Ohm.m) seem to dip to the north. The volume of the Quaternary layer is proposed as the maximum depth for archaeological investigation with high chances to recover more Paleolithic material.

Dome eruptions associated with rhyolitic calderas offer an important insight into how extremely large (> > 10 km3), rhyolitic magma systems are constructed through time. We focus on rhyolitic calderas in the central Taupō Volcanic Zone leading to, during, and immediately following the 350- to 240-ka ignimbrite flare-up. We identified 103 dome eruptions that are dated between ca. 650 and 150 ka and collated 239 literature whole-rock compositions from these domes. For each composition, we modelled the pressure of magma extraction from the magma mush and the mineral assemblage of the mush using the rhyolite-MELTS geobarometer. We calculated extraction temperatures using zircon saturation geothermometry. We show that magmas are extracted from typically quartz-bearing magma mush at a wide range of depths (~50–425 MPa, ~2–16 km) and temperatures (~750°C to ~850°C). Throughout the central TVZ, there are two dominant extraction pressure modes at 1) 150–175 MPa and 2) 250–325 MPa, consistent with 1) the depth of the brittle–ductile transition (~6 km) and just below typical pre-eruptive storage depths of other TVZ magmas (100–150 MPa, ~4–6 km); and 2) partial melt regions imaged below ~8 km by previous geophysical studies. In some regions, there is a clear correlation between crustal structures, the depth of magma extraction, and the composition of the magmas. In the Whakamaru caldera, the domes erupted inside the caldera following caldera collapse are extracted from ~225 to ~350 MPa at ~810°C and have orthopyroxene-bearing compositions dissimilar to the caldera-forming eruption. These domes are aligned along normal faults, suggesting that rifting creates pathways for magma extraction from a deeper mush rejuvenated by recharge. The domes erupted along the structural margins of the Whakamaru caldera have very evolved, hornblende-bearing compositions, similar to the caldera-forming eruption and shallow, colder extraction from ~100 to ~200 MPa at ~770°C, suggesting the mush feeding these domes is a remnant of the older caldera-forming magma system mobilized along the caldera-bounding faults. Two structural levels of magma extraction at ~6 km and 9 to 12 km are persistent throughout the flare-up period and across the central TVZ region, demonstrating the need for further investigation into the factors controlling the depth of mush development. [ABSTRACT FROM AUTHOR]

Hydrothermal eruptions are the most violent and hazardous phenomena within geothermal fields. The largest of these may produce kilometer-sized craters and breccia deposits that are tens of meters thick. The geological and hydrothermal priming that leads to these types of eruptions is poorly understood. To understand large hydrothermal eruptions, we investigated a series of prehistoric events at the Rotokawa geothermal field in New Zealand. By revising the stratigraphy and distribution of hydrothermal breccia deposits and correlating these with componentry, crater morphology, and subsurface geological structure, we estimated the frequency, priming processes, triggers, and dynamics of multiple eruptions. Seventeen large hydrothermal eruptions occurred centuries to millennia apart in the period from ca. 22 cal ka B.P. to ca. 3.4 cal ka B.P. Of six hydrothermal eruptions since ca. 7 ka, four produced oval-shaped craters up to 2 km in diameter, creating a broad, shallow depression within the geothermal field. The two youngest eruptions occurred northeast of earlier eruption centers and have narrower and elongated vents. We infer that in the central depression, newly formed craters rimmed by breccia deposits and high-relief country rock hosted temporary lakes tens of meters deep. Crater-lake breakout(s) and/or seismic events caused sudden pressure reduction above the hydrothermal aquifer, triggering hydrothermal eruptions. Northeast of the basin, hydrothermal alteration produced caprocks above intensively fractured areas. In this case, earthquakes are the most likely trigger for cap-rupture and eruption. All eruptions excavated shallow and large craters mostly within partially altered Oruanui Formation and pre-fragmented breccias. The size and localization of the eruptions was likely due to a combination of (1) availability of undisturbed porous ignimbrite hosting large thermal aquifers, (2) efficient crater excavation within or alongside pre-fragmented breccia, and (3) the location of fracture and fault zones that channeled deep fluid upflow, favoring priming processes. This study highlights how an interplay of tectonic, magmatic, and hydrologic processes is responsible for the timing, dynamics, and ultimate size of hydrothermal eruptions in geothermal fields. Some events may be very large and destructive depending on the right priming and geological conditions. [ABSTRACT FROM AUTHOR]

The paper discusses heritage structures built of welded tuff masonry and timber frames. Such timber-masonry composite structures were built in Japan around the early 20th century. Timber frames are composed of studs and girts. The studs are coupled by penetrating girts via nuki joints. The studs are connected to masonry walls by means of L-shaped wrought iron pegs. In this paper, a warehouse is considered as the case study. Pull-out and shear tests were conducted to examine the performance of joints between a masonry wall and stud. A focus was given to the contribution of iron pegs. A microtremor test was performed on the case study. Based on these experimental activities, seismic analysis was carried out by numerical approach. Attention was paid to the discretisation of joint behaviour between masonry walls and timber studs. The paper introduces structurally a unique heritage building and discusses its seismic behaviour, focusing on joint behaviour derived from iron pegs and nuki joints. Findings are taken advantage of for the seismic analysis of historical composite structures. [ABSTRACT FROM AUTHOR]

There has been considerable dispute over the mode of transport of the Stonehenge bluestones from their multiple sources in West Wales. For a century most archaeologists have accepted that the stones were transported by humans, but a number of earth scientists have taken the view that they were entrained and transported to Salisbury Plain by glacier ice. There is remarkably little evidence in support of either theory, and for this reason any new description of a possible glacial clast found at or near the stone monument is of potentially great importance. A small bullet-shaped boulder of welded tuff was found in a Stonehenge excavation in 1924, and apart from a brief examination by geologists from the Institute of Geological Sciences (IGS) around 1970, it has been stored out of sight and out of mind. Its geological source is uncertain. Following a detailed examination of its shape and surface characteristics it is now proposed that it has been subjected to glacial transport and that it has had a long and complex history. It is also proposed that the abundant weathered and abraded bluestone boulders and slabs at Stonehenge were also glacially transported, along with many of the cobbles and stone fragments found in the sediments of the local landscape. The elaborate archaeological narrative of bluestone quarrying and human transport to Stonehenge must now be re-examined. Kurzfassung: Über die Frage wie die sogenannten "Bluestones" von Ihren zahlreichen Quellen im Westen von Wales zu ihren heutigen Fundorten in und um Stonehenge transportiert wurden, gibt es ehebliche Differenzen. Seit einem Jahrhundert gehen die meisten Archäologen davon aus, dass die Steine von Menschen transportiert wurden, allerdings sind viele Geowissenschaftler der Meinung, dass die Steine mittels glazialen Transportes die "Salisbury-Plain" erreicht haben. Für beide Theorien gibt es bemerkenswert wenige Beweise. Deshalb ist jede neue Beschreibung eines möglichen glazialen Geschiebes, das am oder in der Nähe des Steinmonuments gefunden wurde, von potenziell großer Bedeutung. Ein kleiner, geschossartig geformter Block aus verschweißtem Tuffstein wurde 1942 bei einer Ausgrabung in Stonehenge gefunden und abgesehen von einer kurzen Untersuchung durch Geologen des UK Institute of Geological Sciences (IGS) um 1970, wurde er aus den Augen und aus dem Sinn eingelagert. Seine geologische Herkunft ist ungewiss. Nach einer eingehenden Untersuchung seiner Form und Oberflächenbeschaffenheit wird nun angenommen, dass er glazial transportiert wurde und eine lange und komplexe Geschichte hinter sich hat. Es wird weiterhin vorgeschlagen, dass die zahlreichen verwitterten und abradierten "Bluestone"-Blöcke und -Platten, ebenso wie viele der Feldsteine und Steinfragmente, die in den Sedimenten der Landschaft um Stonehenge auftreten, ebenfalls glazial transportiert wurden. Das ausgefeilte archäologische Narrativ des "Bluestone"-Abbaus und -Transports durch den Menschen nach Stonehenge muss nun neu untersucht werden. (Abstract was translated by Christopher Luethgens.) [ABSTRACT FROM AUTHOR]

Thermochronological data are essential to constrain thermal and exhumation histories in active mountain ranges. In the Central Andes, bedrock outcrops are rare, being blanketed by widespread late Palaeogene–Neogene and younger volcanic formations. For this reason, the exhumation history of the Western Cordillera (WC) in the Peruvian Andes has only been investigated locally along the mountain range. Dense thermochronological data are only available in canyons of the Arequipa (16° S) and Cordillera Negra regions (10° S). We present new apatite (U‐Th)/He and fission‐track data from the 1 km deep Cañete Canyon (13° S), where the Oligo‐Miocene deposits are preserved lying conformably on an Eocene palaeo‐topographic surface. Thermal modelling of thermochronological data indicate that the 30–20 Ma ignimbrite deposits overlying the bedrock were thick enough to cause burial reheating. We demonstrate that burial associated with thick volcanic formations should be taken into account when interpreting thermochronological data from the WC or in similar volcanic‐arc settings. [ABSTRACT FROM AUTHOR]

Mandro in Sahibganj District of Jharkhand State, India is known for its abundance of petrified wood and floral impressions from the Rajmahal Traps of Albian-Aptian age. This locality is among the 34 Geological Heritage Sites identified by the Geological Survey of India. The scientific importance of the site is vested in the intricate preservation of petrified wood and floral impressions in a single locality. The plants were transported by pyroclastic volcanic activity, and the tuff and crystal-laden pumice helped preserve the fossils, including upright tree stumps with intact root systems. Such an association of floral fossils with ignimbrite is of high scientific relevance and is one of its kind in India. At present, the Geoheritage Site, Mandro is compromised by the lack of legislative provisions guiding conservation of the site. Our study highlights bottlenecks in the development of the Geoheritage Site and suggests the formulation of an integrated-sustainable tourism circuit combining natural, anthropological, cultural and historical touristic components. We advocate operating the circuit through community participation, ensuring trust and capacity building among the local People. The circuit is an exclusively local tourism engine that could address socioeconomic disparities while developing as a hub for research and innovation across different disciplines. Paramount to these efforts is attaining Sustainable Development Goals and global recognition for the Geoheritage Site and the Circuit. [ABSTRACT FROM AUTHOR]

The aim of this research work is to study the effect of salt mist ageing on the physico-mechanical properties of two ignimbrites from the Canary Islands (Spain). Due to their insular nature and extensive coastlines, these regions are highly susceptible to atmospheric salt aerosols, which is a significant weathering agent for building materials. The ignimbrites analysed are marketed under the names "Azul Lomo Tomás de León" and "Marrón de Abades" and are widely used as building stones. Petrographic, mineralogical and chemical properties were obtained via polarisation microscopy, X-ray diffraction and X-ray fluorescence. The samples were subjected to 60 cycles of a salt mist environment, following relevant European standards. Scanning electron microscopy images of the specimens were analysed along with physical properties, including apparent density, open porosity, water absorption, colourimetry and ultrasound propagation velocity, initially and after every 20 cycles, allowing us to assess their evolution during the ageing test. Mechanical properties were evaluated using uniaxial compressive strength and flexural strength under concentrated load tests on two groups of specimens: one unaged and the other subjected to 60 ageing cycles. With the exception of apparent density, the other properties show a decrease between 5% and 30%. However, open porosity increases and is one of the properties most affected by the ageing test. [ABSTRACT FROM AUTHOR]

The Novohrad–Nógrád UNESCO Global Geopark is the first cross-border geopark located between Slovakia and Hungary, Eastern–Central Europe. “Ancient world without borders” – its motto reflects both the remarkable geodiversity and the strong link between people living on either side of the state border. In this relatively small area, almost all types of eruption products can be found from basaltic through andesitic to rhyolitic, reflecting the wide-ranging volcanism of the Pannonian Basin over the last 20 million years, which were the largest eruptions in Europe at the time. The Ipolytarnóc Site, the gateway of the geopark and possessor of a European- Diploma for Protected Areas, documents when one of these devastating eruption events buried a subtropical-forested area with thick pyroclastic deposits and preserved vertebrate footprints. On the other hand, relatively young eruptions of basaltic magmas occurred in this area that give another specific atmosphere to the geopark. Columnar jointing with concave and convex curvilinear shapes shown both by basalts and andesites is another peculiar natural value. Due to the regional uplift and the associated erosion, most of the volcanic edifices were removed and the root zones of the volcanoes were revealed, giving a special character. The volcanic heritage meets specific cultural and historical heritage, which makes this geopark a particular tourist destination. There are four visitor centers and several nature trails with explanation panels showing concise summaries of the volcanological features in three languages (Hungarian, Slovakian and English). Among the rich indoor and outdoor activities, the annual Volcano Day program in Ipolytarnóc with an interactive volcano show attracts many people. This is an evolving geopark, where continuously renewing attractions serve the geoeducation and geotourism purposes in parallel with geoheritage conservation management.

A multiphase fluid dynamic model is used to explore the effects of entrainment of granular debris into sustained volcanic jets such as those which produce sub-Plinian to Plinian eruption columns. The debris may be sourced from processes such as avalanches from crater walls or from recycling of previously erupted material. The results indicate that debris is not immediately, homogeneously mixed into a jet but instead forms a dense sheath that is dragged upward around the jet margin. While very small volumes of debris relative to the eruptive discharge rate mix progressively into the jet with increasing altitude, the dense sheath can inhibit entrainment of air into the lower portions of the jet, which may explain signs of column instability such as increased stratification in fallout deposits where lithic content increases. As debris volume increases, the dense sheath can collapse from a range of elevations to feed pyroclastic currents. The presence of the sheath of entrained debris contradicts some assumptions such as the top-hat profile for density and velocity that is commonly used in 1-D models. Transitions from fallout-producing buoyant column to collapsing behavior can be related to debris entrainment without any changes in primary eruption parameters such as vent size, exit velocity, or gas content. Boiling-over behavior can also be caused by debris entrainment, including recycling of previously erupted material such as might occur in a crater with restricted outlet. When entrained debris is relatively fine-grained such that it can couple well with the erupting mixture, complex, highly transient overpressured jet processes can occur due to the pinching effect of debris flowing into the base of the jet. Increasingly coarse debris causes collimation of the jet within the sheath of entrained material. The results suggest that accounting for the effects of debris entrainment is likely important for theoretical assessment of many natural eruption sequences and for assessment of hazard scenarios for potential sub-Plinian to Plinian activity. [ABSTRACT FROM AUTHOR]

Subaqueous eruptions alter the chemical conditions of the lake by intensifying the interaction between hot volcanic rocks and water, resulting in the exchange of alkalis. The lower part of the Fengcheng Formation in the Mahu Sag, NW China, has abundant rhyolitic welded tuff and related pyroclastic deposits, which were deposited under ancient alkaline lacustrine deposits of the Fengcheng Formation. Despite this, the effect of the eruption process on the formation of the alkali lake remains unclear. To gain a better understanding of the eruptive behaviour and emplacement processes, detailed drilling core descriptions, microscopic observations, and interpretations of textural characteristics of rhyolitic welded tuff units and adjacent volcano‐sedimentary associations have been conducted. The rhyolitic welded tuff can be categorized into seven lithofacies units based on the degree of welding, devitrification characteristics, pore development, and filling characteristics. The age of eruption was determined through zircon U–Pb dating of the rhyolitic welded tuff, revealing it to be approximately 300 Ma, thereby providing constraints on the deposition time of alkaline lacustrine deposits. Mudstones that encase the welded tuff unit and quenched structures such as perlitic fractures, quench cracks of spherulite and lithophysae, and chalcedony spherules indicate that the welded tuff unit was formed through subaqueous eruption. Alkali fractionation (sodium and potassium) occurs in the spherulite and lithophysae zone and at the top condensation boundary, demonstrating that the subaqueous eruption process significantly enhanced devitrification and hydration, causing sodium to escape from the welded tuff and released into the lake water as sodium ions. The rhyolitic welded tuff provides evidence of the evolution of a subaqueous felsic eruption where the water‐rock reaction played a fundamental role in alkalizing the lake by providing the lake with sodium ions in Mahu Sag. [ABSTRACT FROM AUTHOR]

The study area of Rodafnidia on the island of Lesbos (Greece) is considered of archaeological interest, as Paleolithic stone tools have been recovered through excavation and collected from the ground surface in recent years. Geologically, the area is mostly covered by Quaternary post-alpine deposits and volcanic rocks. This paper presents the application of a local geophysical survey to determine the volume of the upper Quaternary deposits in which the Paleolithic artefacts can be found and the identification of their ignimbrite substrates. For this reason, the geoelectrical method was selected as the most appropriate for determining the lithostratigraphic subsurface layers. More specifically, a grid of twenty-one (21) Vertical Electrical Soundings (VES) along with an Electrical Resistivity Tomography (ERT) was carried out. The interpretation of the results of these surveys, in conjunction with the results of older excavation trenches, revealed that the Quaternary deposits have been investigated at depths ranging from 0.5 up to 28.5 meters. Furthermore, the lithological boundary of these post-alpine deposits and their underlying pyroclastic ignimbrite flow (with resistivity 24.0–58.0 Ohm.m) seem to dip to the north. The volume of the Quaternary layer is proposed as the maximum depth for archaeological investigation with high chances to recover more Paleolithic material. [ABSTRACT FROM AUTHOR]

Fairy chimneys of ignimbrite are well studied in Cappadocia in central Anatolia, Turkey. The ignimbrite landforms of Arizona's Basin and Range, USA, in contrast, remain relatively unexplored in geomorphic scholarship, despite decades of geological research on the characteristics of the ignimbrites themselves. This research focuses on the rock‐decay processes that modify Arizona's Basin and Range fair chimneys. Dissolution of glass and groundmass, measured along joints using digital image processing of back‐scattered electron microscope imagery, reveal a 3× higher porosity than inside the rock interior. This method also measured a 3‐4× increase in dissolution near the base of the chimney compared with the rock interior, leading to notch development that promotes chimney mass wasting and subsequent ballistic impacts. Epilithic organisms studied with electron microscopy both enhance rock decay and promote case hardening. These observations are consistent with prior understanding of how fairy chimneys evolve over time: columnar joints exposed on cliff faces experience enough decay to allow erosion of joint material, this erosion separates the chimney from the rock face and notch development near the chimney base promotes mass wasting. The rock‐decay processes studied here likely operate on very different timescales. Mass wasting events leading to ballistic impacts occur at observable timescales. Varnish microlamination dating, using ultrathin sections of rock varnish formed on fairy chimneys, indicates that the case hardening of the top of fairy chimneys are much more stable than the sides; the tops last experienced surface detachment during the early Holocene, as opposed to the sides that experienced flaking throughout the late Holocene. The timescale of basal notch development is not known, with the exception that the very surface of notches erode at rates too fast to accumulate rock varnish. The timescales of epilithic organisms enhancing rock decay and dissolution of columnar joints are not known. [ABSTRACT FROM AUTHOR]