Volcanic Ash Deposits Research Articles

U-Pb dating of pedogenic calcite near the Permian−Triassic boundary, Karoo Basin, South Africa

We report U-Pb age determinations of carbonate nodules from an in situ paleosol horizon in the Upper Permian Balfour Formation and from several horizons of pedogenic nodule conglomerate (PNC) in the Triassic Katberg Formation, Karoo Basin, South Africa, using laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS). The paleosol sample yields an age of 252 ± 3 Ma, which overlaps with a previous high-precision U-Pb zircon date from a volcanic ash deposit 2 m above the paleosol. This relationship demonstrates the reliability of using LA-ICP-MS dating techniques on terrestrial pedogenic calcite. Two PNC samples collected at the base of the Katberg Formation within the same sandstone unit yield ages of 255 ± 3 Ma and 251 ± 3 Ma. The age of 251 ± 3 Ma overlaps with the high-precision U-Pb zircon date below the PNC and is a maximum age estimate of deposition for the base of the Katberg Formation. Our results show that reworked nodules in the same concentrated conglomerate lag can be of different ages, but that similarly aged nodules are spatially associated. In addition, two PNC samples collected higher in the section yield ages of 249 ± 3 Ma and 241 ± 3 Ma, providing maximum depositional ages for the lower to middle Katberg Formation for the first time. We demonstrate that pedogenic carbonate nodules can be dated with meaningful precision, providing another mechanism for constraining the age of sedimentary sequences and studying events associated with the Permian−Triassic transition in the central Karoo Basin, even though the extinction boundary may not be preserved in this area.

Tree diversity and social–ecological resilience of agroforestry after volcanic ash deposition in Indonesia

Smallholder farmers and their agroecosystems in active volcanic landscapes need to deal with and recover from eruptions. Resilience to extreme shocks may increase with system diversity, enhancing food and income security and ecosystem services provision; however, the longer term effects of volcanic ash are rarely assessed. To test the hypothesis that tree diversity contributes to the social–ecological resilience of coffee-based agroforestry, we quantified (1) the immediate effects of deposition of a 15-cm ash layer on tree survival, (2) the effect of volcanic ash on aboveground C stocks, tree diversity and wood density frequencies, (3) litter layer dynamics, and (4) farming system and income recovery 3 years after. Observations in four land-use systems before and after ash deposition (remnant forest, coffee-based complex and simple agroforestry, annual crops) were complemented by 46 farmer interviews on tree species’ survival, system, and financial recovery. Based on farmer interviews, low-wood-density trees were most affected by volcanic ash deposition. Ash deposition did not, after 3 years and across land-use systems, significantly change tree density, basal area, or C stocks. In contrast, species richness in coffee-based agroforestry increased significantly. Standing litter stocks in agroforestry decreased, but slower decomposition partially compensated for reduced litter input. Farmers stated that diversity and flexibility in coffee-based agroforestry support a system recovery that is faster than that for annual crops, suppressing income fluctuation. Farmer’s adaptive responses to enhance species diversity contributed to the resilience of farms, by retaining basic system structure and functions of agroforestry, and increasing product diversity and income.Graphical abstract

Change assessment of the Tonga island surface temperature before and after volcanic eruption based on FY-3D time series dataset

Taking advantage of the 250 m resolution and daily observation of dual thermal infrared channels data of the Medium Resolution Spectral Imager (MERSI) onboard the Fengyun 3D (FY-3D) satellite, a refined thermal infrared island surface temperature (ILST) inversion model is established through radiation transmission simulation. And the Tonga ILST change maps before and after the volcanic eruption are produced and analyzed based on ILST time series dataset. The results show that the ILST decreases by 2 K –3 K within the five days after the eruption due to the amount of volcanic ash deposition, but increases significantly by 2 K –6 K within the fifth to tenth days after the eruption. The trend of time-limited cooling, warming, and then gradual recovery after volcanic eruption is very obvious. Through the manual cleaning and the scouring by seawater or rainwater to the volcanic ash covered ground, more parts of the island surface restored its original state. Hence, the Tonga ILST also increased gradually within a week thereafter. However, in regions with local vegetation, the recovery time of ILST would be longer. The temporal and spatial resolution of FY-3D MERSI meets the need for monitoring the changes of the island surface states before and after the volcanic eruption.

Volcanic ash from La Palma (Canary Islands, Spain) as Portland cement constituent

The last volcanic eruption on the island of La Palma (Spain) took place in 2021. Significant activity started in September of that year with the vigorous emission of volcanic gases and ash and lasted for three months. It is estimated that the Cumbre Vieja volcano emitted more than ten million cubic meters of ash comprising pyroclastic materials like those found in many parts of the world. Some of these volcanic ash deposits are untapped, despite their potential construction industry applications. Since the chemical composition and mineralogy of the ash depends on the type of magma from it originates, this paper characterizes this material and evaluates its suitability as a major constituent of Portland cement. This volcanic ash is rich in silica (45%) and alumina (15%), meaning it reacts with portlandite. The blended cements with up to 40% replacement content meet the standardized chemical, physical, and mechanical requirements and present good intrinsic durability values (resistivity and capillary absorption), making them viable for the manufacture of low-carbon-footprint eco-cements. This paper seeks to provide society with lasting technical, environmental, and social benefits through recovery of this ash.

The impact of volcanic ash deposition and the Storegga Slide on organic carbon preservation processes in marine sediments near Iceland

The burial of organic carbon (OC) in marine sediments is a considerable sink for carbon, removing OC from the active ocean-atmosphere system. Both the total OC buried, and the proportion of OC retained in sediments after burial, varies by location, with some areas of the ocean floor known to be ‘hotspots’ of OC sequestration. Two potential such hotspots may be sediments containing high proportions of tephra (the unconsolidated products of explosive volcanism), and locations of turbidite deposition, but knowledge of specific burial regimes in such locations remains poorly constrained. To fully investigate these processes, we performed a holistic (organic and inorganic) geochemical analysis of samples from the Aegir Ridge, which contain both tephra layers and material from the Storegga Slide, a large turbidite. We show sediments found between the Storegga Slide and the tephra are a location of high OC preservation, linked to reducing conditions caused by the rapidly deposited slide layer sealing the sediments from overlying water column O2. We see little evidence for tephra positively affecting OC preservation at our site, but this is likely a feature of specific burial conditions, with the responsible mechanisms depending highly on the nature of the tephra. Our findings demonstrate how even in locations proposed as OC burial hotpots, the processes controlling this burial are highly complex, and that levels of sedimentary OC burial must be assessed on a case-by-case basis.

Late Pleistocene human occupations in the southern puna, Chile (12,4–10,7 ka cal. BP): Primary results from the Salar de Infieles (25°S, 3529 m. a.s.l.)

This article presents the results of excavations at the Infieles-1 site, located at 3529 m. a.s.l. in the Salar de Infieles (25°S), highlands of the Chile's southern Puna ecoregion. An initial human occupation was discovered next to an ignimbrite rock-shelter at a depth of 70–80 cm on top of a volcanic ash deposit, dated between 10,798 and 12,440 cal yr BP. The archaeological record consists of lithic wasted-flakes and knapping debris, an ultra-marginal andesite side-scraper, vicuña bone fragments and traces of red mineral pigment. As far as now, this event is the first human occupation recorded in the southern Puna. It is a camp associated with more favourable environmental conditions during the late Central Andean Pluvial Event II (CAPE II).

Predicting the extent of andic soils across western Haleakalā, Maui

AbstractMaui is one of five Hawaiian Islands affected by orographic climate effect, exhibiting a massive precipitation gradient across western Haleakalā. However, high variability of volcanic ash deposits as a parent material across the study area complicates the ability to isolate the influence of climate on soil formation. Little is documented about the spatial extent of ash deposition, frequency and intensity of volcanic ejecta events, and composition of ash. Therefore, andic soils, which contain short range order (SRO) aluminosilicates and iron oxides that result in unique soil chemical and physical properties, are challenging to map. Using environmental and andic property data from 16 pedons sampled in the study area—bulk density, phosphate retention, and aluminum plus ½ iron extracted by ammonium oxalate—we applied multiple linear regression to create spatial prediction models of these three soil properties. Predicted soil properties were then used to classify andic soils. The mean prediction for an independent set of pedons showed a soil classification accuracy of 50% in the study area for Andisols (data to 60 cm), andic intergrades (data to 75 cm), and non‐andic soils. Soil property predictions using depth‐weighted average data to 1 m increased soil classification user accuracy of Andisols to 87.5%, andic‐intergrades to 100%, and non‐andic soils to 83.3%. Whether a soil exhibits andic soil properties within 60 or 75 cm is irrelevant when considering prior or current presence of ash in a soil. Accounting for all available pedon data with depth proves most important when attempting to predict andic properties and classes.

Effect of elevation and slope orientation on pedogenesis of late Holocene volcanic ash on a tropical high mountain in central Mexico

The influence of climate on pedogenesis is elevation dependent, but little is known on the influence of slope orientation. This investigation focuses on the development of soils formed on Holocene (1100 and 5600 years old) volcanic ash deposits along an elevation gradient from 3000 to 4300 m a.s.l. on a high mountain in central Mexico. Soil profiles were analyzed on both N- and S-facing slopes at 3000, 3400, 3800, 4000 and 4300 m a.s.l. To determine the effect of climate (dependent on elevation and slope orientation) on pedogenetic processes, other factors such as age and type of parent material, landform position, and slope angle were kept constant. Soil temperature was recorded at 10 cm depth at each site for one year. Significant differences in temperature were found along the elevation gradient and between N-facing and S-facing slopes. Selective extractions of Fe, Al, and Si (using dithionite, oxalate, and pyrophosphate) indicate vitric properties on the 1100-year-old tephra (modern soil) throughout the elevation gradient, while the soil formed on the 5600-year-old tephra (buried by the 1100 year-old tephra) shows andic properties. The orientation of slopes has favored two evolutionary trajectories in the 1100-year-old soil: short-range-order minerals dominate on S-facing slopes, and organo-metallic complexes on N-facing slopes. The lower preservation of ash and pumice layers on S-facing slopes suggests that they have experienced geomorphic instability at centennial scales. The pedogenetic and stratigraphic differences observed between N- and S-facing slopes can be extrapolated to similar valleys and volcanic mountains.

Wind Tunnel Experiments on Volcaniclastic Dust Emission and Dispersion Initiated by Water Droplet Impact

AbstractIceland contains active dust regions within high‐latitude, cold‐climate environments. An abundant supply of particulates <10 μm in diameter (PM10) is available within its extensive glacial outwash plains and through widespread transport and deposition of volcanic ash with hydrophobic tendencies. The climate is notably wetter than dust regions located in hot deserts, so that additional processes governing dust emission must be considered, inclusive of rain splash. Field workers in Iceland report that dust emission events sometimes overlap with precipitation. This study used high‐speed photography in wind tunnel experiments to assess the influence of water droplet impact and wind shear on the detachment and suspension of particulates collected from several active dust source regions within Iceland. Concentrations of PM10 sampled downwind of a single water droplet impact reached values as high as 104 μg m−3 and were positively correlated with increasing wind speed, droplet impact velocity and angle. Our measurements demonstrate that wind shear in a turbulent flow is important for the dispersion of aerosols ejected via water droplet impact from the surface of dry sediment, and that these coincident mechanisms can be highly effective agents of erosion, especially in light winds that are normally incapable of dust entrainment. Foremost, this study provides further evidence of the complexity of dust emission in cold environments and the importance of examining this phenomenon over a wide range of temporal and spatial scale.

Water repellency by volcanic ash interacting with organic matter: Incubation response and effect on infiltration

Volcanic ash deposition disrupts soil surface hydrology. Our previous study showed that soil infiltration was reduced eightfold after a volcanic eruption in various land-use systems adjacent to Mount Kelud (Indonesia). Yet, soil macroporosity was relatively unchanged, indicating soil hydrophobicity. We tested the hypothesis that hydrophobicity or water repellency (WR) can be induced by volcanic ash interacting with organic matter and quantified its effect on surface water infiltration.We combined volcanic ash with leaf litter from coffee, durian, pine and mixed sources and tested for WR as a function of incubation time (0–16 weeks) and soil water content (θ, %), with Water Drop Penetration Time (WDPT, s) and Contact Angle (CA, o) as WR metrics. Lipids content (%) and pH were also analysed during incubation. Water droplets were placed onto a material tested for WR in a slope-adjustable stage to determine the critical angle for droplet runoff before penetration. Finally, to quantify the effect of WR on water flow, we layered 5 and 10 cm of ash with organic matter additions on top of a control soil column and performed infiltration (hydraulic conductivity) measurements.Among litter sources, pine litter induced the highest WR. There were significant relationships between WR, lipid, and pH. However, these relationships became weaker with material water contents > 7%. A significant relationship was also found between CA and critical slope of both small and large drops. A higher CA lowered the minimum critical slope for droplet runoff to 7° and 10° for the diameters of large and small water droplets, respectively. The mixture of volcanic ash and organic matter layered into the soil surface resulted in a five-times lower average hydraulic conductivity, with indications of air entrapment limiting water infiltration in a thicker ash layer. A higher CA was strongly associated with a lower hydraulic conductivity ratio, particularly under the 5 cm organic matter treatment. The WR effects on hydraulic conductivity are equivalent to at least a ten-fold reduction in effective soil porosity. By reducing infiltration, WR may contribute to ash movement in the volcanic landscape.

Application of a temporal decorrelation model using Sentinel-1 SAR data to Detect volcanic ash deposits related to the 2020 Taal volcano eruption

Volcanic ash deposits affect buildings, vegetation, and population. After a volcanic eruption, it is critical to detect the areas affected by ash deposits to achieve an advisable management of the emergency. Optical sensors have been widely used to carry out this task, but they are limited by solar illumination and weather conditions. As an alternative, Synthetic Aperture Radar (SAR) data are not affected by those limitations. Recently, a Temporal Decorrelation Model (TDM) that uses SAR data was proposed for detecting and mapping ash deposits, but it has only been applied to L-band data. Today there is available a huge quantity of C-band data acquired by the Sentinel-1 constellation. In this study we applied the TDM to Sentinel-1 data in order to assess its performance for detecting volcanic ash deposits after an eruption. We selected the eruption of Taal volcano in The Philippines on January 12, 2020, as our case study. We computed more than 4000 interferometric pairs from a dataset of 93 images acquired before, during, and after the eruption. Our results show that TDM can be applied to C-band data, despite the higher temporal decorrelation suffered by them. Our final probability map is consistent with the field evidence reported by the Philippines Institute of Volcanology and Seismology (PHILVOLCS) and the isopachs map reported in the literature. This new application provides a novel framework for the coherence exploitation of C-Band data. Also, this approach could be applied to detection and monitoring of other natural disasters.

Differential response of chlorophyll-a concentrations to explosive volcanism in the western South Pacific

When it is deposited in the ocean, volcanic ash has the potential to release iron and other nutrients into surface water to stimulate ocean productivity. In the western South Pacific Ocean (SPO), one of the most important volcanic ash deposition regions, occasional widespread transport of volcanic ash may supply the nutrients not only locally around source islands but also within the wider the western SPO, accompanied by phytoplankton response. Through a comparative analysis of satellite and reanalysis data for the past 19 years (2004–2022), this study reveals that four explosive volcanic eruptions, Rabaul volcano, Papua New Guinea (October, 2006), Ambae volcano, Vanuatu (July, 2018), Ulawun volcano, Papua New Guinea (June, 2019), and Hunga volcano, Tonga (January, 2022), had the most strong stratospheric injection (>15 km) and mass loading of volcanic materials over the wider the western SPO (covering an area of >765,000 km2). The transport of 2006, 2018, 2019 volcanic emissions, was not likely associated with significant ash deposition over the western SPO. However, the Hunga eruption led to the deposition of ash-laden volcanic plumes over a wide area (~2,000 km from source), and was followed by the increase in chlorophyll-a concentrations (Chl-a) in the region (~70% increase). Minor changes related to other nutrient sources (e.g., hydrothermal input) suggest a link between the increase in Chl-a and 2022 Hunga ash falls over the western SPO. Our results indicate that volcanic ash deposition has implications for phytoplankton productivity in the western SPO, and highlights the need for further research into understanding how nutrient supply alleviated limitations of phytoplankton at the community level.

A Carboniferous apex for the late Paleozoic icehouse

Abstract Icehouse climate systems occur across an abbreviated portion of Earth history, constituting c. 25% of the Phanerozoic record. The Late Paleozoic Ice Age (LPIA) was the most extreme and longest lasting glaciation of the Phanerozoic and is characterized by periods of acute continental-scale glaciation, separated by periods of ice minima or ice-free conditions on the order of <10 6 years. The late Paleozoic glaciogenic record of the Paraná and Kalahari basins of southern Gondwana form one of the largest, best-preserved and well-calibrated records of this glaciation. In the Carboniferous, the eastern and southern margins of the Paraná Basin and the Kalahari Basin were characterized by subglacial conditions, with evidence for continental and upland glaciers. In the latest Carboniferous, these basins transitioned from subglacial reservoirs to ice-free or ‘ice distal‘ conditions evidenced by the widespread deposition of marine deposits juxtaposed on subglacial bedforms. High-precision U–Pb zircon chemical abrasion thermal ionization mass spectrometry geochronological constraints from volcanic ash deposits in the deglacial marine black shales of the Kalahari Basin and from fluvial and coal successions, which overlie marine deposits in the Paraná Basin, indicate subglacial evidence in these regions is constrained to the Carboniferous. The loss of ice in these regions is congruent with a late Carboniferous peak in p CO 2 and widespread marine anoxia in the late Carboniferous. The permeant retreat of glaciers in basinal settings, despite an early Permian p CO 2 nadir, highlights the influence of short-term perturbations on the longer-term CO 2 record and suggests an ice threshold had been crossed in the latest Carboniferous. A definitive driver for greenhouse gases in the LPIA, such as abundant and sustained volcanic activity or an increased biological pump driven by ocean fertilization, is unresolved for this period. Lastly, the proposed Carboniferous apex for the high-latitude LPIA record is incongruent with observations from the low-latitude tropics where an early Permian peak is proposed.

Spatial and Temporal Quantification of Subaerial Volcanism From 1980 to 2019: Solid Products, Masses, and Average Eruptive Rates

AbstractVolcanism is one of the main mechanisms transferring mass and energy between the interior of the Earth and the Earth's surface. However, the global mass flux of lava, volcanic ash and explosive pyroclastic deposits is not well constrained. Here we review published estimates of the mass of the erupted products from 1980 to 2019 by a global compilation. We identified 1,064 magmatic eruptions that occurred between 1980 and 2019 from the Smithsonian Global Volcanism Program database. For each eruption, we reported both the total erupted mass and its partitioning into the different volcanic products. Using this data set, we quantified the temporal and spatial evolution of subaerial volcanism and its products from 1980 to 2019 at a global and regional scale. The mass of magma erupted in each analyzed decade ranged from 1.1–4.9 × 1013 kg. Lava is the main subaerial erupted product representing ∼57% of the total erupted mass of magma. The products related to the biggest eruptions (Magnitude ≥6), with long recurrence times, can temporarily make explosive products more abundant than lava (e.g., decade 1990–1999). Twenty‐three volcanoes produced ∼72% of the total mass, while two different sets of 15 volcanoes erupted >70% of the total mass of either effusive or explosive products. At a global scale, the 10 and 40‐year average eruptive rates calculated from 1980 to 2019 have the same magnitude as the long‐term average eruptive rates (from thousand to millions of years), because in both cases rates are scaled for times comparable to the recurrence time of the biggest eruptions occurred.

Cenozoic Exhumation and Deformation of the Intermontane Pastos Chicos Basin in the Southern Central Andes: Implications for the Tectonic Evolution of the Andean Plateau (Puna) and the Eastern Cordillera Between 23° and 24°S, NW Argentina

AbstractThe Andean Plateau of north‐western Argentina (Puna) at a mean elevation of ca. 4.2 km constitutes the southern continuation of the Altiplano; it is a compressional basin‐and‐range province comprising fault‐bounded, high‐elevation mountain ranges and largely internally drained basins with often thick sedimentary and volcaniclastic fill. Growing sedimentological and structural evidence supports the notion that the north‐western Argentine Andes between 22° and 26°S developed from an initial extensive broken‐foreland system that extended across the present‐day eastern Andean flank during the early to middle Eocene. However, compelling evidence of the tectonic history of this region is still missing. Here, we present new apatite fission track and zircon (U–Th)/He thermochronological data and U–Pb zircon ages from intercalated volcanic ash deposits from the Pastos Chicos Basin (23.5°S, 66.5°W) to constrain basin formation and the timing of major crustal deformation in the northern Puna. Inverse thermal modeling of the thermochronological data provides further temporal constraints on the late Cenozoic cooling history of the crust in this region and, by inference, on the timing of upper‐crustal shortening, range uplift, and basin formation in the northern sector of the present‐day Puna Plateau. Specifically, we argue for plateau‐wide distributed deformation in the Eocene between 23° and 24°S, followed by spatially disparate and diachronous deformation (Oligocene to Pliocene).

Ostracod and Foraminifer Responses to Late Pleistocene–Holocene Volcanic Activity in Northern Victoria Land as Recorded in Ross Sea (Antarctica) Marine Sediments

The impacts on ostracods and foraminifers caused by three Late Quaternary ashfalls of different intensities and recovered in the ANTA02-NW2 core sediments (Drygalski Basin, western Ross Sea) were analysed for the first time. Albeit with different timing, both associations demonstrated similar response patterns associated with the deposition of material from volcanic eruptions. In particular, based on the palaeontological evidence, it was possible to divide the cores into four intervals/phases recording the evolution of the ecosystem before and after the deposition events: (1) Pre-extinction phase (high abundance and high diversity values). (2) Extinction phase, characterised by the complete disappearance of ostracod fauna; the foraminiferal assemblage, although not entirely absent, records extremely low values of abundance and diversity (survivor assemblage). (3) Recovery phase (increasing abundance and diversity values), characterised by the recolonisation of some opportunistic taxa; species such as Australicythere devexa and Australicythere polylyca dominate the ostracod assemblage. (4) Post-extinction phase (high abundance and high diversity values), with the return to an environmental equilibrium characterised by the colonisation of specialised taxa such as Argilloecia sp., Cytheropteron sp., Echinocythereis sp., and Hemicytherura spp. Our results may aid in the understanding of how communities (i.e., ostracods and foraminifers) recovered after the impact of direct deposits of volcanic ash into ocean waters. The mechanisms by which disappearance and/or mortality was induced are still not clear. The release of toxic metals during the reaction of the volcanic ash with seawater, the resulting chemical alteration in the seawater, and the change in pH, together with the possible suppression of planktonic organisms, may have caused the two main extinction phases recorded by the ANTA02-NW2 core sediments.

Predicting wind-driven spatial deposition through simulated color images using deep autoencoders

For centuries, scientists have observed nature to understand the laws that govern the physical world. The traditional process of turning observations into physical understanding is slow. Imperfect models are constructed and tested to explain relationships in data. Powerful new algorithms can enable computers to learn physics by observing images and videos. Inspired by this idea, instead of training machine learning models using physical quantities, we used images, that is, pixel information. For this work, and as a proof of concept, the physics of interest are wind-driven spatial patterns. These phenomena include features in Aeolian dunes and volcanic ash deposition, wildfire smoke, and air pollution plumes. We use computer model simulations of spatial deposition patterns to approximate images from a hypothetical imaging device whose outputs are red, green, and blue (RGB) color images with channel values ranging from 0 to 255. In this paper, we explore deep convolutional neural network-based autoencoders to exploit relationships in wind-driven spatial patterns, which commonly occur in geosciences, and reduce their dimensionality. Reducing the data dimension size with an encoder enables training deep, fully connected neural network models linking geographic and meteorological scalar input quantities to the encoded space. Once this is achieved, full spatial patterns are reconstructed using the decoder. We demonstrate this approach on images of spatial deposition from a pollution source, where the encoder compresses the dimensionality to 0.02% of the original size, and the full predictive model performance on test data achieves a normalized root mean squared error of 8%, a figure of merit in space of 94% and a precision-recall area under the curve of 0.93.

Sacred plant impressions from Somma-Vesuvius volcanic ash deposits: A medicinal garden in Late Antique Acerra (Naples, Campania, Italy)?

The AD 472 eruption of Somma-Vesuvius widely impacted the northern and eastern territory around the volcano, laying down a complex sequence of pyroclastic fallout and pyroclastic current deposits. During archaeological test excavations conducted in the Acerra locality, Pollena eruption (AD 472) fallout and lahar deposits composed of fine ash containing traces of plant impressions were found. These deposits were sampled and carefully fractured in order to recover the plant imprints. Features of the ash impressions were compared with those of live plants and dried Herbarium specimens. Species identification was based on the characteristics of leaves (maximum width, type of leaf margin, size of midrib, angle of formation of the secondary veins) and fruits. Impressions of Mandragora officinarum L., Rosa canina L. and Hedera helix L. were recognized. This is the first documented discovery of subfossil mandrake specimens. The use of mandrake plants for healing and psychotropic purposes is referred to by Classical authors such as Pliny the Elder and Dioscorides; it was sometimes used mixed with rose. In addition, rose and ivy plants were symbolically important to the ancient Romans and were employed together as medicinal plants. The coexistence of these plants in a restricted area suggests the presence of a garden dedicated to sacred/medicinal plants. In addition, it is interesting to note that the discovery of mandrake plants with fruits supports the hypothesis that the eruptive event took place between the end of summer and the autumn.

Clay mineralogy mediated by pH and chemical weathering intensity of Permian–Triassic boundary K-bentonites at Dongpan (Guangxi, South China)

Volcanic ash deposits of the Permian-Triassic (P-T) transition in South China, in addition to being associated with the Permian-Triassic boundary mass extinction, are useful marker beds for regional correlation of sedimentary strata. This study investigates the source(s) of P-T volcanic ash layers in South China by studying their clay mineralogy and geochemical characteristics in deep-marine facies at Dongpan. Mineralogically, the Dongpan deposits consist mainly of clay minerals and quartz, with small amounts of anatase and feldspar. C lay minerals in the volcanic ash layer are mainly composed of R1 mixed-layer illite/smectite (I/S) (56.2–74.8%), smectite (14–22.8%), kaolinite (5.4–27.3%) and illite (1.2–5.3%). The relatively high content of kaolinite and weak illitization of smectite at Dongpan differ from the features of clay-mineral assemblages in other contemporaneous deep-water facies. Our results indicate that strong chemical weathering in an acidic and oxidizing environment characterized by low K+/H+ ratios inhibited uptake of K+ in the interlayers of I/S clay minerals and, thus, illitization of smectite. We infer that weathering intensity rather than redox state was the primary influence on the rate of kaolinization of clay minerals in these deep-marine facies. The Dongpan section exhibits a uniform REE pattern, indicating a single and stable source of volcanic ash during the P-T transition. Trace-element and REE distribution patterns and mixed-layer I/S clay-mineral morphologies are consistent with the source of the volcanic ash at Dongpan being a nearby continent-margin volcanism.

Long-term change of the eruption activities of Sakurajima volcano, Japan, inferred from the fallout tephra deposits

Stratigraphic analysis of fallout tephra deposits in and around a volcano provides a framework for understanding the long-term temporal change in the volcano’s activities. Here, we reconstruct the evolution of the volcanic activities of Sakurajima volcano based on reconstructed tephra stratigraphy by original field surveys, compilations of geological and archeological data, and new 14C dating. We define three eruption stages of Stage 1 (30–24 ka), Stage 2 (12.8–4.8 ka), and Stage 3 (4.5 ka–present), based on a major hiatus and shifting of the volcanic centers. Stages 2 and 3 are further subdivided according to the predominant mode of volcanic activity. Revised distribution of tephra deposits indicates that a total of 14.5 km3 (5.8 km3 dense rock equivalent) of fallout tephra has erupted from Sakurajima. Among them, Stage 2a (13–8 ka) produced the largest volume of tephra fallout deposits, suggesting that Sakurajima peaked in magma discharge during Stage 2a (2.9 km3/kyr) and then decreased rapidly toward Stage 2b (8–4.8 ka; 0.07 km3/kyr). The eruption of large-volume tephra deposits in Stage 2a, followed by the development of a thick volcanic ash layer in Stage 2b, indicates the eruption style shifted from explosive pumice eruptions in Stage 2a to ash-producing Vulcanian activity in Stage 2b, with decreasing magma discharge rate. Thick volcanic ash deposits covered by several fallout tephra deposits during Stage 3 also reflect a shift in activity from repeated Vulcanian explosions with lava effusions in Stage 3a (4.5–1.6 ka) to predominantly pumice eruptions during the historical period (Stage 3b) with an increasing magma discharge rate. The case study of Sakurajima presented here demonstrates that the combined analysis of the distribution, stratigraphy, and age of pumice fall layers with the lava and pyroclastic cone deposits on the volcanic edifice is a powerful tool for deciphering the growth history of complex stratovolcanoes.