Eruption Deposits Research Articles

A sulfur and halogen budget for the large magmatic system beneath Taupō volcano

The transport and degassing pathways of volatiles through large silicic magmatic systems are central to understanding geothermal fluid compositions, ore deposit genesis, and volcanic eruption dynamics and impacts. Here, we document sulfur (S), chlorine (Cl), and fluorine (F) concentrations in a range of host materials in eruptive deposits from Taupō volcano (New Zealand). Materials analysed are groundmass glass, silicic melt inclusions, and microphenocrystic apatite that equilibrated in shallow melt-dominant magma bodies; silicic melt and apatite inclusions within crystal cores inferred to be sourced from deeper crystal mush; and olivine-hosted basaltic melt inclusions from mafic enclaves that represent the most primitive feedstock magmas. Sulfur and halogen concentrations each follow distinct concentration pathways during magma differentiation in response to changing pressures, temperatures, oxygen fugacities, crystallising mineral phases, the effects of volatile saturation, and the presence of an aqueous fluid phase. Sulfur contents in the basaltic melt inclusions (~ 2000 ppm) are typical for arc-type magmas, but drop to near detection limits by dacitic compositions, reflecting pyrrhotite crystallisation at ~ 60 wt. % SiO2 during the onset of magnetite crystallisation. In contrast, Cl increases from ~ 500 ppm in basalts to ~ 2500 ppm in dacitic compositions, due to incompatibility in the crystallising phases. Fluorine contents are similar between mafic and silicic compositions (< 1200 ppm) and are primarily controlled by the onset of apatite and/or amphibole crystallisation and then destabilisation. Sulfur and Cl partition strongly into an aqueous fluid and/or vapour phase in the shallow silicic system. Sulfur contents in the rhyolite melts are low, yet the Oruanui supereruption is associated with a major sulfate peak in ice core records in Antarctica and Greenland, implying that excess S was derived from a pre-eruptive gas phase, mafic magma recharge, and/or disintegration of a hydrothermal system. We estimate that the 25.5 ka Oruanui eruption ejected > 130 Tg of S (390 Tg sulfate) and up to ~ 1800 Tg of Cl, with potentially global impacts on climate and stratospheric ozone.

Simultaneous fall and flow during pyroclastic eruptions: A novel proximal hybrid facies

Abstract The deposits of Plinian and subplinian eruptions provide critical insights into past volcanic events and inform numerical models that aim to mitigate against future hazards. However, pyroclastic deposits are often considered from either a fallout or pyroclastic density current (PDC) perspective, with little attention given to facies exhibiting characteristics of both processes. Such hybrid units may be created where fallout and PDCs act simultaneously, where a transitional phase between the two occurs, and/or due to reworking. This study presents analysis of a novel hybrid pyroclastic lithofacies found on Tenerife (Canary Islands) and Pantelleria (Italy). The coarse pumice block facies has an openwork texture and correlates with distal Plinian units, but it is cross-stratified and relatively poorly sorted with an erosional base. The facies is proposed to record the simultaneous interaction of very proximal fallout and turbulent PDCs, and it reveals a fuller spectrum of hybrid deposition than previously reported. This work highlights the importance of recognizing hybrid deposition both in the rock record and in hazard modeling.

Late Holocene Tephrostratigraphy at Chokai Volcano, Northern Japan, and Contribution to Hazard Assessment

History and pattern of explosive eruptions at Chokai volcano, Japan, in the last 2500 years were investigated from tephra survey and accelerator mass spectrometry (AMS) radiocarbon dating. The tephrostratigraphy was established based on observations at eight hand-dug trenches and three outcrops. The well-correlated tephra layers were dated at c. 2.5 ka, 2.1–1.9 ka, 1.8 ka, and 1.6 ka, indicating major eruptions occurred at these ages. The tephra from the documented 871 CE eruption was also identified. Componentry analysis of ash was carried out for these five eruption deposits. The changes in tephra facies and ash components within an unbroken series of tephra layers indicate a shift from hydrothermal-dominant phreatic or phreatomagmatic eruption to magma-dominant eruptions in a single episode. Common eruption sequences were identified based on the combination of tephra facies variation and records of witnessed eruptions. Every volcanic activity begins with precursory activity of seismicity, fumaroles, and snow melting for weeks to months, then onset hydrothermal-dominant eruption happens. Then, the eruption evolves to a magma-dominant eruption, or alternatively, the hydrothermal-dominant eruption persistently continues until cessation. The eruption sizes are VEI 2 or more minor. Lahar can occur at any stage of the eruption, resulting in damage to the residential area at the base of the volcano. The eruption patterns and the extent of hazard risks elucidated by this study will be utilized to hazard mitigation plans.

High-resolution Digital Surface Model of the 2021 eruption deposit of Cumbre Vieja volcano, La Palma, Spain

Identifying accurate topographic variations associated with volcanic eruptions plays a key role in obtaining information on eruptive parameters, volcano structure, input data for volcano processes modelling, and civil protection and recovery actions. The 2021 eruption of Cumbre Vieja volcano is the largest eruptive event in the recorded history for La Palma Island. Over the course of almost 3 months, the volcano produced profound morphological changes in the landscape affecting both the natural and the anthropic environment over an area of tens of km2. We present the results of a UAS (Unoccupied Aircraft System) survey consisting of >12,000 photographs coupled with Structure-from-Motion photogrammetry that allowed us to produce a very-high-resolution (0.2 m/pixel) Digital Surface Model (DSM). We characterised the surface topography of the newly formed volcanic landforms and produced an elevation difference map by differencing our survey and a pre-event surface, identifying morphological changes in detail. The present DSM, the first one with such a high resolution to our knowledge, represents a relevant contribution to both the scientific community and the local authorities.

A Petrologic Insight into Transitioning Eruption Styles from the Devil’s Rock Region, Ambae, Vanuatu

AbstractAmbae Island is the largest volcano in the New Hebrides Arc with recent eruptive activity occurring primarily at the summit and along the island’s rift zone. The Devil’s Rock area forms a prominent outcrop on the SW coast. Eruptive deposits here are derived from both strombolian and phreatomagmatic eruptions that contain a similar olivine- and clinopyroxene-rich juvenile basaltic component. This study focuses on a particular transition from strombolian to phreatomagmatic activity to understand if the change in eruption style is a function of magmatic processes or properties (e.g. different composition, ascent rate, degassing history) or if it is driven purely by external factors (e.g. magma–water interaction and/or vent migration). Melts from the strombolian to phreatomagmatic phase record the same melt compositions and volatile contents, suggesting the same magma batch is involved throughout the eruption. More broadly, similarities in H2O, CO2 and S concentrations between olivine- and pyroxene-hosted melt inclusions from Devil’s Rock melt inclusions and those erupted during the 2017–2018 summit eruptions may indicate that a long-term shared magmatic reservoir exists beneath Ambae. Physical characteristics of juvenile tephra including groundmass crystallinity and porosity are combined with melt inclusion compositions to better understand the degassing and crystallisation history and melt evolution of this volcanic system across the transitioning eruptive sequence. Groundmass crystallisation is variable and negatively correlated with connected porosity of erupted scoria reflecting mixing of materials at the vent and inclusion of dense clasts from conduit margins. A direct comparison of crystallinities between strombolian and phreatomagmatic phases reveals higher crystallinity in the strombolian deposits, which is reflective of post-fragmentation crystallisation of clasts. This is particularly evident in the proximal strombolian materials. Qualitative crystallisation textures of melt inclusions are used in a similar fashion to groundmass crystallinities to assess the relative timing of cooling. These trends mirror those of the groundmass and suggest longer cooling times and more effective degassing for samples of the transitional materials. Based on our analysis of deposits at Devil’s Rock, the transition from a strombolian to a phreatomagmatic eruption style was likely driven by groundwater or seawater incursion into the shallow conduit, close to modern-day sea level. Overall, these results suggest a dynamic system where different magmatic cooling histories for strombolian versus phreatomagmatic eruptive phases are reflected in changing groundmass crystallinity. This highlights the propensity for transitions in eruption style over seemingly short time intervals and significantly enhancing eruption explosivity.

Explosive-effusive-explosive: The role of magma ascent rates and paths in modulating caldera eruptions

Abstract One of the biggest challenges in volcanology is assessing the role of magma properties (volatile budgets, storage depths, and ascent rates) in controlling eruption explosivity. We use a new approach based on apatite to estimate volatile contents and magma ascent rates from a sequence of sub-Plinian, effusive, and Vulcanian eruption deposits at Rabaul caldera (Papua New Guinea) emplaced in 2006 CE to probe the mechanisms responsible for the sudden transitions in eruption styles. Our findings show that all magmas were originally stored at similar conditions (2–4 km depth and 1.8–2.5 wt% H2O in the melt); only the magma that formed the lava flow stalled and degassed at a shallower level (0.2–1.5 km) for several months. A more energetic batch of magma rose from depth, bypassed the transient reservoir, and ascended within ≤8 h to Earth's surface (mean velocity ≥0.2 m/s), yielding the initial sub-Plinian phase of the eruption. The shallowly degassed magma was then able to reach the surface as a lava flow, likely through the path opened by the sub-Plinian magma. The magma of the last Vulcanian phase ascended without storage at a shallow depth, albeit more slowly (ascent rate 0.03–0.1 m/s) than the sub-Plinian magma. Our study illustrates how the complexity of plumbing systems may affect eruption styles, including at other volcanic systems, and have implications for interpreting volcano monitoring data.

Stratigraphy and eruptive history of Corbetti Caldera in the Main Ethiopian Rift

The East African Rift (EAR) hosts the highest density of peralkaline volcanoes of any region globally, making it an ideal location to study the subaerial and magmatic processes of peralkaline volcanism. Corbetti Caldera is one such peralkaline centre found within the southern part of the Main Ethiopian Rift (MER), a segment of the EAR. Corbetti is actively deforming and has previously undergone large-scale Plinian eruptions. However, our broader understanding of Corbetti's evolution is limited. Here we present a detailed study of the pre-, syn-and post-caldera eruptive deposits and compile them into a composite stratigraphy of the volcanic sequence. We find evidence for multiple previously undocumented large-scale eruptions, including the deposition of two pre-caldera lithic lag breccias, and we identify three additional post-caldera obsidian lavas. We constrain the age of a young Tuff Cone, Biftu, which sits outside the caldera walls, to <7375 ± 54 cal BP through 14C dating of shells within an associated PDC deposit. The Wendo Koshe Cone, the most recent cone within the complex, is interpreted as the remains of two cones that opened in close proximity to each other and formed the vents for two pyroclastic eruptions: Bedded Pumice and Wendo Koshe Younger Pumice (WKYP). There is abundant evidence for the occurrence of pyroclastic density currents (PDC) within the caldera, usually associated with pumice cone-forming eruptions. These flow deposits rarely extend beyond the caldera walls. From our compiled stratigraphy, we estimate a recurrence rate of one eruption per 300–400 years over the last 2.3 ky.These findings are especially significant as Corbetti is earmarked for potential geothermal exploration, and an understanding of eruptive frequency and style provides vital context to assess the potential hazards associated with this future infrastructure.

Characteristics of Sub-Aerially Emplaced Pyroclasts in the Surtsey Eruption Deposits: Implications for Diverse Surtseyan Eruptive Styles

The 1963–1967 shallow-to-emergent eruption in Iceland’s Vestmannaeyjar earned a place in the history of volcanology by creating the island of Surtsey while under close observation of volcanologist Sigurdur Thorarinsson (Sigurður Þórarinsson in Icelandic). This is an example of what is now called Surtseyan volcanism, and it included explosive and effusive phases from multiple vents that formed the island of Surtsey itself, as well as one fully subaqueous pyroclastic edifice and two additional, but ephemeral, islands. Sigurdur Thorarinsson identified tephra jetting and continuous uprush as characteristic types of subaerial explosive activity of Surtseyan volcanism. Subaerial cone-forming deposits of Surtseyan volcanism are typically poorly sorted, with fine-grained beds rich in sideromelane ash fragments, punctuated by larger, ubiquitously composite bombs, whereas deposits sampled by coring deep into the submarine edifice include fines-poor horizons dominated by vesicular coarse sideromelane ash. Here, we present new textural data and highlight the diversity of pyroclasts and microtextures from Surtsey (Surtur I and Surtur II) and its satellite vents (Surtla, Syrtlingur and Jolnir), in the context of Surtseyan volcanism. We used several sample sets. Some were collected during the 3.5-year long eruption and were conserved in the Icelandic Natural History Museum, including one sample from the core drilled into Surtsey in 1979. Other samples were collected during more recent field campaigns on Surtsey Island. In closing, we discuss the implications of this diversity for the range of activity and products produced by Surtsey.

The October 14, 2021 Eruption of Nakadake First Crater, Aso Volcano (Japan): Insights from its Eruptive Deposits

The October 14, 2021 Eruption of Nakadake First Crater, Aso Volcano (Japan): Insights from its Eruptive Deposits

Rapid eruptive transitions from low to high intensity explosions and effusive activity: insights from textural analysis of a small-volume trachytic eruption, Ascension Island, South Atlantic

Proximal deposits of small-volume trachytic eruptions are an under-studied record of eruption dynamics despite being common across a range of settings. The 59 ± 4 ka Echo Canyon deposits, Ascension Island, resulted from a small-volume explosive-effusive trachytic eruption. Variations in juvenile clast texture reveal changes in ascent dynamics and transitions in eruption style. Five dominant textural types are identified within the pumice lapilli population. Early Strombolian-Vulcanian eruption phases are typified by macro- and micro-vesicular equant clast types. Sheared clasts are most abundant at the eruption peak, transitioning to dense clasts in later phases due to shear-induced coalescence, outgassing and vesicle collapse. Melt densification and outgassing via tuffisite veins increased plume density, contributing to partial column collapse and the explosive-effusive transition. Bulk vesicularity distributions indicate a shift in dominant fragmentation mechanism during the eruption, from early-stage bubble interference and rupture to late-stage transient fragmentation, with a transient peak of Plinian activity. Dome and lava groundmass crystallinities of up to 70% indicate near-complete degassing during effusive phases, followed by shallow over pressurisation and a final less explosive phase. We provide textural evidence for high-intensity explosive phases and rapid transitions in eruptive style during small-volume trachytic eruptions and consider the impact of trachytic melt compositions on underlying dynamics of these short-lived, explosive events. This analysis demonstrates the value of detailed stratigraphy in understanding critical changes in eruption dynamics and the timescales over which they may occur which is of particular value in anticipating future eruptions of this type.

Mapping and classification of volcanic deposits using multi-sensor unoccupied aerial systems

The deposits from volcanic eruptions represent the record of activity at a volcano. Identification, classification, and interpretation of these deposits are crucial to the understanding of volcanic processes and assessing hazards. However, deposits often cover large areas and can be difficult or dangerous to access, making field mapping hazardous and time-consuming. Remote sensing techniques are often used to map and identify the deposits of volcanic eruptions, though these techniques present their own trade-offs in terms of image resolution, wavelength, and observation frequency. Here, we present a new approach for mapping and classifying volcanic deposits using a multi-sensor unoccupied aerial system (UAS) and demonstrate its application on lava and tephra deposits associated with the 2018 eruption of Sierra Negra volcano (Galápagos Archipelago, Ecuador). We surveyed the study area and collected visible and thermal infrared (TIR) images. We used structure-from-motion photogrammetry to create a digital elevation model (DEM) from the visual images and calculated the solar heating rate of the surface from temperature maps based on the TIR images. We find that the solar heating rate is highest for tephra deposits and lowest for ʻaʻā lava, with pāhoehoe lava having intermediate values. This is consistent with the solar heating rate correlating to the density and particle size of the surface. The solar heating rate for the lava flow also decreases with increasing distance from the vent, consistent with an increase in density as the lava degasses. We combined the surface roughness (calculated from the DEM) and the solar heating rate of the surface to remotely classify tephra deposits and different lava morphologies. We applied both supervised and unsupervised machine learning algorithms. A supervised classification method can replicate the manual classification while the unsupervised method can identify major surface units with no ground truth information. These methods allow for remote mapping and classification at high spatial resolution (< 1 m) of a variety of volcanic deposits, with potential for application to deposits from other processes (e.g., fluvial, glacial) and deposits on other planetary bodies.

Historical volcanism in the Canary Islands; part 1: A review of precursory and eruptive activity, eruption parameter estimates, and implications for hazard assessment

Despite decadal–millennial repose periods, volcanoes of the Canary Islands pose significant, though poorly understood hazards to local communities and infrastructure. At least 13 volcanic eruptions forming monogenetic cones and lava flows have occurred in the archipelago since 1500 CE: six on the island of La Palma (in 1585, 1646, 1677–1678, 1712, 1949 and 1971), four on Tenerife (1704–1705, 1706, 1798 and 1909), two on Lanzarote (1730–1736 and 1824) and one on the submarine flank of El Hierro (2011–2012). In this paper, we synthesize available data on these historical eruptions, focusing on their physical characteristics and chronological development, and provide new estimates of eruption parameters, such as lava flow runout, area and volume, to inform volcanic hazard assessment in the archipelago. While incomplete and imprecise, historical records indicate that precursory seismicity began days to years prior to eruption onset, consistent with the three months of well-documented unrest for the 2011–2012 eruption. Excluding the atypical 1730–1736 event, eruptions lasted from ten days to a little under five months. Initial eruptive phases usually involved the opening of multiple vents along dike-fed fissures, with Strombolian explosive activity forming monogenetic cones. Lava flow emission generally quickly followed, and later eruptive phases were typically dominated by effusive behavior. Some eruptions (1704–1705, 1824 and 1949), however, had a complex evolution punctuated by the sequential opening of distinct vents several kilometers apart. Total lengths of vent-defined fissures range from 0.2 to 14.0 km, and maximum lava flow runout is 2.7–9.4 km, extending to the coastline in 75% of eruptions. Proximal eruptive deposits cover 1.8–7.8 km2. Published estimates of subaerial eruptive volumes average between 11 and 66 × 106 m3. In comparison, a new empirical relationship based on well-constrained lava flow area and volume data at other basaltic volcanoes yields volumes of 10–76 × 106 m3 for Canary Island eruptions. The 1730–1736 Timanfaya eruption on Lanzarote represents an outlier in the context of historical Canary Island volcanism, with a duration of 2055 days, a total fissure length ≥ 14.4 km defined by at least ten main emission centers, a maximum lava flow length of 21.7 km, a lava flow field area of 146 km2 and volume of at least 2.2–3.7 km3. Historical eruptive rates are low, at 1.0–2.1 × 106 m3/year or 7.3–11.0 × 106 m3/year including the 1730–1736 eruption, in agreement with long-term volcano growth rates based on geologic data. We find no evidence for time-predictable or volume-predictable behavior of the historical eruptive sequence, which has a mean recurrence interval of 39 ± 24 years. Our analysis outlines a useful framework for forecasting the onset, development and style of future eruptions in the archipelago. Further work, particularly detailed field-based studies of eruption deposits and petrologic reconstructions of eruption run-up processes, will help refine our understanding of historical volcanism and associated hazards in the Canary Islands.

Explosive felsic eruptions on ocean islands: A case study from Ascension Island (South Atlantic)

Ocean island volcanism is generally considered to be dominated by basaltic eruptions, yet felsic products associated with more hazardous explosive eruptive events are also present in the geological record of many of these islands. Ascension Island, recently recognised as an active volcanic system, exhibits explosive felsic eruption deposits but their age, eruptive styles and stratigraphic association with mafic volcanism are thus far unclear. Here we present a felsic pyroclastic stratigraphy for Ascension Island, supplemented by 26 new 40Ar/39Ar ages and whole rock geochemical XRF data. More than 80 felsic pyroclastic eruptions have occurred over the last ~ 1 Myr, including subplinian and phreatomagmatic eruptions, which produced pumice fall and pyroclastic density current deposits. Detailed sampling suggests felsic events are unevenly distributed in space and time. Subaerial activity can be divided into four Periods: Period 1 (~1000 – 500 ka) felsic and mafic eruptions, with felsic explosive eruptions, linked to a Central Felsic Complex; Period 2 (~ 500 – 100 ka) mafic period; Period 3 (~ 100 – 50 ka) felsic eruptions associated with the Eastern Felsic Complex; Period 4 (< 50 ka) mafic eruptions. The last explosive eruption occurred at ~ 60 ka. This work highlights the cyclical nature of ocean island volcanism and the timescales over which changes between predominantly mafic and felsic volcanism occur. The prevalence of past felsic explosive eruptions on Ascension highlights the need to consider the possibility of future subplinian or phreatomagmatic events in hazard management plans, with any potential risk compounded by Ascension’s small size and remote location.

Magmatic Processes at La Soufrière de Guadeloupe: Insights From Crystal Studies and Diffusion Timescales for Eruption Onset

Signals of volcanic unrest do not usually provide insights into the timing, size and style of future eruptions, but detailed analysis of past eruptions may uncover patterns that can be used to understand future eruptive behavior. Here, we examine basaltic-andesitic to andesitic eruption deposits from La Soufrière de Guadeloupe, covering a range of eruption styles, ages and magnitudes. Our work is timely given unrest at La Soufrière de Guadeloupe has increased over the last 25 years. We constrain the timescales of magmatic processes preceding four eruptions: 1657 Cal. CE (Vulcanian), 1010 Cal. CE (Plinian), ∼341 Cal. CE (Strombolian) and 5680 Cal. BCE (La Soufrière de Guadeloupe’s first known Plinian eruption). Using crystal-specific analyses of diffusion in orthopyroxenes, we calculate the timescale occurring between the last recharge/mixing event in the magma reservoir and the eruption. We use backscattered electron images, coupled with EMPA of the outermost crystal rim, to derive magmatic timescales. We model the timescale populations as random processes whose probability distributions provide expected (“mean”) timescales and the associated standard errors for each eruption. This provides a new statistical method for comparing magmatic timescales between disparate eruptions. From this, we obtain timescales of magma storage at La Soufriére de Guadeloupe ranging from 18.8 ± 0.37 days to 361 ± 0.40 days, with no clear distinction between eruption style/size and timescales observed. Based on these data, magmatic interaction timescales are a poor predictor of eruption style/size. This study shows that magmatic processes prior to eruption can occur on relatively short timescales at La Soufrière de Guadeloupe. Further to this basaltic-andesitic to andesitic volcanoes can rapidly produce large-scale eruptions on short timescales. These relatively short timescales calculated for volcanic processes at this system constitute a critical new data set and warrant an urgency in enhancing modeling and interpretation capabilities for near-real time monitoring data. These integrated efforts will improve early warning, eruption forecasting and crisis response management for different scenarios, as well as planning for long-term risk reduction.

The magmatic and eruptive evolution of the 1883 caldera-forming eruption of Krakatau: Integrating field- to crystal-scale observations

Explosive, caldera-forming eruptions are exceptional and hazardous volcanic phenomena. The 1883 eruption of Krakatau is the largest such event for which there are detailed contemporary written accounts, allowing information on the eruptive progression to be integrated with the stratigraphy and geochemistry of its products. Freshly exposed sequences of the 1883 eruptive deposits of Krakatau, stripped of vegetation by a tsunami generated by the flank collapse of Anak Krakatau in 2018, shed new light on the eruptive sequence. Matrix glass from the base of the stratigraphy is chemically distinct and more evolved than the overlying sequence indicating the presence of a shallow, silicic, melt-rich region that was evacuated during the early eruptive activity from May 1883 onwards. Disruption of the shallow, silicic magma may have led to the coalescence and mixing of chemically similar melts representative of a range of magmatic conditions, as evidenced by complex and varied plagioclase phenocryst zoning profiles. This mixing, over a period of two to three months, culminated in the onset of the climactic phase of the eruption on 26th August 1883. Pyroclastic density currents (PDCs) emplaced during this phase of the eruption show a change in transport direction from north east to south west, coinciding with the deposition of a lithic lag breccia unit. This may be attributed to partial collapse of an elevated portion of the island, resulting in the removal of a topographic barrier. Edifice destruction potentially further reduced the overburden on the underlying magmatic system, leading to the most explosive and energetic phase of the eruption in the morning of 27th August 1883. This phase of the eruption culminated in a final period of caldera collapse, which is recorded in the stratigraphy as a second lithic lag breccia. The massive PDC deposits emplaced during this final phase contain glassy blocks up to 8 m in size, observed for the first time in 2019, which are chemically similar to the pyroclastic sequence. These blocks are interpreted as representing stagnant, shallow portions of the magma reservoir disrupted during the final stages of caldera formation. This study provides new evidence for the role that precursory eruptions and amalgamation of shallow crustal magma bodies potentially play in the months leading up to caldera-forming eruptions.

Basaltic phreatomagmatic fissure at 71 Gulch Part 1: sediment magma mingling and eruptive behavior

71 Gulch Volcano, located in the western Snake River Plain, southwestern Idaho (USA), was formed by a basaltic fissure eruption into Pliocene Lake Idaho. Deposits at and below the eruptive surface record the nature of explosive and non-explosive sediment-magma and water-magma interactions. The paleoenvironment and the volcanic plumbing system of 71 Gulch eruption were reconstructed from a detailed study of the now-exposed eruptive and subsurface deposits. Estimated water levels during the eruption range from 1 to 53 m across the entire volcano based on the distribution of pillow lavas. Billowed dikes and fluidal peperites are two types of intrusive features found ≤ 12 m below the syn-eruptive surface that have similar continuous margins representing ductile behavior and emplacement into soft, deformable sediment. In comparison, tabular dikes and blocky peperites occur throughout 41 m thick of exposed deposits below the syn-eruptive surface. A conical, diatreme-like vent structure dominates the subsurface exposure, indicating excavation by phreatomagmatic explosions. Localized spatter within the main subsurface vent suggests temporary exclusion of water and thus a period of brief vent growth above the lake level. Evidence of sediment-magma mingling through blocky and fluidal peperites shows how differing subsurface depths impact the resulting mingling textures.

Evidence for a large-magnitude Holocene eruption of Mount Rittmann (Antarctica): A volcanological reconstruction using the marine tephra record

In Antarctica, the near-source exposures of volcanic eruption deposits are often limited as they are not well preserved in the dynamic glacial environment, thus making volcanological reconstructions of explosive eruptions extremely challenging. Fortunately, pyroclastic deposits from explosive eruptions are preserved in Southern Ocean sediments surrounding Antarctica, and the tephrostratigraphy of these sequences offers crucial volcanological information including the timing and tempo of past eruptions, their magnitude, and eruption dynamics. Here we report the results of a tephrostratigraphy and tephrochronology study focused on four sediment cores recovered from the Wood Bay area in the western Ross Sea, Antarctica. In all these sedimentary sequences, we found a well-stratified primary tephra of considerable thickness, up to 80 cm, hereafter named the Aviator Tephra (AVT). According to the characteristics of the tephra deposit and its distribution, the AVT was associated with an eruption of considerable intensity, potentially representing one of the largest Holocene eruptions recorded in Antarctica. Based on the major and trace element geochemistry and the mineral assemblage of the tephra, Mount Rittmann was identified as the source of the AVT. A Holocene age of ∼11 ka was determined by radiocarbon dating organic material within the sediments and 40Ar-39Ar dating of alkali-feldspar crystals included in the tephra. Eruption dynamics were initially dominated by hydromagmatic magma fragmentation conditions producing a sustained, relatively wet and ash-rich eruptive cloud. The eruption then evolved into a highly energetic, relatively dry magmatic Plinian eruption. The last phase was characterized by renewed efficient magma-water interaction and/or collapse of the eruptive column producing pyroclastic density currents and associated co-ignimbritic plumes. The distal tephra deposits might be linked to the widespread lag breccia layer previously identified on the rim of the Mount Rittmann caldera which share the same geochemical composition. Diatoms found in the sediments surrounding the AVT and the primary characteristics of the tephra indicate that the Wood Bay area was open sea at the time of the eruption, which is much earlier than previously thought. AVT is also an excellent tephrostratigraphic marker for the Wood Bay area, in the Ross Sea, and a useful marker for future synchronization of continental ice and marine archives in the region.

Solubility, diffusivity, and O isotope systematics of H2O in rhyolitic glass in hydrothermal temperature experiments

In many volcanic settings, eruptive deposits experience prolonged cooling in the presence of water, such as in subglacial or submarine eruptions. Under these conditions, volcanic glass will rehydrate and record the isotopic composition of the water. This isotope exchange is moderated by H2O solubility and diffusivity in the glass. In this study, we report results from glass hydration experiments conducted at 175–375 °C to constrain H2O solubility and diffusivity under these hydrothermal conditions over timescales lasting hours to months. We use anhydrous high and low silica rhyolites as well as hydrous high silica rhyolite (perlites) with isotopically labeled water as starting materials. Measurements of bulk H2O by TC/EA of experimental glasses provide minimum H2O solubility estimates. High-Si rhyolitic glass has an H2O solubility between 2.75 wt.% (175 °C, 0.89 MPa) and 4.1 wt.% (375 °C, 21 MPa) while low-Si rhyolite H2O solubility is uniformly ∼0.5 wt.% higher at each temperature. We find a roughly linear relationship of solubility vs 1/T that is ∼1–2 wt.% greater than extrapolations from magmatic temperature solubility relationships. Furthermore, three independent methods of diffusion modeling – one in situ and two mass balance approaches – all produce H2O diffusivity (DH2O) values that up to 5.5 times greater than predicted by extrapolation of the 1/T – DH2O relationships above 400 °C to the experimental P-T-XH2O conditions. In situ H2O profiles in rhyolite particles measured by NanoSIMS have the characteristic “snowplow ” functional form that arises from the H2O concentration dependence of DH2O. We cannot detect diffusively driven kinetic fractionation of D relative to H with the NanoSIMS data. Diffusion and mass balance calculations that fit TC/EA time series of bulk H2O in particles of a single size distribution, and calculations that reconcile two sets of different sized particles at a single experimental duration, return similar DH2O constraints. We also present time series δ18O of bulk glass (δ18Obulk) and the δ18O of water-in-glass (δ18Owig) measurements, which indicate that molecular water (H2Om) dissolved in the glass is the primary driver of subsequent oxygen isotope exchange between glass and an external fluid. Local equilibrium between the δ18Owig and the δ18Obulk is rapidly established and ranges from approximately −14‰ at 175 °C to −10‰ at 375 °C. Both the δ18Obulk and δ18Owig then increase with time moving slowly towards estimated bulk glass δ18O equilibrium with the external experimental water. Oxygen isotope exchange between glass and a fluid is therefore strongly linked to – and is limited by – H2O diffusivity, which is slower at lower P-T conditions and lower H2O solubilities as H2Om diffusion is the main exchange mechanism.

Volcanogenic mass flow deposits and seafloor diapirism following the largest insular Quaternary eruption of the eastern Mediterranean at Nisyros island, Aegean volcanic arc

Nisyros volcanic island, at the eastern end of the Aegean Volcanic Arc, was mainly constructed after the ultra-Plinian Kos Plateau Tuff (KPT) eruption at 161 ka. The surrounding submarine area consists mostly of marginal mass-transport deposits that commonly characterize insular stratovolcanoes. This study aims at providing insights into the deposition and volume of such deposits by elucidating the products of a mega-eruption and subsequent paroxysmal volcanicity, typical of subduction zone-island arc systems. Seismic reflection and multibeam bathymetry around Nisyros identify pyroclastic and debris flow deposits covering areas several orders of magnitude greater than the island. The entire seabed between the basins of East Kos and Tilos is underlain by a ~7 km3 volcaniclastic unit that defines a ubiquitous basal unconformity at an average depth of 30 m below the seafloor. Southwest of Nisyros, two groups of avalanche deposits from the same unit are bathymetrically identified on the slopes of the northernmost Karpathos basin apron. Seismic stratigraphic markers that trace the unit on the shelf of Tilos suggest it is concomitant with the KPT eruption. This formerly unknown submarine expansion of the KPT deposits into three neighboring basins, when added to the volume of this massive unit to the rest of the Nisyros surroundings, gives it an explosivity index (VEI) >6. As such, it represents the largest Quaternary subaqueous volcanogenic mass flow deposit of the eastern Mediterranean. From this dataset, it can be inferred that the submarine advance of the erupted material occurred mainly through erosive gravity flows, envisioned as the main dispersion mechanism of large-scale subaqueous pyroclastic deposits of Plinian eruptions. East of Nisyros, unique small-scale diapiric domes and seafloor mounds are attributed to loading by the KPT in combination with regional faulting. Subsequent Nisyros effusive activity produced pyroclastic units around the northeast as well as debris avalanche and lava flows south of the island. These have been correlated to known onshore formations. The present study documents the intensity and impacts of a volcanic island mega-eruption and paroxysmal epilogue over a cycle of 100 kyr.

Potentiality of the Use of Pyroclastic Volcanic Residues in the Production of Alkali Activated Material

Volcanic rocks have been used for building activity by the inhabitants of important cities located on the slopes of Mt. Etna, Italy. In this paper, the potential use of volcanic residues (code 20 03 03—“Municipal waste” residues from road cleaning in the European Waste Catalogue (EWC)) for the production of alkali activated material, especially devoted to the restoration of buildings belonging to the Baroque Sicilian architecture, was investigated. In particular, large volcanic pyroclastic deposits of recent eruptions considered waste materials were studied and a volcanic paleo-soil, locally named ghiara, widely used for mortars and plaster production in XVII–XVIII century with good pozzolanic features, was also considered. Both volcanic materials were activated using different mixtures of NaOH and Na2SiO3. Furthermore, formulations with different amount of metakaolin addition (10–25 wt%) were prepared due to low reactivity of volcanic materials and to allow the activation at room temperature. X ray diffraction revealed the formation of small quantities of zeolites as a result of the alkali activation process. The mechanical-physical results evidenced that the mechanical strength is strongly dependent on the metakaolin amount (10–38 MPa); accessible porosity average 25% and an average pore diameter of 0.06 µm; water absorption range 9–15%, eluates conductivity in the range 20–350 µS/m. These results confirm the occurring of alkali activation and the good potential for these pyroclastic wastes for valorization in the restoration field.Graphic