Past Eruptions Research Articles

An ultra-high-resolution autonomous uncrewed helicopter aeromagnetic survey in Izu-Oshima Island, Japan

We conducted a high-resolution aeromagnetic survey using an autonomously driven uncrewed helicopter that flew as low as several tens of meters above the ground along precise flight tracks with 1 m accuracy. The geomagnetic total intensity was measured by a total intensity magnetometer suspended beneath the helicopter at a ~ 50 m or less flight spacing over the entire caldera of Mt. Mihara, located on Izu-Oshima Island, Japan. From the observed geomagnetic data, we estimated high-resolution subsurface magnetization intensity. A high average magnetization intensity of 13.5 A/m was obtained for the entire caldera. The distribution of the magnetization intensity was not only consistent with the results of conventional airborne surveys, but it also had a high spatial resolution of less than 100 m. Highly magnetized areas were observed along the NW–SE lines that intersected the summit pit crater, Crater A, which is consistent with the principal stress direction of Izu-Oshima Island. These highly magnetized areas might be solidified magma that did not reach the surface during past eruptions. A large and deep-rooted weakly magnetized area was found just outside of the NE side of the central cone, which corresponds to the location of Fissure B, and the conduit must have been demagnetized at the previous event. Other weakly magnetized areas were also observed at the N, E, and SW sides around the pit crater. These regions correspond to the location of fumaroles in the crater. The high-resolution subsurface magnetization imaged by the autonomous uncrewed helicopter will be helpful for the mitigation of future eruption damage by enabling the assessment of potential fissure eruption areas.

Bottom-up vs top-down drivers of eruption style: Petro-geochemical constraints from the holocene explosive activity at La Soufrière de Guadeloupe

Signals of volcanic unrest have been used successfully to provide insights into the timing, magnitude, intensity, and style of future eruptions. However, in order to provide context for the subsequent activity, analysis of past eruptions is required. This provides useful information in order to understand processes of magma genesis, storage, evolution and ascent which lead to the onset of eruptions. Here, we examine basaltic-andesitic to andesitic deposits from La Soufrière de Guadeloupe Holocene eruptions, covering a range of explosive eruption styles, ages and magnitudes. Our work is timely given unrest at this system has increased over the last 25 years, with a potential eruption capable of directly impacting up to 80,000 people in Southern Basse-Terre and potentially thousands more indirectly on a regional scale. We report on the geochemistry of pre-eruptive magmas using detailed analyses of glass (melt inclusions and groundmass glass) from four Holocene explosive eruptions: 1657 Cal. CE (Vulcanian, VEI 2), 1530 Cal. CE (sub-Plinian, VEI 3), 1010 Cal. CE (Plinian, VEI 4), and 5680 Cal. BCE (Plinian, VEI 4). Major element concentrations vs SiO2 in whole rock (WR), groundmass glass (GM) and melt inclusions (MI) show a strong linear trend. MIs reveal a relatively homogenous melt composition from the first to the most recent eruptions, ranging from 63.6–78.7 wt% SiO2. Volatiles, including H2O (2.3–4.4 wt%), CO2 (35–866 ppm) and sulphur (30–202 ppm), are also consistent across the various eruptions. The major element and volatile compositional homogeneity across the eruptions indicates that composition and volatiles do not have a direct control on eruption explosivity at this system. Instead, we find differences in ascent rate, groundmass glass viscosity and microlite volume percentage, indicating that explosive eruptive style at La Soufrière is controlled by a combination of ascent rate and top-down controls affecting rock strength, stress distribution and the development of fluid overpressure. Rapid ascent in the absence of top-down controls (processes with a cause external to the magma but affecting the plumbing system) will result in explosive eruptions driven from the bottom-up (internal to magma dynamic response with varying pressure and temperature, e.g., 1010 Cal. CE in the case of very rapid ascent or 1657 Cal. CE in the case of rapid ascent). However, we also highlight the importance of top-down controls, such as conduit sealing which can promote the onset of explosive eruptions, even in the case of slow magma ascent (e.g., 5680 Cal. BCE). External effects (including ingress of water and rapid edifice unloading) can also favour explosive eruptions with flank collapses involved in some scenarios (e.g., 1530 Cal. CE). The multiple controls on explosive eruption style make this system more hazardous and complex to model and monitor. In order to improve early-warning system efficiency, forecast models, eruption scenario crisis response and long-term risk reduction planning, we stress that internal processes such as fracture and host-rock sealing (fluid pore pressure) as well as external processes such as water moving into the system and the mechanical stability of the edifice should be monitored and modelled closely.

A 22,000-year tephrostratigraphy record of unidentified volcanic eruptions from Ternate and Tidore islands (North Maluku, Indonesia)

Investigating past eruptions gives a unique opportunity to understand volcanic hazards, particularly in Indonesia, where volcanic eruptions occur frequently. Here, we present the first reconstruction of the eruptive history of the Ternate and Tidore Islands (North Maluku, Indonesia) over the past 22,000 years cal. BP, based on a new identification and characterization of past volcanic events methodological approach. This multidisciplinary study (geomorphology, tephrochronology, sedimentology, geochronology, geochemistry) constitutes the first stratigraphic and chronological continuum from volcanic deposits found in a set of fifteen sections established in Ternate, Tidore, and Maitara Islands. Sedimentological and geochemical data from tephrostratigraphy studies and radiocarbon dating suggest that these islands experienced at least four major explosive events from c. 22,000 to 740 years cal. BP. The oldest event recorded is a Plinian eruption associated with a caldera-forming eruption of Telaga volcano on Tidore Island at c. 22,000–17,500 cal. BP. A second pumiceous eruption dated at c. 18,000 cal. BP is attributed to the last Plinian eruption of Gamalama volcano on Ternate, whose current eruptive activity is mainly strombolian or phreatomagmatic. A succession of pyroclastic deposits of phreatomagmatic origin is related to the Ngade maar formation on Ternate Island, and the abundant deposits of scoria, pumice, and ash found in all sites probably occurred c. 14,500–13,000 cal. BP. No eruptions of the Kie Matubu volcano on Tidore Island have been reported by human beings since their presence in the region from the 16th century, but this study highlights two late Holocene eruptions, c. 2500 cal. BP and 740 cal. BP. This first chronostratigraphic framework from the late Pleistocene to recent eruptions in this region, sheds new light concerning the management of prediction and warning information about potential eruptions that may occur on these small volcanic islands in the future.

Supergreen Trees Can Signal Sites of Eruptions

Tree core chemistry can explain what happened before Mount Etna’s 2002 eruption and suggests that trees could play a role in rebuilding past eruptions.

Moving for safety: a qualitative analysis of affected communities\u2019 evacuation response during the 2014 Mayon Volcano eruption

This study looks at the 2014 Mayon Volcano eruption to identify possible factors that contribute to the actions that people (local authorities/officials, community leaders, and residents) take during an eruptive period. We used qualitative analysis to examine interviews of people who experienced the August–December 2014 Mayon Volcano unrest, to determine the nature of people’s understanding of hazards and risks, their decision-making, and response process. The thematic analysis shows that residents reacted to the information given to them in several ways- they evacuated when ordered (mandatory), chose not to evacuate for various reasons (e.g. they did not believe they are in danger citing experiences, inconvenience in evacuation sites, etc.), and evacuated even when not ordered to (voluntary). The local officials and community leaders were asked about their views on the possible reasons or motivations as to why residents would evacuate, and common themes that emerged were fear emanating from the experience of past eruptions, obeying the order to evacuate because it is the law, and order from provincial authorities (setting aside personal opinion on the state of the volcano based on experiential knowledge), and the potential to receive relief goods for those who are economically in need. This paper also looks at the challenges to local officials when an eruptive episode occurs- but the event falls short of the expected typical explosive behavior from the volcano. This study argues for people’s experiential knowledge as an important factor in shaping views about hazards and risks that leads to the decision-making of individuals and its importance in risk communication strategies.

Volcanological evolution of Montagne Pelée (Martinique): A textbook case of alternating Plinian and dome-forming eruptions

Montagne Pelée is one of the most active volcanoes of the Lesser Antilles arc, with two to three magmatic eruptions per millennium and an estimated magmatic production rate in the order of 0.7 km3/1000 years. Montagne Pelée is also infamous for the very large number of people (30000) killed by an eruptive phenomenon at the onset of the 1902–1905 dome-forming eruption. Active for ~550 kyrs, Montagne Pelée has undergone two major flank collapses that influenced its volcanological as well as magmatic evolution. The last one occurred at around 36 ka. Due to changes in the threshold effect following the decrease in load of the volcanic edifice due to flank collapse, there was a switch in emitted magma from generally andesitic to basaltic andesites. After 10 kyrs of intense activity, the load exerted by the new edifice once again prevented dense basaltic andesite magma from reaching the surface, whereas andesitic magmas, similar to the initial ones, continued to be emitted. All the magmas come from a common magma ponding zone at 200 ± 50 MPa, 875 ± 25 °C, an oxygen fugacity (fO2) between 0.4 and 0.8 log unit above the nickel‑nickel oxide (NNO) oxygen buffer, and melt H2O contents of 5.3–6.3 wt%. Based on comparative on-land and marine tephrochronological studies, we have reconstructed a detailed eruptive history of the volcano over the last 25 kyrs. The volcano produced a succession of Plinian-SubPlinian and dome-forming eruptions, making it a textbook case for studying this duality, which sometimes occurred during a single eruption. We identified more than 55 magmatic eruptions, with a ratio of 2/3 for dome-forming vs. Plinian eruptions. An unusual feature of this volcano is that dome-forming eruptions often start with violent, superficial and laterally directed explosions. These generate highly devastating dilute and turbulent pyroclastic density currents on the southwestern and southern flanks of the volcano, as illustrated by the seven events of this type during the first months of the 1902–1905 eruption. On the basis of the past eruptions over the last millennia, a series of scenarios can be proposed in the event of reactivation, including no magmatic eruption, a phreatic event or a magmatic eruption (Plinian or dome-forming eruption, with or without an explosive phase).

Chemical Signals in Tree Rings from Northern Patagonia as Indicators of Calbuco Volcano Eruptions since the 16th Century

The Calbuco volcano ranks third in the specific risk classification of volcanoes in Chile and has a detailed eruption record since 1853. During 2015, Calbuco had a sub-Plinian eruption with negative impacts in Chile and Argentina, highlighting the need to determine the long-term history of its activity at a high-resolution time scale to obtain a better understanding of its eruptive frequency. We developed a continuous eruptive record of Calbuco for the 1514–2016 period by dendrochemical analysis of Fitzroya cupressoides tree rings at a biennium resolution using inductively coupled plasma–mass spectrometry. After comparing the chemical record of 20 elements contained in tree rings with historical eruptions, one group exhibited positive anomalies during (Pb/Sn) and immediately after (Mo/P/Zn/Cu) eruptions, with a Volcanic Explosivity Index (VEI) ≥ 3, and so were classified as chemical tracers of past eruptions (TPE). The tree-ring width chronology also exhibited significant decreases in tree growth associated with eruptions of VEI ≥ 3. According to these records, we identified 11 new eruptive events of Calbuco, extending its eruptive chronology back to the 16th century and determining a mean eruptive frequency of ~23 years. Our results show the potential to use dendrochemical analysis to infer past volcanic eruptions in Northern Patagonia. This information provides a long-term perspective for assessing eruptive history in Northern Patagonia, with implications for territorial planning.

The Life of Volcanic Rocks During and After an Eruption

Volcanoes are constantly growing and changing. Every time a volcanic eruption occurs, new rock is added to the surrounding area. These eruptions play a big part in the formation and destruction of rocks as well as in shaping the Earth’s surface. Yet, we do not know everything about the histories of the volcanoes that previously existed on Earth. Volcanologists—scientists that study volcanoes—can study the types of rocks that volcanoes produce, to gain a better understanding of volcanoes. These rocks vary based on the characteristics of the volcano from which they came. Volcanic rocks are unique because we can study them to accurately discover when and how they were formed. In this article, we explain the processes that make volcanic rocks and formations look different from each other. We also discuss ways that volcanologists can determine how ancient volcanoes were made, by studying the rocks produced during past eruptions.

Reconstructing eruptions at a data limited volcano: A case study at Gede (West Java)

Understanding past eruption dynamics at a volcano is crucial for forecasting the range of possible future eruptions and their associated hazards and risk. In this work we use numerical models to recreate the footprints of pyroclastic density currents (PDCs) and tephra fall from three eruptions at Gede volcano, Indonesia, with the aim of gaining further insight into these past eruptions and identifying suitable eruption source parameters for future hazard and risk assessment. Gede has the largest number of people living within 100 km of any volcano worldwide, and has exhibited recent unrest activity, yet little is known about its eruptive history. For PDCs, we used Titan2D to recreate geological deposits dated at 1.2 and c. 1 kyrs BP. An objective and quantitative multi-criteria method was developed to evaluate the fit of 342 model simulations with field observations. In recreating the field deposits we were able to identify the best fitting values to reconstruct these eruptions. We found that the 1.2 kyrs BP geological deposits could be reproduced with Titan2D using either a dome-collapse or a column-collapse as the triggering mechanism, although a relatively low basal friction angle of 6° would suggest that the PDCs were highly mobile. For the 1 kyrs BP PDC, a column-collapse mechanism and a higher basal friction angle were required to fit the geological deposits. In agreement with previous studies, we found that Titan2D simulations were most sensitive to the basal friction angle parameter. We used Tephra2 to recreate historic observations of tephra dispersed to Jakarta and Gunung Patuha during the last known magmatic eruption of Gede in 1948. In the absence of observable field deposits, or detailed information from the published literature, we stochastically sampled eruption source parameters from wide ranges informed by analogous volcanic systems, allowing us to constrain the eruption dynamics capable of dispersing tephra to the most populous city in Indonesia, Jakarta. Our modelling suggests that the deposition of tephra fall in Jakarta during the November 1948 eruption was a very low probability event, with a < 1% chance of occurrence. Through this work, we show how the reconstruction of past eruptions with numerical models can improve our understanding of past eruption dynamics, when faced with epistemic uncertainty. At Gede volcano, this provides a crucial step towards the reduction of risk to nearby populations through volcanic hazard assessment.

Paleomagnetic dating of prehistoric lava flows from the urban district of Catania (Etna volcano, Italy)

Abstract Determining the ages of past eruptions of active volcanoes whose slopes were historically inhabited is vitally important for investigating the relationships between eruptive phenomena and human settlements. During its almost three-millennia-long history, Catania—the biggest city lying at the toe of Etna volcano—was directly impacted only once by the huge lava flow emplaced during the A.D. 1669 Etna flank eruption. However, other lava flows reached the present-day Catania urban district in prehistoric ages before the founding of the city in Greek times (729/728 B.C., i.e., 2679/2678 yr B.P.). In this work, the Holocene lava flows of Barriera del Bosco, Larmisi, and San Giovanni Galermo, which are exposed in the Catania urban district, were paleomagnetically investigated at 12 sites (120 oriented cores). Paleomagnetic dating was obtained by comparing flow-mean paleomagnetic directions to updated geomagnetic reference models for the Holocene. The Barriera del Bosco flow turns out to represent the oldest eruptive event and is paleomagnetically dated to the 11,234–10,941 yr B.P. and 8395–8236 yr B.P. age intervals. The mean paleomagnetic directions from the San Giovanni Galermo and Larmisi flows overlap when statistical uncertainties are considered. This datum, along with geologic, geochemical, and petrologic evidence, implies that the two lava flows can be considered as parts of a single lava field that erupted in a narrow time window between 5494 yr B.P. and 5387 yr B.P. The emplacement of such a huge lava flow field may have buried several Neolithic settlements, which would thus explain the scarce occurrence of archaeological sites of that age found below the town of Catania.

Dating Lake Sediments Using Compound‐Specific 14C Analysis of C16 Fatty Acid: A Case Study From the Mount Fuji Volcanic Region, Japan

AbstractLake sediments in volcanic regions contain continuous records of past eruptions and their environmental consequences. However, the frequent scarcity of plant material in lake sediments makes it difficult to provide robust age estimates. In this study, we performed compound‐specific radiocarbon analysis (CSRA) of fatty acids in a sediment core from Lake Kawaguchi in the Mount Fuji volcanic region, Japan, to assess their potential for dating sediments. The C16 fatty acid in the core top sediments exhibits an almost identical age (983 ± 56 years BP) to that of dissolved inorganic carbon in the modern lake surface water, which confirms that the carbon of this compound is derived from lake phytoplankton. Comparison of the 14C age between the C16 fatty acid and a plant leaf at the widespread (Amagi‐Kawagodaira) tephra layer revealed a lake reservoir age of 1,003 ± 73 14C years at ca. 3,150 cal BP, which is consistent with the modern lake reservoir age and the 14C age of the C16 fatty acid in the core top sediments, within error. The reservoir‐corrected 14C age of the C16 fatty acid yielded a modeled age of 2,837 ± 78 cal BP for the Mount Fuji Tephra (Omuro scoria‐fall deposit) in the core. This age is in good agreement with the age determined from plant remains in the same core (2,938 ± 29 cal BP), indicating that CSRA of C16 fatty acid has the potential to date lake sediments after reservoir age correction, even in sediments with limited occurrence of plant macrofossils.

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.

Global hydroclimatic response to tropical volcanic eruptions over the last millennium

Large tropical volcanic eruptions can affect the climate of many regions on Earth, yet it is uncertain how the largest eruptions over the past millennium may have altered Earth's hydroclimate. Here, we analyze the global hydroclimatic response to all the tropical volcanic eruptions over the past millennium that were larger than the Mount Pinatubo eruption of 1991. Using the Paleo Hydrodynamics Data Assimilation product (PHYDA), we find that these large volcanic eruptions tended to produce dry conditions over tropical Africa, Central Asia and the Middle East and wet conditions over much of Oceania and the South American monsoon region. These anomalies are statistically significant, and they persisted for more than a decade in some regions. The persistence of the anomalies is associated with southward shifts in the Intertropical Convergence Zone and sea surface temperature changes in the Pacific and Atlantic oceans. We compare the PHYDA results with the stand-alone model response of the Community Earth System Model (CESM)-Last Millennium Ensemble. We find that the proxy-constrained PHYDA estimates are larger and more persistent than the responses simulated by CESM. Understanding which of these estimates is more realistic is critical for accurately characterizing the hydroclimate risks of future volcanic eruptions.

The 2004–2005 Mt. Etna Compound Lava Flow Field: A Retrospective Analysis by Combining Remote and Field Methods

AbstractMapping lava flows frequently during effusive eruptions provides crucial parameters to better understand their dynamics, in turn improving our ability to model lava flow behavior. New photogrammetric methods have recently been developed, shifting the paradigm of photogrammetry from pure method to a multidisciplinary approach able to reduce the cost of volcanic monitoring and widen the potential spectrum of application. In this work, we demonstrate how multi‐view and single‐view photogrammetry methods can be used effectively to extract accurate quantitative information from photographs taken during routine surveys over an active lava flow. One intriguing advantage of these methods is that they can re‐use images acquired previously to extract new data from past eruptions. In particular, we reconstructed quantitatively the evolution of the lava flow field emplaced during 2004–2005 at Mt. Etna, subdivided in five eruptive phases from the earliest simple lava flows to the final compound lava field about 6 months later. Our results show that, in the first week of eruption, lava field formation was characterized by an increasing lava length that followed a power law growth and by a decreasing front velocity that followed a power law as well. Thereafter, the length increasing became almost constant until the developed lava tube system was able to drain the lava for long distances, with the area inundated by lava that grew linearly in the first 20 days. Finally, we demonstrate the crucial role that the syn‐eruptive DEMs acquisition could have to improve our understanding of the emplacement dynamics of complex lava fields.

Rancho Seco monogenetic volcano (Michoacán, Mexico): Petrogenesis and lava flow emplacement based on LiDAR images

Given the high eruption recurrence in the Michoacán-Guanajuato volcanic field (MGVF) in central Mexico, the birth of a new monogenetic volcano can be expected in the future. It is important, therefore, to reconstruct the past eruptions of its many different volcanoes, including estimates of lava flow emplacement times and their rheological properties. These studies define the range of possible future eruptive scenarios and are necessary to evaluate potential risk. The Rancho Seco monogenetic volcano, located in the central part of the MGVF (19°37′03”N, 101°28′21”W), was radiocarbon-dated at ~27,845 years BP. Its eruption initiated with a violent-Strombolian phase that produced a scoria cone and was followed by the effusion of at least seven associated andesitic lava flows, reflecting drastic changes in the eruptive dynamics. Effusive activity probably involved decreases in the magma ascent and discharge rates linked to efficient degassing in an open system. Lava chemical composition suggest an origin of partial melting of a subduction-modified hydrated heterogenous mantle wedge and textural and mineralogical analysis indicates significant crystal fractionation and minor assimilation of granodioritic basement rocks. High-resolution LiDAR imagery was used to estimate lava flow viscosities and emplacement times by following a morphology-based methodology. Results indicate that lava flow viscosities ranged from 105 to 109 Pa·s and emplacement durations between 32 and 465 days for the flow units considered (F5 and F6). The entire eruption may have lasted from 2 to 6 years with a mean effusion rate of 4 to 15 m3/s. Our results are also pertinent to archaeologists studying the architectural remains of Angamuco, a large urban pre-Hispanic site built on Rancho Seco's lava flows.

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.

The Impact of Eruption Source Parameter Uncertainties on Ash Dispersion Forecasts During Explosive Volcanic Eruptions

AbstractVolcanic ash in the atmosphere is a hazard to aviation. To predict which areas of airspace are most likely to be affected by the presence of ash, Volcanic Ash Advisory Centers (VAACs) use observations and atmospheric dispersion models. These models are initialized with, among other parameters, a mass eruption rate (MER), which quantifies the emission rate into the atmosphere at the source. This influences the predicted spatial–temporal evolution and concentration of the ash cloud. Different models are available to estimate MER from the volcanic plume height and some models also include the weather conditions (e.g., wind speed). The REFIR software tool uses time‐series of plume height estimated from observations and weather data to provide estimates of MER through time. Here we present an updated version of REFIR that can now be used also to calculate MER for past eruptions and produce output parameters in a format suitable for use with the NAME dispersion model (UK Met Office—London VAAC). We also investigate how uncertainty in input parameters is propagated through to dispersion model output. Our results show that a +/−1 km uncertainty on a 6 km high plume can result in the affected area ranging by a factor of three between the minimum and maximum estimates. Additionally, we show that using wind‐affected plume models results in affected areas that are five times larger than using no‐wind‐affected models. This demonstrates the sensitivity of MER to the type of plume model chosen (no‐wind‐ vs. wind‐affected).

Reconstructing eruptions from historical accounts: Makaturing c. 1765, Philippines

For some volcanoes, the only evidence for past eruption is provided by historical accounts. When interpreted carefully, these have the potential to be a rich source of information, and yet they have so far been under-utilised in reconstructing eruption histories. The navigator Thomas Forrest describes a large eruption at Makaturing volcano, southern Philippines, in approximately 1765 that he considers the catalyst for the local Iranun population transitioning from an agrarian society to long-distance piracy and slave raiding. Within the historical literature, the eruption is attributed to large scale physical impacts around the volcano and disruptions to trading routes and livelihoods that ultimately changed the course of southeast Asia's history. However, no such eruption (or impacts) are recognised in the scientific literature or in eruption databases, and fieldwork to the region remains difficult. Here, we reinterpret the account of Forrest from a multi-disciplinary perspective, with a historian and physical volcanologists working together to incorporate the greatly needed local context into identifying credible volcanic processes and impacts associated with the reported activity. We used a novel approach to eruption reconstruction by cross-referencing deposits and impacts inferred from the historical record with stochastic tephra dispersal modelling that considered multiple eruption sources and characteristics. We found that Forrest's account was best characterised by an eruption of ~VEI 4 between May and October, with plume heights in the range of 12 to 16 km. While at least one eruption of this size was required to reproduce the impacts described in the historical record, it may have formed part of a longer sequence of multiple, repeated eruptions. In this way, such an eruption could have acted as a ‘tipping point’ for a local population already on the verge of socio-political and economic collapse, disproportionately affecting regions on a much larger scale than the reported deposits suggest. There remains a disconnect between the eruption characteristics recorded in historical accounts and those reproduced by numerical modelling, for which we propose alternative interpretations of the historical record. Unfortunately, given the minimal details available about the eruption, this discordance is unlikely to be resolved, even when geological studies are possible. However, a valuable benefit of the probabilistic modelling approach presented here is that it highlights the likely direction of tephra dispersal and deposition during a future eruption of Makaturing, supporting rapid tephra hazard assessment in the event of future unrest.

Long-Term Probabilistic Volcanic Hazard Assessment Using Open and Non-open Data: Observations and Current Issues

Probabilistic volcanic hazard assessment (PVHA) has become the paradigm to quantify volcanic hazard over the last decades. Substantial aleatory and epistemic uncertainties in PVHA arise from complexity of physico-chemical processes, impossibility of their direct observation and, importantly, a severe scarcity of observables from past eruptions. One factor responsible for data scarcity is the infrequency of moderate/large eruptions; other factors include lack of discoverability and accessibility to volcanological data. Open-access databases can help alleviate data scarcity and have significantly contributed to long-term PVHA of eruption onset and size, while are less common for data required in other PVHA components (e.g. vent opening). Making datasets open is complicated by economical, technological, ethical and/or policy-related challenges. International synergies (e.g. Global Volcanism Program, WOVOdat, Global Volcano Model, EPOS) will be key to facilitate the creation and maintenance of open-access databases that support Next-Generation PVHA. Additionally, clarification of some misconceptions about PVHA can also help progress. Firstly, PVHA should be understood as an expansion of deterministic, scenario-based hazard assessments. Secondly, a successful PVHA should sometimes be evaluated by its ability to deliver useful and usable hazard-related messages that help mitigate volcanic risk. Thirdly, PVHA is not simply an end product but a driver for research: identifying the most relevant sources of epistemic uncertainty can guide future efforts to reduce the overall uncertainty. Broadening of the volcanological community expertise to statistics or engineering has already brought major breakthroughs in long-term PVHA. A vital next step is developing and maintaining more open-access datasets that support PVHA worldwide.

First Speleothem Evidence of the Hiera Eruption (197 BC), Santorini, Greece

ABSTRACT Speleothems are useful in detecting past geoenvironmental events. Variations in trace element concentrations may constitute a diagnostic of volcanic eruptions, enabling both dating and environmental impact assessment. This work attempts to detect possible ‘signatures’ of past volcanic eruptions in speleothems from Zoodochos Pigi cave on Santorini. Higher-than-usual concentrations of elements and minerals (e.g. barium and monazite respectively) exotic to typical speleothem chemistry in a band within a flowstone retrieved from the cave were revealed through SEM-EDS and XRD analyses and thought to be of volcanic origin. By chance, charcoal trapped in the said speleothem band allowed dating to establish the timing of the volcanic event. The radiocarbon date pointed towards the historically documented Hiera eruption, the earliest of a series of volcanic eruptions that postdate the Minoan eruption. The Hiera eruption, although less violent than the Minoan eruption, signallised the recrudescence of intracaldera activity which culminated in the formation of Palea Kameni (197 BC) with palpable effects on the regional environment. The interpretation of the results presented here, i.e. geochemical analysis on speleothems and radiocarbon dating, are cross-correlated with the well-documented timeline of eruptions of Santorini and ancient literature.