Major Eruptive Events Research Articles

Lithostratigraphy of the ignimbrite-dominated Miocene Bükk Foreland Volcanic Area (Central Europe)

This study documents the volcanic evolution of the Miocene silicic Bükk Foreland Volcanic Area (BFVA), Northern Hungary (Central Europe) at an event-scale. The BFVA is a deeply eroded and dissected volcanic field dominated by multiple, several 10-m thick, valley-filling silicic ignimbrite units, which are chemically and texturally very similar to each other. Hence, establishing lateral correlation is a real challenge due to the sporadic and small-scale outcrops and lack of stratotypes. Detailed field observations allowed us to identify eleven lithological members including fourteen eruption events and establish a nearly complete lithostratigraphic correlation between fifteen outcrops across the BFVA. Primary pyroclastic material of each member was sampled, and volcanic glass was analyzed for major and trace element composition. The geochemical results confirm the field-based classification of the members and enable the correlation of distinct outcrops. The major and trace element composition of the glassy pyroclasts of each member of the BFVA served as basis to create a field-wide chemical reference database for regional correlational studies. Here, a new lithostratigraphic classification scheme consisting of one formation and eleven members is presented, which reflects the challenges unraveling the stratigraphy of ancient volcanic terrains. The field-based event-scale lithostratigraphy of the BFVA suggests a wet, partly sea-covered depositional environment in the close vicinity of the eruption centers providing favorable conditions to ‘fuel’ silicic explosive phreatomagmatism. On the contrary, paleosol horizons formed after almost each major eruption event or sequence suggests an overall near-coast terrestrial environment for the BFVA, where the emplacement of the pyroclastic material occurred.

Strategic Study for the Development of Solar Physics in Space

Solar physics specializes the study of the fundamental processes occurred in the Sun and their influences on the interplanetary space. It deals with detailed measurements that are possible only for our closest star which is a natural plasma laboratory with multi-scale processes taking place. In addition, solar activities have a high impact on the space weather and habitability of the Earth, major solar eruptive events such as solar flare and coronal mass ejection have harmful effects on communication systems, satellites, power grid, and so forth. The study of the Sun not only helps us to understand the universe, the solar-terrestrial relationship, and the planetary habitability, but also serves national strategies in space and aerospace security. In the 21st century, there has been considerable progress in solar physics due to the development of detecting the Sun from space. In this paper, recent space exploration development trends of solar physics are examined both at home and abroad, key fields of the future space exploration development of solar physics in China are summarized, the disciplinary layout is optimized, and high-quality development of solar physics is promoted.

Eruptive history of Mt. Fuji over the past 8000 years based on integrated records of lacustrine and terrestrial tephra sequences and radiocarbon dating

Reliable records of past volcanic activities are essential for assessing future eruption probabilities and establishing effective volcanic disaster mitigation plans. We integrated the lacustrine and terrestrial sequences of tephra deposits at the northeastern foot of Mt. Fuji based on high-resolution radiocarbon (14C) dating to elucidate its eruptive history over the past 8000 years. Accurate chronologies of 29 tephra layers in the Lake Yamanaka sediments (core YA-1) were determined using the age-depth model of the 14C of bulk organic matter after variability correction of lake reservoir ages. The following ages were compared to those of major tephra deposits in the proximal trench section (MF20-01) and in the literature. From ∼7300 to ∼3200 cal yr BP, four tephra layers in core YA-1 (i.e., YA-T1, 2, 7, and 10) were likely correlated with the scoria fall deposits S-3, 5, 6, and 10 respectively, as reported in the outcrops near the lake. The core also features six undetected eruptions from ∼5050 to ∼3900 cal yr BP, demonstrating the advantages of lake sediments proximal to the volcano in identifying previously undetected eruptions. After ∼3200 cal yr BP, five tephra layers in core YA-1, ranging from ∼2900 to ∼1600 cal yr BP (YA-T11, 12, 14, 20, and 22), showed similar age ranges as the major tephra layers in MF20-01 (IY5, 8, 11, 25, and 26), with identical lithological characteristics and stratigraphic orders. This suggests that the tephra sequence in the trench section positively reflects the major eruptive events over the past 2900 years, providing a basis for the comprehensive reconstruction of volcanic eruption histories in the region.

Magnetic cloud prediction model for forecasting space weather relevant properties of Earth-directed coronal mass ejections

Context.Coronal mass ejections (CMEs) are major eruptive events on the Sun that result in the ejection of large-scale magnetic clouds (MCs) in interplanetary space, consisting of plasma with enhanced magnetic fields whose direction changes coherently when measured in situ. The severity of CME-induced geomagnetic perturbations and space weather impacts depends on the direction and strength of the interplanetary magnetic field (IMF), as well as on the speed and duration of the passage of the magnetic cloud associated with the storm. The coupling between the heliospheric environment and Earth’s magnetosphere is strongest when the IMF direction is persistently southward (i.e. negativeBz) for a prolonged period. Predicting the magnetic profile of such Earth-directed CMEs is therefore critical for estimating their space weather consequences; this remains an outstanding challenge, however.Aims.Our aim is to build upon and integrate diverse techniques towards the development of a comprehensive magnetic cloud prediction (MCP) model that can forecast the magnetic field vectors, Earth-impact time, speed, and duration of passage of solar storms.Methods.The configuration of a CME is approximated as a radially expanding force-free cylindrical structure. Combining near-Sun geometrical, magnetic, and kinematic properties of CMEs with the probabilistic drag-based model and cylindrical force-free model, we propose a method for predicting the Earth-arrival time, propagation speed, and magnetic vectors of MCs during their passage through 1 AU. Our model is able to predict the passage duration of the storm without recourse to computationally intensive time-dependent dynamical equations.Results.Our method is validated by comparing the MCP model output with observations of ten MCs at 1 AU. In our sample, we find that eight MCs show a root mean square (rms) deviation smaller than 0.1 between the predicted and observed magnetic profiles, and the passage durations of seven MCs fall within the predicted range.Conclusions.Based on the success of this approach, we conclude that predicting the near-Earth properties of MCs based on an analysis and modelling of near-Sun CME observations is a viable endeavour with potential applications for the development of early-warning systems for space weather and enabling mitigation strategies.

Multi-parametric study of an eruptive phase comprising unrest, major explosions, crater failure, pyroclastic density currents and lava flows: Stromboli volcano, 1 December 2020–30 June 2021

Open conduit volcanoes like Stromboli can display elusive changes in activity before major eruptive events. Starting on December 2020, Stromboli volcano displayed an increasing eruptive activity, that on 19 May 2021 led to a crater-rim collapse, with pyroclastic density currents (PDCs) that spread along the barren NW flank, entered the sea and ran across it for more than 1 km. This episode was followed by lava flow output from the crater rim lasting a few hours, followed by another phase of lava flow in June 2021. These episodes are potentially very dangerous on island volcanoes since a landslide of hot material that turns into a pyroclastic density current and spreads on the sea surface can threaten mariners and coastal communities, as happened at Stromboli on 3 July and 28 August 2019. In addition, on entering the sea, if their volume is large enough, landslides may trigger tsunamis, as occurred at Stromboli on 30 December 2002. In this paper, we present an integration of multidisciplinary monitoring data, including thermal and visible camera images, ground deformation data gathered from GNSS, tilt, strainmeter and GBInSAR, seismicity, SO2 plume and CO2 ground fluxes and thermal data from the ground and satellite imagery, together with petrological analyses of the erupted products compared with samples from previous similar events. We aim at characterizing the preparatory phase of the volcano that began on December 2020 and led to the May–June 2021 eruptive activity, distinguishing this small intrusion of magma from the much greater 2019 eruptive phase, which was fed by gas-rich magma responsible for the paroxysmal explosive and effusive phases of July–August 2019. These complex eruption scenarios have important implications for hazard assessment and the lessons learned at Stromboli volcano may prove useful for other open conduit active basaltic volcanoes.

Re-colonization of hostile environments by benthic foraminifera: an example from Montserrat, Lesser Antilles Volcanic Arc

The Soufrière Hills Volcano, on the island of Montserrat, has an eruption history spanning over 2 million years. During this time the volcano has undergone multiple eruptions with intervening periods of low activity or dormancy. The most recent activity began in 1995 and has seen a series of major eruptive events. One of the most recent of these, and the focus of this study, occurred on the 20th May 2006. This major dome collapse produced 90 million m3 of volcanic material in only 3 hours, propelling ash clouds through the air and pyroclastic flows down the side of the volcano and into the sea. In this study of benthic foraminifera, cores from four sites off-shore Montserrat are analysed, including those collected from a location within the path of the 2006 ash cloud, around 10 km west of the Montserrat coast. In this area, one core contained 6-7 cm of ash overlying hemipelagic sediments. Volcanic ash is present in two distinct layers, one 3 cm layer produced by the 2006 eruption and the other, 3-4 cm layer, from an earlier eruption in 2003. Other cores were collected from areas unaffected by recent ash fall deposits and provide a base line for comparisons within the affected areas. To the east and south-east of Montserrat there is a different situation as this is the direction of travel of massive pyroclastic flows down the Tar Valley and the impact on the sea floor is more dramatic. There are also two extinct volcanic centres that allow the investigation of sea floor re-colonization on different time scales. The sites to the west of Montserrat record rapid colonization by benthic foraminifera of opportunistic taxa, comparable to that seen near Mt Pinatubo in the South China Sea while the sites to the east record a slower pattern of re-colonization by a wider spectrum of taxa, similar to that recorded at Deception Island in the Southern Ocean, with different benthic taxa performing the pioneering role.

Correlating volcanic dynamics and the construction of a submarine volcanogenic apron: An example from the Badenian (Middle Miocene) of North-Eastern Hungary

This work studies a submarine volcanogenic apron forming the Nagyhársas Andesite Formation (Badenian – Middle Miocene) in the Mátra Mountains (North-Eastern Hungary), with the aim to identify volcanic processes, from the sedimentary bed scale to the architecture of the whole apron. Fieldwork has been carried out in two different localities (Tar and Sámsonháza villages), where eighteen logs have been measured and correlated, reconstructing the stratigraphic variations of the sedimentary beds and the volcano-sedimentary architectures of the proximal and distal part of the volcanogenic apron. Fifty-two samples have been collected, cut into standard thin sections and petrographically studied to support the interpretation of mechanisms that accumulated the volcanogenic detritus in the submarine realm, as well as to identify the possible volcanic source and how it interacted with the marine environment. The results allow for the first time to underline the importance of a correct interpretation of volcanongenic deposits in the constrain of regional sea level variations, and to discuss the role of active volcanic edifices in shaping the proximal and distal sedimentary architecture of volcanogenic aprons. In proximal areas, the correlation between eruptive cycles and excavation-infill cycles of apron channels suggests that major eruptive events are responsible for channel excavation, whereas minor eruptive events contributed to the infilling of those architectures. In distal areas, the large supply of volcanogenic sediments cannibalizes the sedimentary system, temporally inhibiting the progradation of carbonate platforms nearby the apron offshoots, as well as allows the bypass of topographic barrier (e.g., ridges) favouring mechanisms of sediment spill-over in areas where otherwise sedimentation would be prevented.

Evolution of force‐free field parameter in active regions with major eruptive events

Using a nonlinear force‐free field (NLFFF) method to extrapolate photospheric magnetic fields, we compute the force‐free field parameter (α), which is a measure of torsion of the magnetic field lines. We calculated the α parameter for 62 active regions that produced major eruptive events in solar cycle 24. We verified statistically how the 62 studied active regions obey the hemispheric rule of helicity. In agreement with previous studies, we found that 67% of active regions located in the northern hemisphere have a negative sign for the global alpha parameter αg, and 69% of the active regions situated in the southern hemisphere have a positive sign. We have identified and analyzed five cases of evolution of αg at times when eruptive phenomena occurred in the selected active regions. We find that 52% of cases show an increase of torsion during flares, while only 22% show a decrease. This shows that increasing torsion plays an important role in flare ignition. For the other cases, a definitive conclusion cannot be reached because of multiple variations.

Insight on magma evolution and storage through the recent eruptive history of Cotopaxi Volcano, Ecuador

Cotopaxi is a stratovolcano in the Northern Volcanic Zone of the Andes, and has a history of bimodal volcanism, alternating between rhyolite and andesite. With Cotopaxi reawakening in 2015 after 138 years of no major eruptions (>VEI 1–2), the question of what is occurring beneath the surface becomes especially poignant in the recent past. This work characterizes the mineralogy and geochemistry of the recent eruptive products of Cotopaxi, with emphasis on the two pulses of the 1877 eruption. Over the past 500 years Cotopaxi has had five major eruptive events (VEI 3–4), which occurred in 1532, 1742, 1744, 1768, and 1877, and included regional tephra fallout, pyroclastic scoria flows and surges, as well as lahars. After the initial pulse of the 1877 eruption and the subsequent lahars, a second pulse of magma produced pyroclastic density currents, containing scoria clasts up to 1 m in diameter. All samples collected from these eruptions are basaltic-andesite to andesite (56–59 wt % SiO2), with a mineral assemblage composed of pl + opx + cpx + mag ± ol. Plagioclase from all samples range from An47 to An78 and show both normal and reverse zoning. Pyroxenes occur as augite and enstatite and do not exhibit significant zoning. The presence of disequilibrium textures such as zoned plagioclase and enclaves with fluidal margins with host indicate that magma mingling/mixing plays a role in magma genesis. The very similar petrologic characteristics of these deposits suggests that they were formed in a relatively long-lived magma system that experienced moderate differentiation and magma replenishment between eruptions. Fractional crystallization modeling shows that crystallization of plagioclase (11.7%) + pyroxene (3.4%) + amphibole (4.6%) + magnetite (1.1%) + apatite (0.2%) can produce the observed compositional variation. However, some of the variation can be explained by mixing, thus we conclude that both differentiation processes occurred. Thermobarometric data indicate that magma storage occurred at temperatures of ∼1017 °C and pressures ranging from 0.215 GPa (during the 1877 eruption) to 0.619 GPa (during the 1532 eruption), which is equivalent to depths of 7 and 21 km (±9 km), respectively.

Pollen analysis and tephrochronology of a MIS 13 lacustrine succession from Eastern Sabatini Volcanic District (Rignano Flaminio, central Italy)

Diatomite deposits in the Sabatini Volcanic District (central Italy) represent valuable archives to investigate both Middle Pleistocene vegetation dynamics and geochemistry of proximal products of volcanic eruptions, which provide crucial geochronological markers for a large region of Southern Europe. We present a new pollen record from a diatomite deposit at Rignano Flaminio, attributed to MIS 13 based on two major eruptive events from Monti Sabatini: the Grottarossa Pyroclastic Sequence (513 ± 3 ka) and the Fall A unit (499 ± 3 ka). We also add insights into the geochemical and mineralogical composition of the proximal deposits of the Fall A tephra, whose products are found in several sites of the central Mediterranean. Our pollen record shows marked vegetation turnovers, reflecting changes in regional and global climate conditions, local environmental factors and ecological processes within refuge areas. The lower part of the record points to a forested environment dominated by both deciduous and evergreen broadleaved taxa, indicating wet and temperate climate conditions. This interval was punctuated by two phases of slight forest declines, where a general increase in Poaceae and Artemisia, coupled with the development of Ericaceae and evergreen Quercus communities, suggests the establishment of mediterranean-type climatic conditions with increased aridity. The upper part of the sequence shows the development of Abies and Pinus woodlands, reflecting a change towards cooler and possibly wetter climate. The pollen richness, accompanied by a fossil leaf of Laurus, confirms the role of the Sabatini Volcanic District as a Pleistocene biodiversity hot-spot and refuge area for many trees.

The Talili Pyroclastics eruption sequence: VEI 5 precursor to the seventh century CE caldera-forming event at Rabaul, Papua New Guinea

Studies of the products of the activity precursory to caldera-forming events are essential in revealing how caldera systems evolve in the prelude to climactic eruptions. Here, we investigate the deposits formed by the Talili Pyroclastics eruption sequence, which preceded the youngest major eruptive event, the seventh century CE (1400 BP) Rabaul Pyroclastics VEI 6 caldera-forming eruption, at Rabaul in northeastern Papua New Guinea. The Talili Pyroclastics deposits are essentially a bimodal (dacite-basalt) tephra sequence that was emplaced during the 2.8 ky leading to the Rabaul Pyroclastics eruption. The dominant activity during the Talili period, starting at 4200 BP, involved strong (up to VEI 5), water-modified explosive eruptions of dacite from intra-caldera vents. This activity generated > 4.4 km3 of unstratified, bedded and laminated fine-grained fall deposits, pyroclastic surges and a small ignimbrite. In addition, all three of the young stratovolcanoes on the eastern and northeastern fringes of Rabaul Caldera were active during the Talili era, producing > 0.7 km3 of basaltic scoria fall and flow deposits. The main phase of Talili era basalt production occurred at 4100 BP and involved sequential eruptions from two of the stratovolcanoes, Palangiangia and Kabiu. The sequence of dacitic Talili eruptives shows a progressive decline then late-stage increase in SiO2 contents, with corresponding changes in Fe2O3, MgO and CaO. Early and late products have compositions similar to those of the most-evolved products of the major eruptions at Rabaul (intermediate to high-SiO2 dacites), while middle-stage products are similar to those of the historical eruptions (lower-SiO2 dacites and andesites). The basaltic eruptives have three different compositions, attributed to three different (stratovolcano) sources. There is no evidence of mixing or mingling of basalt and dacite. However, andesitic scoria inclusions in the early-erupted dacitic ignimbrite represent mingling of andesitic and dacitic magmas. As with the Talili Pyroclastics, at least two other earlier tephra sequences at Rabaul probably resulted from phases of VEI 5 volcanism and directly underlie the deposits of major eruptions. This leads to the inference that cycles of escalating eruptive activity have prevailed prior to some of the major eruptions, and suggests that the strength of volcanism at Rabaul may rise from the lower levels (maximum of VEI 4) evident since the Rabaul Pyroclastics event as the system moves towards the next major eruption.

Investigating the Magnetic Imprints of Major Solar Eruptions with SDO/HMI High-cadence Vector Magnetograms

Abstract The solar active region photospheric magnetic field evolves rapidly during major eruptive events, suggesting appreciable feedback from the corona. Previous studies of these “magnetic imprints” are mostly based on line of sight only or lower-cadence vector observations; a temporally resolved depiction of the vector field evolution is hitherto lacking. Here, we introduce the high-cadence (90 s or 135 s) vector magnetogram data set from the Helioseismic and Magnetic Imager, which is well suited for investigating the phenomenon. These observations allow quantitative characterization of the permanent, step-like changes that are most pronounced in the horizontal field component (B h ). A highly structured pattern emerges from analysis of an archetypical event, SOL2011-02-15T01:56, where B h near the main polarity inversion line increases significantly during the earlier phase of the associated flare with a timescale of several minutes, while B h in the periphery decreases at later times with smaller magnitudes and a slightly longer timescale. The data set also allows effective identification of the “magnetic transient” artifact, where enhanced flare emission alters the Stokes profiles and the inferred magnetic field becomes unreliable. Our results provide insights on the momentum processes in solar eruptions. The data set may also be useful to the study of sunquakes and data-driven modeling of the corona.

Duration and periodicity of kimberlite volcanic activity in the Lac de Gras kimberlite field, Canada and some recommendations for kimberlite geochronology

Establishing the emplacement ages and distribution pattern of Central Slave kimberlites has played a key role in diamond exploration within the Lac de Gras kimberlite field. Nonetheless, emplacement age information is lacking for approximately 80% of the known kimberlites in this field making the assessment of emplacement age patterns difficult. This study expands the number and geographic coverage of kimberlite emplacement ages within the Lac de Gras field to re-assess the absolute timing, duration, and possible number of pulses of kimberlite eruption. U–Pb perovskite ages for eight previously undated kimberlites and an additional thirteen kimberlites, which were previously dated by either the Rb–Sr or U–Pb methods, fall within the age range of 75–45Ma, as previously suggested for kimberlite magmatism in this area. We report the first Carboniferous age kimberlite in the Central Lac de Gras field – the Eddie kimberlite – with a U–Pb perovskite age of 321.0±3.0Ma. A compilation of 57 kimberlite emplacement ages from the central Lac de Gras field was evaluated using probability density and mixture modeling methods. Five short-duration (4–5Ma) periods of kimberlite magmatism are recognized at 48, 54, 61, 66 and 72Ma; the three younger pulses have been previously recognized and remain relatively unchanged. The 54Ma pulse represents the major kimberlite eruption event containing ~40% of the currently dated kimberlites in Lac de Gras field. A detailed evaluation of the temporal–spatial evolution of Lac de Gras kimberlites reveals that the oldest diamond-poor kimberlites (75–60Ma) were emplaced in the northern and eastern parts of the field whereas the younger (55–48Ma) economic kimberlites are concentrated in the center of the field.

Central Tibetan Meso-Tethyan oceanic plateau

We report the occurrences of the remnants of a Meso-Tethyan oceanic plateau, encompassing an area of ~ 2 × 10 5 km 2 in central Tibet. The plateau remnants include large volumes of pillow basalt formed largely by emergent to subaerial eruption, minor ultramafic intrusives and cumulates, exotic blocks of limestone, radiolarian chert, graywacke, and shale. Isotopic and paleontological dating suggest two major plateau eruptive events at 193–173 Ma and at 128–104 Ma, respectively. The basalts are characterized by enrichment of incompatible elements and a wide range of Sr–Nd isotope composition (initial ε Nd from –3.71 to + 7.9, initial 87 Sr/ 86 Sr from 0.703927 to 0.707618). The trace element and Sr–Nd isotopic data suggest that these basalts are of affinity with those from the Kerguelen and Tethyan plumes, indicative of a plume mantle upwelling origin with involvement of continental material. The wholesale obduction of the Meso-Tethyan oceanic plateau, along with the dismembered normal oceanic crustal fragments, over the Tibetan continental crust could have given rise to perhaps 2 km elevation of central Tibet during the Late Cretaceous. • Remnants of Meso-Tethyan oceanic plateau in central Tibet covers an area of ~ 2 × 10 5 km 2 . • Plateau remnants are dominated by basalt sections with a thickness of at least 13 km. • Twohree major plateau eruptive events occurred at 193–173 Ma, at 167–162 Ma, and at 128–104 Ma. • Basalts are enriched in incompatible elements, with a wide range of and heterogeneous in Sr–Nd isotopes. • Obduction of the oceanic plateau likely triggered a 2-km elevation of central Tibet.

Assessment of depositional ash loadings from the 2009 eruption of Mt. Redoubt

Volcanic ash deposited onto ice and snow in the Arctic has the potential to perturb the regional radiation balance by altering the surface reflectivity. In order to determine changes in surface albedo, loading fields of deposits must be quantified. Loading fields are defined as the total mass of ash deposited over an area. We assessed the areal extent and loading of ash deposits from the 2009 eruption of Mt. Redoubt using an Eulerian volcanic ash transport and dispersion model, Fall3D, combined with satellite and deposit observations. Because direct observations are often limited in remote Arctic regions, we devised a novel method for modeling ash deposit loading fields for the entire eruption based on best-fit parameters of a well-studied eruptive event. The major land-depositing eruptive events (events 2–6 on March 23–24) were chosen for analyses. Realistic ranges of model parameters were selected based on the well-described event 5 (March 23) and were estimated for other events. The model results were validated against NASA A-train satellite data and field measurements reported by the Alaska Volcano Observatory. Overall, good to moderate agreement was found. A total cumulative deposit area of 3.7×106km2 was produced, and loadings ranged from ~7000±3000gm−2 near the vent to <0.1±0.002gm−2 on the outer margins of the deposits. Spatial gradients of total ash loading along a cross-section extending from Mt. Redoubt to ~600km revealed event 5 contributed most to the total loading from 0 to 200km, followed by events 3, 4, 6, and 2. Ash loading histories for total deposits showed that fallout time along the cross-section for each of events 2–6 ranged from ~5–17h. Our deposit loading results suggest that ash from short-duration events can produce regionally significant deposits hundreds of kilometers from the volcano, with the potential of significantly modifying albedo over wide regions of ice and snow covered terrain.

A major solar eruptive event in July 2012: Defining extreme space weather scenarios

AbstractA key goal for space weather studies is to define severe and extreme conditions that might plausibly afflict human technology. On 23 July 2012, solar active region 1520 (~141°W heliographic longitude) gave rise to a powerful coronal mass ejection (CME) with an initial speed that was determined to be 2500 ± 500 km/s. The eruption was directed away from Earth toward 125°W longitude. STEREO‐A sensors detected the CME arrival only about 19 h later and made in situ measurements of the solar wind and interplanetary magnetic field. In this paper, we address the question of what would have happened if this powerful interplanetary event had been Earthward directed. Using a well‐proven geomagnetic storm forecast model, we find that the 23–24 July event would certainly have produced a geomagnetic storm that was comparable to the largest events of the twentieth century (Dst ~ −500 nT). Using plausible assumptions about seasonal and time‐of‐day orientation of the Earth's magnetic dipole, the most extreme modeled value of storm‐time disturbance would have been Dst = −1182 nT. This is considerably larger than estimates for the famous Carrington storm of 1859. This finding has far reaching implications because it demonstrates that extreme space weather conditions such as those during March of 1989 or September of 1859 can happen even during a modest solar activity cycle such as the one presently underway. We argue that this extreme event should immediately be employed by the space weather community to model severe space weather effects on technological systems such as the electric power grid.

ON THE ROLE OF ROTATING SUNSPOTS IN THE ACTIVITY OF SOLAR ACTIVE REGION NOAA 11158

We study the role of rotating sunspots in relation to the evolution of various physical parameters characterizing the non-potentiality of the active region NOAA 11158 and its eruptive events using the magnetic field data from the Helioseismic and Magnetic Imager (HMI) and multi-wavelength observations from the Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO). From the evolutionary study of HMI intensity and AIA channels, it is observed that the AR consists of two major rotating sunspots one connected to flare-prone region and another with CME. The constructed space-time intensity maps reveal that the sunspots exhibited peak rotation rates coinciding with the occurrence of the major eruptive events. Further, temporal profiles of twist parameters, viz., average shear angle, $\alpha_{\rm av}$, $\alpha_{\rm best}$, derived from HMI vector magnetograms and the rate of helicity injection, obtained from the horizontal flux motions of HMI line-of-sight magnetograms, corresponded well with the rotational profile of the sunspot in CME-prone region, giving predominant evidence of rotational motion to cause magnetic non-potentiality. Moreover, mean value of free-energy from the Virial theorem calculated at the photospheric level shows clear step down decrease at the on set time of the flares revealing unambiguous evidence of energy release, intermittently that is stored by flux emergence and/or motions in pre-flare phases. Additionally, distribution of helicity injection is homogeneous in CME prone region while it is not and often changes sign in flare-prone region. This study provides clear picture that both proper and rotational motions of the observed fluxes played significant role to enhance the magnetic non-potentiality of the AR, leading to favorable conditions for the observed transient activity.

Sequence of the 1895 eruption of the Zao volcano, Tohoku Japan

The most recent major eruption event of the Zao volcano comprised a series of phreatic eruption episodes on 15 and 19 February, 22 August, and 27–28 September 1895, with several precursory vulcanian eruptions during February–July 1894. All were generated at the Okama crater lake located inside the Umanose caldera. The eruption products consist mainly of hydrothermally altered ash with altered blocks, except for ash from 1984. The eruption deposits of 1895 are divided lithologically into six layers (1–6). Comparison of the document with the lithofacies of deposits shows that layers 1, 2, 3–4, and 5–6 were correlated respectively with eruption episodes of 15 February (episode 1), 19 February (episode 2), 22 August (episode3), and 27–28 September (episode 4). During these four episodes, ca. 0.5%, 0.5%, 1.5%, and 98% of the total mass of the products had been discharged. Based on lithologic, stratigraphic, granulometric, and component analyses and on distributional features for these layers, the following depositional mechanisms were inferred. Layers 1, 3, and 4 were formed mainly from their related small pyroclastic density currents, whereas layer 2 resulted mainly from a small pyroclastic fall. In contrast, layers 5 and 6 are larger-scale near-vent pyroclastic fall deposits from ash clouds and eruption clouds, which might have included some juvenile fragments. The three early episodes in 1985 led to the climactic episode of 27–28 September. Furthermore, the andesitic magma chamber at <3kb depth, which caused the 1894 vulcanian eruptions, became a hydrothermal alteration source for the 1895 erupted materials. The chamber was re-activated before 1895 eruption by injection of basaltic magmas from greater depth. The injection reached maximum at the climactic event. The inferred course of that series of eruption episodes provides useful information to predict future volcanic phreatic-type eruptions at this volcano.

Magnetic Connectivity Between Active Regions 10987, 10988, and 10989 by Means of Nonlinear Force-Free Field Extrapolation

Extrapolation codes for modelling the magnetic field in the corona in cartesian geometry do not take the curvature of the Sun's surface into account and can only be applied to relatively small areas, \textit{e.g.}, a single active region. We apply a method for nonlinear force-free coronal magnetic field modelling of photospheric vector magnetograms in spherical geometry which allows us to study the connectivity between multi-active regions. We use vector magnetograph data from the Synoptic Optical Long-term Investigations of the Sun survey (SOLIS)/Vector Spectromagnetograph(VSM) to model the coronal magnetic field, where we study three neighbouring magnetically connected active regions (ARs: 10987, 10988, 10989) observed on 28, 29, and 30 March 2008, respectively. We compare the magnetic field topologies and the magnetic energy densities and study the connectivities between the active regions(ARs). We have studied the time evolution of magnetic field over the period of three days and found no major changes in topologies as there was no major eruption event. From this study we have concluded that active regions are much more connected magnetically than the electric current.

Events in the Precambrian history of the Earth: Challenges in discriminating their global significance

This paper discusses geological events with an approximately global preservational scale which can aid inter-cratonic correlations and contribute to postulates of supercontinents for a set of chosen Precambrian cratons. The chronological scale of such events is highly variable, and most event types detailed (supercontinent-, mantle plume-, orogenic-, chemostratigraphic-, glacial events and major unconformities) have durations concomitant with the large-scale interaction of mantle thermal and plate tectonic processes that were largely responsible for their genesis, i.e. 10s to 100s of millions of years. Geologically instantaneous events of global compass (e.g., impact or major eruptive events) provide important chronological markers for interpreting the longer term events. The same interplay of tectono-thermal geodynamic processes that drives the evolution of the Earth and the operation of its supercontinent cycles is also, ultimately, responsible for and of comparable duration to first- and second-order sequence stratigraphic cyclicity. This paper thus serves to introduce these concepts and discuss the problems in their application to specific Precambrian cratons, in relation to the aim of this special issue, of providing a set of accommodation curves for many of these ancient crustal terranes.