Increase In Volcanic Activity Research Articles

HYPOCENTER DISTRIBUTION ANALYSIS OF SINABUNG VOLCANO ERUPTION IN 2021 USING GEIGER'S WITH ADAPTIVE DAMPING (GAD) METHOD

Sinabung Volcano is located in the Karo Highlands, Karo Regency, North Sumatra, Indonesia, with a peak of 2460 meters above sea level. This volcano experienced an increase in volcanic activity in the April-October 2021 period, so it is necessary to analyse volcanic seismicity to determine the hypocenter distribution of the volcano. This study aims to determine the hypocenter distribution and classification of volcanic earthquake types based on seismogram recording data of Sinabung Volcano at four stations, namely LKW, BGR, MDD and SGR stations. The method used in this research is Geiger's method with adaptive damping (GAD) to determine the distribution of hypocenters. The results showed that the hypocenter distribution gathered below the crater centre with depths from 0.172 km to 7.139 km. The determination of the hypocenter distribution of volcanic earthquakes is expected to provide information on the depth of the earthquake to determine the movement of magma and the characteristics of events that occur during the pre-eruption process of Sinabung Volcano so that this data can be used for mitigation decision making when there is an increase in the activity of Sinabung Volcano.

Timing of Quaternary volcanism and its relationship with tectonics in the central segment of the Ecuadorian Andes

The unusually high number of volcanoes in the Ecuadorian Arc, located in the deformation zone of the continental North Andean Sliver, coincides with the projection of the major oceanic structures observed in the Nazca Plate, such as the Carnegie Ridge and the Grijalva fracture zone. Although the relationship between this tectonic setting and volcanism has been widely discussed in the literature, their temporal relationship has not been thoroughly investigated due to the lack of geochronological data. We present here 20 new KAr and 2 40Ar/39Ar ages obtained for 7 volcanoes of the central segment of the Ecuadorian arc, which together with previous data show that volcanism in this area started at ∼1.3 Ma. A notable increase in volcanic activity occurred since ∼0.6 Ma, when the formation of a dozen volcanoes occurred in a relatively small area of the central segment. While this arrangement of volcanoes, here referred to as a “volcanic cluster”, appears to be controlled by crustal tectonic structures, the order of onset of these volcanoes and their eruptive activity does not show clear migration patterns over time. However, the presence of older volcanoes in the north of the central segment suggests a possible southward extension of volcanism between ∼1.3 and ∼ 0.6 Ma. Finally, based on the cumulative bulk volumes calculated for the volcanic edifices over time, we infer that the magmatic productivity rate has been roughly constant during the last ∼550 kyr in this area.

Identification of Geological Structure Based on Gravity Method in Tangkuban Parahu Volcano, Bandung, Indonesia

Tangkuban Parahu Volcano, located in Cikahuripan, Lembang, West Bandung Regency, West Java, Indonesia, has a geothermal potential. However, this potential is accompanied by geohazard risks, one of which is a volcanic eruption that can interfere with the development of geothermal potential. On February 12, 2022, there was a gust of volcanic gas from Ratu Crater, indicating an increase in volcanic activity after an eruption in 2019. Based on the geological map of Tangkuban Parahu/Sunda Volcano Complex, it is estimated that there is a fault structure in a northwest-southeast direction, where if a volcanic eruption occurs, it will cause greater deformation because it cuts through Ratu Crater. Further studies with geophysical methods are needed to estimate the fault structure. The study of the subsurface geological structure of Tangkuban Parahu Volcano was carried out using the gravity method by studying variations in the gravitational field on the earth’s surface to determine differences in rock density. The Complete Bouguer Anomaly (CBA) value from the gravity method at Tangkuban Parahu Volcano shows 68 – 73 mGal, and residual anomaly values ranged from -0.95 to 0.67 mGal. The negative residual anomaly value between -0.95 to 0 mGal shows the weak zone due to volcanism in the crater. On the other hand, high residual anomaly values ranging from 0 to 0.67 mGal are interpreted as the influence of Lava 1 Tangkuban Parahu (Tl1). Analysis using First Horizontal Derivative (FHD) and Second Vertical Derivative (SVD) shows a fault structure trending Northwest – Southeast, which can be a way out of the accumulation of high-pressure water vapor due to volcanic activity.

Paleoenvironment of the Cerro Negro Formation (Aptian, Early Cretaceous) of Snow Island, Antarctic Peninsula.

A study of macro and microfacies, palynoflora and palynofacies of the non-marine Cerro Negro Formation at President Head Peninsula, Snow Island, northwest of the Antarctic Peninsula, was developed. Two assemblages were recognized: Palynofacies assemblage 1 (P1) at the base of the section with a dominance of fern spores and conifer pollen grains, and facies association consisting of a clastic layer, with the predominance of mudstones; and Palynofacies assemblage 2 (P2) at the top of the section, with remarkable abundance of AOM/Pseudoamorphous particles, associated with facies that includes tuffs. The complete section shows in some levels the presence of freshwater algae and translucent phytoclasts. The integrated data characterizes a fluvial-lacustrine environment, what is reinforced by the occurrence of freshwater algae (Botryococcus) in some levels of P1 and P2. We could verify an increase in volcanic activity towards the top of the section that apparently has played an important role in the collapse of the palynoflora. The occurrence of the spore species Muricingulisporis annulatus, Sotasporites elegans, S. triangularis, Foraminisporis wonthaggiensis, and F. asymmetricus in the Cerro Negro Formation allows the correlation with sections in South America and Australia, suggesting an Aptian age for these deposits.

Scientific Basis and Geophysical Consequences of Geomagnetic Reversals and Excursions: A Fundamental Statement

Convection in Earth’s georeactor sub-shell is responsible for generating the geomagnetic field and for maintaining the critical balances necessary for stable sub-core nuclear fission. External factors capable of disrupting sub-shell convection are trauma at Earth’s surface, for example by meteorite impact, and electrical energy transfer via Faraday’s electromagnetic induction into the georeactor by changes in the solar wind or in the magnetospheric ring current. Reduced sub-shell convection not only leads to decreased geomagnetic field intensity, but to increased uranium settling out into the sub-core where it undergoes uncontrolled nuclear fission until sub-shell convection is reestablished. Periods of uncontrolled georeactor nuclear fission are responsible for causing geophysical phenomena at Earth’s surface that are associated with geomagnetic reversals and excursions. Anticipated consequences of sub-shell convection collapse include increases in volcanic activity, increases in the number and intensity of earthquakes, warming of the oceans, and diminishment of atmospheric convection resulting in global warming at the surface. The most worrisome potentiality is triggering the eruption of the Yellowstone super-volcano. Changes in solar wind flux, too small to cause geomagnetic field collapse, however, may cause increases in earthquakes and volcanic eruptions. The understanding described here potentially provides a basis for the development of earthquake and volcanic eruption prediction methodologies.

Adaptive classification using incremental learning for seismic-volcanic signals with concept drift

The accurate labeling of the volcanic earthquake signals is a crucial task in order to estimate the increase in volcanic activity (among other parameters), which contributes to determine a state of volcanic unrest (as a possible precursor of an eruption). Several automatic classification approaches have been proposed in different computer science areas in order to complement the exhaustive human task of manually labeling volcano-seismic events. However, most of these approaches have been designed under the assumption of stationarity; that is, by discarding the changing nature of the volcanic phenomenon that evolves over time. In this work, an adaptive classification strategy based on incremental learning is proposed, which identifies and learns concept drifts of data streams coming from seismic recordings. The proposed strategy uses a classifier ensemble in order to handle recurrent states and classifies data even while true labels are not yet available. Unlike usual experimental protocols in the state–of–the–art, we carried out experiments with seismic data from Villarrica volcano, considering the chronological order of the data during a long period (more than 4 years of registration) to achieve the detection of drifts. The results show that the proposed classification strategy satisfactorily counteracts the changes, in contrast to standard classifiers trained within a traditional learning scheme. The proposed strategy keeps a stable classification accuracy and achieves a reduction of up to 0.28 of the absolute error in episodes of abrupt changes.

Near-real-time volcanic cloud monitoring: insights into global explosive volcanic eruptive activity through analysis of Volcanic Ash Advisories

Understanding the location, intensity, and likely duration of volcanic hazards is key to reducing risk from volcanic eruptions. Here, we use a novel near-real-time dataset comprising Volcanic Ash Advisories (VAAs) issued over 10 years to investigate global rates and durations of explosive volcanic activity. The VAAs were collected from the nine Volcanic Ash Advisory Centres (VAACs) worldwide. Information extracted allowed analysis of the frequency and type of explosive behaviour, including analysis of key eruption source parameters (ESPs) such as volcanic cloud height and duration. The results reflect changes in the VAA reporting process, data sources, and volcanic activity through time. The data show an increase in the number of VAAs issued since 2015 that cannot be directly correlated to an increase in volcanic activity. Instead, many represent increased observations, including improved capability to detect low- to mid-level volcanic clouds (FL101–FL200, 3–6 km asl), by higher temporal, spatial, and spectral resolution satellite sensors. Comparison of ESP data extracted from the VAAs with the Mastin et al. (J Volcanol Geotherm Res 186:10–21, 2009a) database shows that traditional assumptions used in the classification of volcanoes could be much simplified for operational use. The analysis highlights the VAA data as an exceptional resource documenting global volcanic activity on timescales that complement more widely used eruption datasets.

The mid-Tournaisian (Early Carboniferous) anoxic event in the Laurussian shelf basin (Poland): An integrative approach

A wide range of proxies (organic and inorganic geochemistry, gamma-ray spectrometry, microfacies, framboidal pyrite analysis) were applied in order to decipher changes in depositional conditions during the mid-Tournaisian anoxic event, referred to as the Lower Alum Shale Event (LASE) in the Polish part of the Laurussia basin. The LASE part of the section, unlike older Tournaisian deposits, is characterised by high concentrations of isorenieratane, palaeorenieratane, and their diagenetic derivatives, the occurrence of 2-methyl-3-iso-butyl-maleimides, and high values of the sterane-to-hopane ratio. The predominance of tiny pyrite framboids, inorganic data such as low values of the Th/U and high values of the Corg/P and V/Cr ratios, and generally higher enrichments of redox-sensitive metals such as U, V, Mo, Pb, and Zn and depletion in Mn, all suggest anoxic/euxinic conditions on the sea-bottom. The results of our investigations, especially Co, Mn, Cd, and Mo distribution patterns, demonstrate that enhanced primary productivity in the water column was responsible for a high degree of organic carbon burial rather than preservation in restricted conditions on the seafloor. This elevated productivity may have been generated by the upwelling of nutrient-rich deep water, an increase in volcanic activity and volcanogenic oceanic fertilisation, or both. Volcanically driven mid-Tournaisian climatic changes (warming), as manifested by high Zr concentrations and Hg anomalies, may have been responsible for the deglaciation of Gondwana resulting in the global crenulata transgression.The global rise in sea level and high level of organic productivity were responsible for the development of anoxic conditions and the halt of carbonate production, as reflected by drastic changes of facies not only in the sections investigated, but in many other parts of the world as well.

A new high-resolution stratigraphic and palaeoenvironmental record spanning the End-Permian Mass Extinction and its aftermath in central Spitsbergen, Svalbard

Research on the Permian-Triassic boundary (PTB) along the northern margins of Pangaea (exposed today in the Arctic region) has been heavily reliant on field observations, where data resolution was consequently determined by outcrop condition and accessibility. Core drilling in central Spitsbergen allowed for a near-complete recovery of two ~90 m cores through the PTB. Analyses of the core and nearby outcrops include stratigraphic logging and sampling, XRF scanning, petrography, biostratigraphy, isotope geochemistry, and geochronology. The First Appearance Datum (FAD) of H. parvus in Svalbard places the base of the Triassic ca. 4 m above the base of the Vikinghøgda Formation, and ca. 2.50 m above the End-Permian Mass Extinction (EPME) and its associated sharp negative δ13C. The PTB therefore falls within the Reduviasporonites chalastus Assemblage Zone in Svalbard. Precise U-Pb TIMS dating of two zircon crystals in a tephra layer just above the first documented Hindeodus parvus in Svalbard gives an age of 252.13 ± 0.62 Ma. High-resolution palaeoenvironmental proxies, including Si/kcps (kilo counts per second), Zr/Rb, K/Ti, Fe/K, and V/Cr, indicate a transition towards a more arid climate in the earliest Triassic, contemporaneous with prolonged bottom-water dysoxic/anoxic conditions, following an increase in volcanic activity in the Late Permian. Statistical analysis of Zr/Rb, K/Ti and V/Cr elemental ratios suggests that the system was impacted by long-eccentricity (400 kyr) cyclicity. The δ13C excursion in organic carbon (δ13Corg) record signals a large negative carbon isotope excursion (CIE) associated with the mass extinction event, but also records a second, smaller negative CIE ca. 22 m above this interval. This younger δ13Corg excursion correlates to similar CIEs in the Dienerian (late Induan) records of other sections, notably in the Tethys Ocean, which have been interpreted as recording a small biotic crisis during the post-extinction recovery. Evidence of this negative CIE in Spitsbergen suggests that the Dienerian crisis may have been global in extent. The negative δ13Corg values are associated with evidence for dysoxia or anoxia in the core, and the occurrence of tephra layers in the same interval suggests a possible connection between the Dienerian crisis and a discrete episode of volcanic activity.

Constraints of magnetostratigraphic and mineralogical data on the provenance of sediments in the Parece Vela Basin of the western Pacific

The sediment provenance and sedimentary processes of the Parece Vela Basin in the western Pacific during the last ca. 1 Myr were studied based on the analysis of magnetic properties, mineral features, and paleomagnetic ages of core C-P19. The results show that the sedimentary sequence has a lower limit age younger than 1.072 Ma, and the sedimentation process can be divided into two stages with sedimentation rates of 4.0 mm/kyr during ca. 1–0.78 Ma and 3.6 mm/kyr since 0.78 Ma. These sedimentation rates are higher than those in the surrounding area, where the sedimentation rate is generally less than 2 mm/kyr. Taken together with the mineral features and magnetic parameters, these findings show that volcanic sediments eroded from the nearby ridge were transported by currents to the sampling site. These volcanic sediments represent the main source of sediment in the area, with eolian inputs contributing little and nonbiogenic authigenic magnetite accounting for part of the magnetic fraction. The sedimentary environment and sediment provenance have varied during the last approximately 1 million years. During 997–880 ka, volcanic activity increased, and the input of volcanic clasts was high, whereas during 880–443 ka, the sedimentary environment tended to be stable, and the sediment supply decreased. With the increase in volcanic activity in the western Pacific, the sediment input increased again during ca. 443 ka-present.

Interaction between seismicity and deformation on different time scales in volcanic areas: Campi Flegrei and Stromboli

Abstract. We study oscillations recorded at Stromboli and Campi Flegrei by different sensors: seismometers, strainmeters and tiltmeters. We examine both the high-frequency (>0.5 Hz) portion of the spectrum and very long period signals up to tidal scales. In this context, seismicity and deformation are investigated on different time scales (from minutes to days/years) in order to identify the basic elements of their interaction, whose understanding should provide new insights on the predictive models. In this work, the strict relation of tides and volcanic processes is shown. At Stromboli, indeed the transition from the stationary phase to the non-stationary phase seems to have a tidal precursor that is related to the duration of the crisis. The subsequent volcanic activity is interpreted as the response of the volcano to restore the equilibrium condition. The moveout from equilibrium produces, first, variations in the standard statistics of explosions, then leads to effusive stage and to a pressure drop in the shallow feeding system. That process induces the nucleation of a gas bubble and the excitation of low frequencies. Campi Flegrei seismicity shows a correlation between the diurnal solar solid tide and the energy released by the long period signals, indicating that the whole mechanism is modulated on a tidal scale. In other words, in the case of Stromboli, a departure from the equilibrium state is marked by solid tide variations in a certain frequency band. On the other hand, at Campi Flegrei diurnal to annual solid tides modulate an increase of volcanic activity.

DETECTING DEFORMATION DUE TO THE 2018 MERAPI VOLCANO ERUPTION USING INTERFEROMETRIC SYNTHETIC APERTURE RADAR (INSAR) FROM SENTINEL-1 TOPS

This paper describes the application of Sentinel-1 TOPS (Terrain Observation with Progressive Scans), the latest generation of SAR satellite imagery, to detect displacement of the Merapi volcano due to the May–June 2018 eruption. Deformation was detected by measuring the vertical displacement of the surface topography around the eruption centre. The Interferometric Synthetic Aperture Radar (InSAR) technique was used to measure the vertical displacement. Furthermore, several Landsat-8 Thermal Infra Red Sensor (TIRS) imageries were used to confirm that the displacement was generated by the volcanic eruption. The increasing temperature of the crater was the main parameter derived using the Landsat-8 TIRS, in order to determine the increase in volcanic activity. To understand this phenomenon, we used Landsat-8 TIRS acquisition dates before, during and after the eruption. The results show that the eruption in the May–June 2018 period led to a small negative vertical displacement. This vertical displacement occurred in the peak of volcano range from -0.260 to -0.063 m. The crater, centre of eruption and upper slope of the volcano experienced negative vertical displacement. The results of the analysis from Landsat-8 TIRS in the form of an increase in temperature during the 2018 eruption confirmed that the displacement detected by Sentinel-1 TOPS SAR was due to the impact of volcanic activity. Based on the results of this analysis, it can be seen that the integration of SAR and thermal optical data can be very useful in understanding whether deformation is certain to have been caused by volcanic activity.

Mercury anomalies across the Palaeocene–Eocene Thermal Maximum

Abstract. Large-scale magmatic events like the emplacement of the North Atlantic Igneous Province (NAIP) are often coincident with periods of extreme climate change such as the Palaeocene–Eocene Thermal Maximum (PETM). One proxy for volcanism in the geological record that is receiving increased attention is the use of mercury (Hg) anomalies. Volcanic eruptions are among the dominant natural sources of Hg to the environment; thus, elevated Hg∕TOC values in the sedimentary rock record may reflect an increase in volcanic activity at the time of deposition. Here we focus on five continental shelf sections located around the NAIP in the Palaeogene. We measured Hg concentrations, total organic carbon (TOC) contents, and δ13C values to assess how Hg deposition fluctuated across the PETM carbon isotope excursion (CIE). We find a huge variation in Hg anomalies between sites. The Grane field in the North Sea, the most proximal locality to the NAIP analysed, shows Hg concentrations up to 90 100 ppb (Hg∕TOC = 95 700 ppb wt %−1) in the early Eocene. Significant Hg∕TOC anomalies are also present in Danish (up to 324 ppb wt %−1) and Svalbard (up to 257 ppb wt %−1) sections prior to the onset of the PETM and during the recovery period, while the Svalbard section also shows a continuous Hg∕TOC anomaly during the body of the CIE. The combination with other tracers of volcanism, such as tephra layers and unradiogenic Os isotopes, at these localities suggests that the Hg∕TOC anomalies reflect pulses of magmatic activity. In contrast, we do not observe clear Hg anomalies on the New Jersey shelf (Bass River) or the Arctic Ocean (Lomonosov Ridge). This large spatial variance could be due to more regional Hg deposition. One possibility is that phreatomagmatic eruptions and hydrothermal vent complexes formed during the emplacement of sills led to submarine Hg release, which is observed to result in limited distribution in the modern era. The Hg∕TOC anomalies in strata deposited prior to the CIE may suggest that magmatism linked to the emplacement of the NAIP contributed to the initiation of the PETM. However, evidence for considerable volcanism in the form of numerous tephra layers and Hg∕TOC anomalies post-PETM indicates a complicated relationship between LIP volcanism and climate. Factors such as climate system feedbacks, changes to the NAIP emplacement style, and/or varying magma production rates may be key to both the onset and cessation of hyperthermal conditions during the PETM. However, processes such as diagenesis and organic matter sourcing can have a marked impact on Hg∕TOC ratios and need to be better constrained before the relationship between Hg anomalies and volcanic activity can be considered irrefutable.

Volcanic activities triggered or inhibited by resonance of volcanic edifices to large earthquakes

The existence of a causal link between large earthquakes and volcanic unrest is widely accepted. Recent observations have also revealed counterintuitive negative responses of volcanoes to large earthquakes, including decreased gas emissions and subsidence in volcanic areas. In order to explore the mechanisms that could simultaneously explain both the positive and negative responses of volcanic activity to earthquakes, we here focus on the role played by topography. In the laboratory, we shook a volcanic edifice analogue, made of gel, previously injected with a buoyant fluid. We find that shaking triggers rapid migration of the buoyant fluid upward, downward, or laterally, depending on the fluid’s buoyancy and storage depth; bubbly fluids stored at shallow depth ascend, while low-buoyancy fluids descend or migrate laterally. The migration of fluids induced by shaking is two orders of magnitude faster than without shaking. Downward or lateral fluid migration may decrease volcanic gas emissions and cause subsidence as a negative response, while upward migration is consistent both with an increase in volcanic activity and immediate unrest (deformation and seismicity) after large earthquakes. The fluid migration is more efficient when the oscillation frequency is close to the resonance frequency of the edifice. The resonance frequency for a 30-km-wide volcanic mountain range, such as those where subsidence was observed, is ∼0.07 Hz. Only large earthquakes are able to cause oscillation at such low frequencies.

The Influence of Io's 2015 Volcanic Activity on Jupiter's Magnetospheric Dynamics

AbstractEmbedded deep inside the huge magnetosphere of Jupiter, the moon Io has active volcanos. Jovian magnetospheric dynamics are driven by the expulsion of Iogenic plasma in the strongly magnetized, fast‐rotating system and should vary in response to Io's volcanic activity. In early 2015 when various observations indicated an increase in volcanic activity, the EXCEED instrument onboard the Hisaki spacecraft continuously observed the Jovian magnetosphere via the aurora emission and the emission from the Io plasma torus. The plasma diagnosis of the enhanced Io plasma torus spectrum along with a physical chemistry model for deducing plasma parameters revealed a higher plasma density and a 2–4 times faster radial flow as compared with a volcanically quiet period. Aurora emissions reflecting midmagnetospheric activities showed multiple highly elevated brightness peaks about a month later. Long‐term and continuous monitoring by Hisaki enabled the first comprehensive observations of the Jovian magnetosphere in response to Io's enhanced volcanic activity.

Temporal variation in source location of continuous tremors before ash\u2013gas emissions in January 2014 at Aso volcano, Japan

Volcanic tremor is often observed to be associated with an increase in volcanic activity and during periods approaching eruptions. It is therefore of crucial importance to study this phenomenon. The opening of a new vent and subsequent ash–gas emissions was observed in the active crater (Nakadake crater) of Aso volcano, Japan, in January 2014. These events were considered to be associated with phreatomagmatic activity similar to the small events of 2003–2005. During the period from December 2013 to January 2014, a significant variation in the amplitude of continuous seismic tremors was observed corresponding to surficial volcanic activity. We estimated the tremor source locations for this two-month period by a three-dimensional grid search using the tremor amplitude ratio of 5–10 Hz band-pass filtered waveforms. The estimated source locations were distributed in a roughly cylindrical region (100–150 m in diameter) ranging from the ground surface to a depth of 400 m. Migration of the estimated source location was also identified and was associated with changes in volcanic activity. We assumed that the source locations coincided with a conduit system of the volcano, consisting of networks of fractures. This area is likely situated above the crack-like conduit proposed in previous studies. Before the 2014 event, an increase in gas-dominated volcanic fluid first caused an enlargement of the conduit zone, followed by the migration of further magmatic fluid through other pathways, which resulted in a subsequent ash–gas emission. Although we do not have sufficient information to discuss the causal relationship between these processes, it seems reasonable that continuous tremors might change the conduit conditions.

Redox conditions, productivity, and volcanic input during deposition of uppermost Jurassic and Lower Cretaceous organic-rich siltstones in Spitsbergen, Norway

In this paper, uppermost Jurassic and Lower Cretaceous black organic-rich siltstones (Rurikfjellet Formation) from Carolinedalen (Isfjorden, Spitsbergen) are studied using integrated palynological, petrographic, and geochemical methods (organic and inorganic geochemistry as well as Rock-Eval pyrolysis) in order to decipher the depositional conditions prevailing during their sedimentation, the type of organic matter from which they were formed, and their potential for generating hydrocarbons. The age of these investigated sediments encompasses an interval from the upper Tithonian-Berriasian to the Hauterivian, dated on the basis of dinocyst biostratigraphy. The ammonoids found in loose form at the base of the investigated section, such as Laugeites groenlandicus, are indicative of the upper part of the middle Tithonian. Based on palynology, biomarkers, and Rock-Eval data, the kerogen in the investigated siltstones from Isfjorden is of the mixed II/III type; the organic matter is mixed marine and terrestrial in origin, and represents the early to peak ‘oil window’ maturation stage (Tmax around 440 °C).These siltstones were deposited under a high-productivity regime with oxic/dysoxic bottom water conditions, as evidenced from the size distribution of pyrite framboids, in which pyrites with diameters >5 μm predominate. Values of Th/U and Corg/P ratios generally above 3 and 30, respectively, along with pristane/phytane ratios >2 and sterane/hopane ratios <0.3, also indicate oxic to suboxic sedimentary conditions in the water column. Anoxia, if present, must have been short-lasting and formed oxygen minimum zone in the water column. Elevated productivity in the photic zone may have been generated by an increase in volcanic activity, as confirmed by higher Hg contents and/or terrigenous nutrient supply.

Late Neolithic to Middle Bronze Age (around 4900–3100 cal. BP) lake-level fluctuations at Lake Neuchâtel (Switzerland) as reflected by the sediment sequence of the site of Colombier/Les Plantées de Rive: Palaeoclimatic and archaeological implications

Recent archaeological investigations at the site of Colombier/Les Plantées de Rive (COL-PR) on the northwestern shore of Lake Neuchâtel (Switzerland) revealed an exceptional concentration of anthropic structures from the Late Neolithic to the Late Bronze Age interbedded within an alternation of terrestrial and lacustrine deposits. The chronology is based on radiocarbon dates from terrestrial material and on artefacts found in archaeological structures. Using various proxies, the sedimentological analysis of the COL-PR sediment sequence allows the reconstruction of lake-level fluctuations for the period 4900–3300 cal. BP. Three major lake-level highstands occurring at ca. 4900 (Late Neolithic), 3650 (Early Bronze Age) and 3400 cal. BP (Middle Bronze Age) have been related to the possible influences of decreases in the solar activity sometimes accentuated by increases in volcanic activity. The COL-PR site provides robust data to document the climatic deterioration assumed to be responsible for the abandonment of the lake-dwellings north of the Alps during the Middle and the early Late Bronze Age. In addition, the interbedding of successive monuments within terrestrial as well as lacustrine deposits suggests a significant role played over hundred years by the collective memory in the perpetuation of the ceremonial and funeral vocation of the site and its spatial organisation at the interface between lacustrine and terrestrial domains, despite interruptions provoked by major lake-level rises associated with worsening of climatic conditions.

Quantifying the impact of early 21st century volcanic eruptions on global-mean surface temperature

Despite a continuous increase in well-mixed greenhouse gases, the global-mean surface temperature has shown a quasi-stabilization since 1998. This muted warming has been linked to the combined effects of internal climate variability and external forcing. The latter includes the impact of recent increase in the volcanic activity and of solar irradiance changes. Here we used a high-resolution coupled ocean–atmosphere climate model to assess the impact of the recent volcanic eruptions on the Earth's temperature, compared with the low volcanic activity of the early 2000s. Two sets of simulations are performed, one with realistic aerosol optical depth values, and the other with a fixed value of aerosol optical depth corresponding to a period of weak volcanic activity (1998–2002). We conclude that the observed recent increase in the volcanic activity led to a reduced warming trend (from 2003 to 2012) of 0.08 °C in ten years. The induced cooling is stronger during the last five-year period (2008–2012), with an annual global mean cooling of 0.04 °C (+/− 0.04 °C). The cooling is similar in summer (0.05 °C +/− 0.04 °C cooling) than in winter (0.03 °C +/− 0.04 °C cooling), but stronger in the Northern Hemisphere than in the Southern Hemisphere. Although equatorial and Arctic precipitation decreases in summer, the change in precipitation does not indicate robust changes at a local scale. Global heat content variations are found not to be impacted by the recent increase in volcanic activity.

Interaction between climate, volcanism, and isostatic rebound in Southeast Alaska during the last deglaciation

Observations of enhanced volcanic frequency during the last deglaciation have led to the hypothesis that ice unloading in glaciated volcanic terrains can promote volcanism through decompression melting in the shallow mantle or a reduction in crustal magma storage time. However, a direct link between regional climate change, isostatic adjustment, and the initiation of volcanism remains to be demonstrated due to the difficulty of obtaining high-resolution well-dated records that capture short-term climate and volcanic variability traced to a particular source region. Here we present an exceptionally resolved record of 19 tephra layers paired with foraminiferal oxygen isotopes and alkenone paleotemperatures from marine sediment cores along the Southeast Alaska margin spanning the last deglacial transition. Major element compositions of the tephras indicate a predominant source from the nearby Mt. Edgecumbe Volcanic Field (MEVF). We constrain the timing of this regional eruptive sequence to 14.6–13.1 ka. The sudden increase in volcanic activity from the MEVF coincides with the onset of Bølling–Allerød interstadial warmth, the disappearance of ice-rafted detritus, and rapid vertical land motion associated with modeled regional isostatic rebound in response to glacier retreat. These data support the hypothesis that regional deglaciation can rapidly trigger volcanic activity. Rapid sea surface temperature fluctuations and an increase in local salinity (i.e., δ18Osw) variability are associated with the interval of intense volcanic activity, consistent with a two-way interaction between climate and volcanism in which rapid volcanic response to ice unloading may in turn enhance short-term melting of the glaciers, plausibly via albedo effects on glacier ablation zones.