Supereruption Research Articles

Volcanic synchronisation between the EPICA Dome C and Vostok ice cores (Antarctica) 0–145 kyr BP

Abstract. This study aims at refining the synchronisation between the EPICA Dome C (EDC) and Vostok ice cores in the time interval 0–145 kyr BP by using the volcanic signatures. 102 common volcanic events were identified by using continuous electrical conductivity (ECM), di-electrical profiling (DEP) and sulfate measurements while trying to minimize the distortion of the glaciological chronologies. This is an update and a continuation of previous works performed over the 0–45 kyr interval that provided 56 tie points to the ice core chronologies (Udisti et al., 2004). This synchronisation will serve to establish Antarctic Ice Core Chronology 2012, the next synchronised Antarctic dating. A change of slope in the EDC-depth/Vostok-depth diagram is probably related to a change of accumulation regime as well as to a change of ice thickness upstream of the Lake Vostok, but we did not invoke any significant temporal change of surface accumulation at EDC relative to Vostok. No significant phase difference is detected between the EDC and Vostok isotopic records, but depth shifts between the Vostok 3G and 5G ice cores prevent from looking at this problem accurately. Three possible candidates for the Toba volcanic super-eruption ~73 kyr ago are suggested in the Vostok and EDC volcanic records. Neither the ECM, DEP nor the sulfate fingerprints for these 3 events are significantly larger than many others in the records.

Super Eruption and “Volcanic Winter”

Super Eruption and “Volcanic Winter”

The influence of eruption season on the global aerosol evolution and radiative impact of tropical volcanic eruptions

Abstract. Simulations of tropical volcanic eruptions using a general circulation model with coupled aerosol microphysics are used to assess the influence of season of eruption on the aerosol evolution and radiative impacts at the Earth's surface. This analysis is presented for eruptions with SO2 injection magnitudes of 17 and 700 Tg, the former consistent with estimates of the 1991 Mt. Pinatubo eruption, the later a near-"super eruption". For each eruption magnitude, simulations are performed with eruptions at 15° N, at four equally spaced times of year. Sensitivity to eruption season of aerosol optical depth (AOD), clear-sky and all-sky shortwave (SW) radiative flux is quantified by first integrating each field for four years after the eruption, then calculating for each cumulative field the absolute or percent difference between the maximum and minimum response from the four eruption seasons. Eruption season has a significant influence on AOD and clear-sky SW radiative flux anomalies for both eruption magnitudes. The sensitivity to eruption season for both fields is generally weak in the tropics, but increases in the mid- and high latitudes, reaching maximum values of ~75 %. Global mean AOD and clear-sky SW anomalies show sensitivity to eruption season on the order of 15–20 %, which results from differences in aerosol effective radius for the different eruption seasons. Smallest aerosol size and largest cumulative impact result from a January eruption for Pinatubo-magnitude eruption, and from a July eruption for the near-super eruption. In contrast to AOD and clear-sky SW anomalies, all-sky SW anomalies are found to be insensitive to season of eruption for the Pinatubo-magnitude eruption experiment, due to the reflection of solar radiation by clouds in the mid- to high latitudes. However, differences in all-sky SW anomalies between eruptions in different seasons are significant for the larger eruption magnitude, and the ~15 % sensitivity to eruption season of the global mean all-sky SW anomalies is comparable to the sensitivity of global mean AOD and clear-sky SW anomalies. Our estimates of sensitivity to eruption season are larger than previously reported estimates: implications regarding volcanic AOD timeseries reconstructions and their use in climate models are discussed.

The Expansion of mtDNA Haplogroup L3 within and out of Africa

Although fossil remains show that anatomically modern humans dispersed out of Africa into the Near East ∼100 to 130 ka, genetic evidence from extant populations has suggested that non-Africans descend primarily from a single successful later migration. Within the human mitochondrial DNA (mtDNA) tree, haplogroup L3 encompasses not only many sub-Saharan Africans but also all ancient non-African lineages, and its age therefore provides an upper bound for the dispersal out of Africa. An analysis of 369 complete African L3 sequences places this maximum at ∼70 ka, virtually ruling out a successful exit before 74 ka, the date of the Toba volcanic supereruption in Sumatra. The similarity of the age of L3 to its two non-African daughter haplogroups, M and N, suggests that the same process was likely responsible for both the L3 expansion in Eastern Africa and the dispersal of a small group of modern humans out of Africa to settle the rest of the world. The timing of the expansion of L3 suggests a link to improved climatic conditions after ∼70 ka in Eastern and Central Africa rather than to symbolically mediated behavior, which evidently arose considerably earlier. The L3 mtDNA pool within Africa suggests a migration from Eastern Africa to Central Africa ∼60 to 35 ka and major migrations in the immediate postglacial again linked to climate. The largest population size increase seen in the L3 data is 3-4 ka in Central Africa, corresponding to Bantu expansions, leading diverse L3 lineages to spread into Eastern and Southern Africa in the last 3-2 ka.

The Ammonia Tanks Tuff: Erupting a melt-rich rhyolite cap and its remobilized crystal cumulate

Super-volcanic eruption deposits, such as the Ammonia Tanks Tuff (AT; ~ 900 km 3), typically record the explosive evacuation of a chemically and thermally zoned shallow magma reservoir. Such zoning patterns require either 1) mixing between two magmas or 2) in-situ differentiation driven by crystal–liquid separation. Here we show, using a geochemical model firmly grounded on natural observations, that these processes are not mutually exclusive. Using an initial trachydacitic magma, the interstitial liquid evolves to a rhyolitic composition as the magma reaches high crystallinity (mush state; ≥~50% crystals). The low-density rhyolitic melt then migrates upwards and leaves behind a trachyandesite cumulate with distinctive trace element concentrations (e.g., high Ba, Sr, Zr) that can be modeled by crystal fractionation. During eruption, both liquid cap and underlying cumulate are evacuated from a shallow reservoir, leading to the observed chemical gradient. However, to account for the thermal gradient and low crystal fraction (~ 25 vol.%) in the cumulate trachyandesite of the AT tuff, a mixing stage with hot mafic recharge must have occurred prior to eruption. The late recharge induced heating, partially melting a significant portion of the crystal cargo and ultimately triggering the eruption.

Local- and regional-scale impacts of the ∼74 ka Toba supervolcanic eruption on hominin populations and habitats in India

The Toba supervolcanic eruption of ∼74,000 years ago is argued to have devastated Homo sapiens populations, causing a human population bottleneck. Through a combination of rapid global climatic deterioration and ecological disruption following the widespread ash-fall, this dramatic eruption, the largest in at least the last 2 million years, is hypothesized to have shaped the genetic structure and diversity of human populations today. Past assessments of Toba’s human impacts, however, have been predominantly theoretical. Using archaeological and geological evidence from sites in India, this study addresses Toba’s local-scale impacts on hominin technology, behavior, demography and habitats in two valleys in India (the Jurreru and Middle Son valleys). Using paleoclimatological and volcanological data, regional-scale impacts throughout India are inferred. A refugia hypothesis is presented that argues for variation in the scale of Toba’s impact throughout India, driven by regional differences in monsoonal dynamics, geography and topography. Areas of north-west India, the Indo-Gangetic Plain and parts of the Deccan to the east of the Western Ghats are argued to have been the most affected, whereas areas of southern and eastern India may have preserved the largest refugia for hominin populations.

A southern Indian Middle Palaeolithic occupation surface sealed by the 74 ka Toba eruption: Further evidence from Jwalapuram Locality 22

This paper reports further evidence from an archaeological occupation surface in southern India that was buried by tephra from the Toba volcanic super-eruption ca. 74,000 years ago. The open-air site, designated Jwalapuram Locality 22 and located in the Kurnool District of Andhra Pradesh, preserves more than 1600 stone artefacts assigned to the Indian Middle Palaeolithic. Sedimentological, isotopic and lithic data along with optically stimulated luminescence ages confirm the site as occupied closely prior to the eruption. The hominin taxon responsible for creating the site is not known, but the stone tool evidence is most consistent with contemporaneous Homo sapiens technologies in Africa and to the east of South Asia. The findings have relevance for understanding Indian Middle Palaeolithic technology, and for identifying the behavioural and environmental adaptations of the hominin group(s) that occupied India when Toba erupted.

The Toba volcanic super-eruption, environmental change, and hominin occupation history in India over the last 140,000 years

A prolonged, interdisciplinary fieldwork program was initiated in India to investigate the impact of the Toba super-eruption on terrestrial ecosystems and hominins. Fieldwork was centered on the Jurreru River Valley and the Middle Son River Valley, in southern and northern India. Archaeological sites span from 140,000 years ago through to the Holocene, providing a long-term view about hominin occupation history. Primary air-fall deposits of the Young Toba Tuff (YTT) were identified and changes in terrestrial environments prior to and after the super-eruption are indicated. Prior to the Toba eruption, drying of local ecological settings was underway. The emplacement of ash on landscapes and its subsequent erosion had local ecological and hydrological effects. Although drier conditions are indicated after the deposition of the ash deposits, a mosaic of environments was present in India, indicating that animals and hominins could have survived the volcanic event. Evidence indicates that Middle Paleolithic industries in stratified contexts are present in India prior to and after the Toba super-eruption. Middle Paleolithic hominins appear to have survived the negative effects of the volcanic eruption and climatic fluctuations in the Late Pleistocene. Middle Paleolithic industries, produced from ca. 77–38,000 years ago in India, were probably manufactured by Homo sapiens.

A simple relationship between volcanic sulfate aerosol optical depth and surface temperature change simulated in an atmosphere-ocean general circulation model

[1] In this study we quantify the relationship between the aerosol optical depth increase from a volcanic eruption and the severity of the subsequent surface temperature decrease. This investigation is made by simulating 10 different sizes of eruption in a global circulation model (GCM) by changing stratospheric sulfate aerosol optical depth at each time step. The sizes of the simulated eruptions range from Pinatubo-sized up to the magnitude of supervolcanic eruptions around 100 times the size of Pinatubo. From these simulations we find that there is a smooth monotonic relationship between the global mean maximum aerosol optical depth anomaly and the global mean temperature anomaly and we derive a simple mathematical expression which fits this relationship well. We also construct similar relationships between global mean aerosol optical depth and the temperature anomaly at every individual model grid box to produce global maps of best-fit coefficients and fit residuals. These maps are used with caution to find the eruption size at which a local temperature anomaly is clearly distinct from the local natural variability and to approximate the temperature anomalies which the model may simulate following a Tambora-sized eruption. To our knowledge, this is the first study which quantifies the relationship between aerosol optical depth and resulting temperature anomalies in a simple way, using the wealth of data that is available from GCM simulations.

Research Spotlight: New evidence could let supereruption off the hook

It's a case of forensic analysis on the grandest scale: the possible near‐extinction of the entire human race at the hands of one volcanic supereruption. The Younger Toba Tuff (YTT) eruption 74,000 years ago has been accused of blanketing the sky with sulfate aerosols and driving the world into a long‐lasting winter. In a new study,Timmreck et al. have given the Sumatran volcano a climatological alibi. The authors used a global circulation model to simulate the YTT eruption, including for the first time an analysis of the small‐scale interactions between sulfate particles. Sulfate particles in the upper atmosphere strongly reflect incoming solar radiation, which has a cooling effect on the Earth. (Geophysical Research Letters, doi:10.1029/2010GL045464, 2010)

Erratum to: Zircon-scale insights into the history of a Supervolcano, Bishop Tuff, Long Valley, California, with implications for the Ti-in-zircon geothermometer

Erratum to: Zircon-scale insights into the history of a Supervolcano, Bishop Tuff, Long Valley, California, with implications for the Ti-in-zircon geothermometer

Volcanism and associated hazards: the Andean perspective

Abstract. Andean volcanism occurs within the Andean Volcanic Arc (AVA), which is the product of subduction of the Nazca Plate and Antarctica Plates beneath the South America Plate. The AVA is Earth's longest but discontinuous continental-margin volcanic arc, which consists of four distinct segments: Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone, and Austral Volcanic Zone. These segments are separated by volcanically inactive gaps that are inferred to indicate regions where the dips of the subducting plates are too shallow to favor the magma generation needed to sustain volcanism. The Andes host more volcanoes that have been active during the Holocene (past 10 000 years) than any other volcanic region in the world, as well as giant caldera systems that have produced 6 of the 47 largest explosive eruptions (so-called "super eruptions") recognized worldwide that have occurred from the Ordovician to the Pleistocene. The Andean region's most powerful historical explosive eruption occurred in 1600 at Huaynaputina Volcano (Peru). The impacts of this event, whose eruptive volume exceeded 11 km3, were widespread, with distal ashfall reported at distances >1000 km away. Despite the huge size of the Huaynaputina eruption, human fatalities from hazardous processes (pyroclastic flows, ashfalls, volcanogenic earthquakes, and lahars) were comparatively small owing to the low population density at the time. In contrast, lahars generated by a much smaller eruption (<0.05 km3) in 1985 of Nevado del Ruiz (Colombia) killed about 25 000 people – the worst volcanic disaster in the Andean region as well as the second worst in the world in the 20th century. The Ruiz tragedy has been attributed largely to ineffective communications of hazards information and indecisiveness by government officials, rather than any major deficiencies in scientific data. Ruiz's disastrous outcome, however, together with responses to subsequent hazardous eruptions in Chile, Colombia, Ecuador, and Peru has spurred significant improvements in reducing volcano risk in the Andean region. But much remains to be done.

India at the cross-roads of human evolution

The Indian palaeoanthropological record, although patchy at the moment, is improving rapidly with every new find. This broad review attempts to provide an account of (a) the Late Miocene fossil apes and their gradual disappearance due to ecological shift from forest dominated to grassland dominated ecosystem around 9-8 Ma ago, (b) the Pliocene immigration/evolution of possible hominids and associated fauna, (c) the Pleistocene record of fossil hominins, associated fauna and artifacts, and (d) the Holocene time of permanent settlements and the genetic data from various human cultural groups within India. Around 13 Ma ago (late Middle Miocene) Siwalik forests saw the emergence of an orangutan-like primate Sivapithecus. By 8 Ma, this genus disappeared from the Siwalik region as its habitat started shrinking due to increased aridity influenced by global cooling and monsoon intensification. A contemporary and a close relative of Sivapithecus, Gigantopithecus (Indopithecus), the largest ape that ever-lived, made its first appearance at around 9 Ma. Other smaller primates that were pene-contemporaneous with these apes were Pliopithecus (Dendropithecus), Indraloris, Sivaladapis and Palaeotupia. The Late Pliocene and Early Pleistocene witnessed northern hemisphere glaciations, followed by the spread of arid conditions on a global scale, setting the stage for hominids to explore "Savanahastan". With the prominent expansion of grassland environments from East Africa to China and Indonesia in the Pliocene, monkeys and baboons dispersed into the Indian subcontinent from Africa along with other mammals. Though debated, there are several claims of the presence of early hominins in this part of the world during the Late Pliocene, based primarily on the recovery of Palaeolithic tools. Fossils of our own ancestor and one of the first globe-trotters, early Homo erectus, has been documented from the Early Pleistocene of East Africa, Western Asia and Southeast Asia, thus indirectly pointing towards Indian subcontinent as a possible migration corridor between these regions. The only definite pre-Homo sapiens fossil hominin remains come from the Central Narmada Valley and are thought to be of Middle to late Pleistocene age, and the cranium has been shown to be closely linked to archaic Homo sapiens/H. heidelbergensis of Europe. Around approximately 74,000 yrs ago, a super volcanic eruption in Sumatra caused the deposition of Youngest Toba Tephra, that covered large parts of the Indian peninsula. Just around this time anatomically-and-behaviorally modern humans or Homo sapiens possibly arrived into India as evidenced by the so called Middle and Upper Palaeolithic assemblages and associated symbolic evidence. The available genetic data reveals that the gene pool to which modern Indians races belong was extremely diverse and had variable mixed links with both European and Asian populations.

Did the Toba volcanic eruption of ∼74 ka B.P. produce widespread glaciation?

It has been suggested that the Toba volcanic eruption, approximately 74 ka B.P., was responsible for the extended cooling period and ice sheet advance immediately following it, but previous climate model simulations, using 100 times the amount of aerosols produced by the 1991 Mount Pinatubo eruption, have been unable to produce such a prolonged climate response. Here we conduct six additional climate model simulations with two different climate models, the National Center for Atmospheric Research Community Climate System Model 3.0 (CCSM3.0) and National Aeronautics and Space Administration Goddard Institute for Space Studies ModelE, in two different versions, to investigate additional mechanisms that may have enhanced and extended the forcing and response from such a large supervolcanic eruption. With CCSM3.0 we include a dynamic vegetation model to explicitly calculate the feedback of vegetation death on surface fluxes in response to the large initial reduction in transmitted light, precipitation, and temperature. With ModelE we explicitly calculate the effects of an eruption on stratospheric water vapor and model stratospheric chemistry feedbacks that might delay the conversion of SO2 into sulfate aerosols and prolong the lifetime and radiative forcing of the stratospheric aerosol cloud. To span the uncertainty in the amount of stratospheric injection of SO2, with CCSM3.0 we used 100 times the Pinatubo injection, and with ModelE we used 33, 100, 300, and 900 times the Pinatubo injection without interactive chemistry, and 300 times Pinatubo with interactive chemistry. Starting from a roughly present‐day seasonal cycle of insolation, CO2 concentration, and vegetation, or with 6 ka B.P. conditions for CCSM3.0, none of the runs initiates glaciation. The CCSM3.0 run produced a maximum global cooling of 10 K and ModelE runs produced 8–17 K of cooling within the first years of the simulation, depending on the injection, but in all cases, the climate recovers over a few decades. Nevertheless, the “volcanic winter” following a supervolcano eruption of the size of Toba today would have devastating consequences for humanity and global ecosystems. These simulations support the theory that the Toba eruption indeed may have contributed to a genetic bottleneck.

Mass-independent isotopic signatures of volcanic sulfate from three supereruption ash deposits in Lake Tecopa, California

Hundreds to thousands of megatons of sulfur dioxide released by supereruptions can change chemical and physical properties of the atmosphere and thus induce climate perturbations. We present oxygen and sulfur isotope analyses of sulfate in 48 volcanic ash samples, and 26 sediment samples from dry lake beds in the Tecopa basin, California, USA. These ash layers represent three supereruptions, including the 0.64 Ma Lava Creek Tuff, 2.04 Ma Huckleberry Ridge Tuff and 0.76 Ma Bishop Tuff. Mass-independent oxygen signatures (Δ 17O up to 2.26‰) that are present in these ash units, and not in associated sediments, indicate oxidation of volcanic SO 2 by mass-independent ozone and its products. In this study, we consider the formation, deposition, preservation and dilution of mass-independent volcanic sulfate (MIVS). Using the isotopic compositions of the sulfates, we construct a mixing model that demonstrates that the main source of sulfate in Lake Tecopa is mass-dependent sediment-derived sulfate (MDSDS, > 77%). However, ash beds still preserve up to 23% of MIVS that initially had undiluted Δ 17O value around 8‰, and Δ 33S as low as − 0.35‰, and Δ 36S up to 1.08‰. Therefore, despite potential dilution by MDSDS, the MIVS signatures can be preserved in the geologic record for few million years, if deposited as gypsum in arid environments, alkaline or saline lake. The oxygen and sulfur mass-independent signatures of the volcanic sulfates indicate that photolysis and oxidation of volcanic SO 2 has been achieved in the upper atmosphere. Since only supervolcanic eruptions were shown to generate massive amount of mass-independent sulfate, it requires that up to 20–60% of the global ozone layer is consumed as a result of supervolcanic SO 2 released. This may occur as a result of a strong physical and chemical degradation of the tropopause; we speculate that the distinction between the high-troposphere and the low-stratosphere, at least locally, could be erased by supereruptions, and recorded by MIVS.

P,Svelocity andVP/VSratio beneath the Toba caldera complex (Northern Sumatra) from local earthquake tomography

In this paper, we investigate the crustal and uppermost mantle structure beneath Toba caldera, which is known as the location of one of the largest Cenozoic eruptions on Earth. The most recent event occurred 74 000 yr BP, and had a significant global impact on climate and the biosphere. In this study, we revise data on local seismicity in the Toba area recorded by a temporary PASSCAL network in 1995. We applied the newest version of the LOTOS-07 algorithm, which includes absolute source location, optimization of the starting 1-D velocity model, and iterative tomographic inversion for 3-D seismic P, S (or the VP/VS ratio) and source parameters. Special attention is paid to verification of the obtained results. Beneath the Toba caldera and other volcanoes of the arc, we observe relatively moderate (for volcanic areas) negative P- and S-velocity anomalies that reach 18 per cent in the uppermost layer, 10–12 per cent in the lower crust and about 7 per cent in the uppermost mantle. Much stronger contrasts are observed for the VP/VS ratio that is a possible indicator of dominant effect of melting in origin of seismic anomalies. At a depth of 5 km beneath active volcanoes, we observe small patterns (7–15 km size) with a high VP/VS ratio that might be an image of actual magmatic chambers filled with partially molten material feeding the volcanoes. In the mantle wedge, we observe a vertical anomaly with low P and S velocities and a high VP/VS ratio that link the cluster of events at 120–140 km depth with Toba caldera. This may be an image of ascending fluids and melts released from the subducted slab due to phase transitions. However, taking into account poor vertical resolution, these results should be interpreted with prudence. Although the results show clear signatures that are quite typical for volcanic areas (low velocity and high VP/VS ratio beneath volcanoes), we do not observe any specific features in seismic structure that could characterize Toba as a super volcano.

The Campanian Ignimbrite (southern Italy) geochemical zoning: insight on the generation of a super-eruption from catastrophic differentiation and fast withdrawal

More than ca 100 km3 of nearly homogeneous crystal-poor phonolite and ca 100 km3 of slightly zoned trachyte were erupted 39 ka during the Campanian Ignimbrite super eruption, the most powerful in the Neapolitan area. Partition coefficient calculations, equilibrium mineral assemblages, glass compositions and texture were used to reconstruct compositional, thermal and pressure gradients in the pre-eruptive reservoir as well as timing and mechanisms of evolution towards magma chamber overpressure and eruption. Our petrologic data indicate that a wide sill-like trachytic magma chamber was active under the Campanian Plain at 2.5 kbar before CI eruption. Thermal exchange between high liquidus (1199°C) trachytic sill and cool country rocks caused intense undercooling, driving a catastrophic and fast (102 years) in situ fractional crystallization and crustal assimilation that produced a water oversaturated phonolitic cap and an overpressure in the chamber that triggered the super eruption. This process culminated in an abrupt reservoir opening and in a fast single-step high decompression. Sanidine phenocrysts crystal size distributions reveal high differentiation rate, thus suggesting that such a sill-like magmatic system is capable of evolving in a very short time and erupting suddenly with only short-term warning.

Super-eruption: no problem?

Super-eruption: no problem?

New Zealand Andesites: Priming the lithosphere for a supervolcano

New Zealand Andesites: Priming the lithosphere for a supervolcano

Extreme natural hazards: population growth, globalization and environmental change

Mankind is becoming ever more susceptible to natural disasters, largely as a consequence of population growth and globalization. It is likely that in the future, we will experience several disasters per year that kill more than 10,000 people. A calamity with a million casualties is just a matter of time. This situation is mainly a consequence of increased vulnerability. Climate change may also be affecting the frequency of extreme weather events as well as the vulnerability of coastal areas due to sea-level rise. Disastrous outcomes can only increase unless better ways are found to mitigate the effects through improved forecasting and warning, together with more community preparedness and resilience. There are particular difficulties with extreme events, which can affect several countries, while the largest events can have global consequences. The hazards of supervolcanic eruptions and asteroid impacts could cause global disaster with threats to civilization and deaths of billions of people. Although these are very rare events, they will happen and require consideration. More frequent and smaller events in the wrong place at the wrong time could have very large human, environmental and economic effects. A sustained effort is needed to identify places at risk and take steps to apply science before the events occur.