INTRODUCTIONThe geological record contains evidence of rare, explosivesupereruptions that have covered whole continents withvolcanic ash and have global long-term recurrence intervalsestimated to be in the range of 100,000–200,000 years.Supereruptions have been defined as eruptions yielding inexcess of 1 × 1015 kg of magma (>450 km3; Sparks et al. 2005).Extremely rare examples have produced vast amounts ofmagma (>1 × 1016 kg, or 4500 km3). Supereruptions lead tocaldera collapse, the formation of huge sheets of pyroclasticflow deposits (ignimbrites), as well as very extensive ash-falllayers and injection of noxious gases into the atmosphere.The effects of a future supereruption will therefore be moreviolent and damaging than those of the considerably smallereruptions that society has experienced in historic times.

The immediate effects of a supereruption will be almostunimaginably severe. Yet sooner or later, another one willoccur, and future societies must be aware of, and preparedfor, the consequences. Unlike other extreme natural hazards,there may be some degree of warning of an impendingsupereruption (Lowenstern and Hurwitz 2008 this issue).Furthermore, supereruptions are potentially long-lasting(continuing at least for many days, and in some cases inter-mittently for weeks to perhaps years; Wilson 2008 thisissue), compared to a brief but intense major earthquake ortsunami. The volcanic ash and gases released high into theatmosphere could have severe worldwide effects on climateand weather. Thus, huge explosive eruptions are one of the

few natural phenomena that canproduce truly global catastrophiceffects. They also differ from otherhazards (except meteorite impacts)in producing persistent atmosphericeffects for several years after theeruption (Rampino 2002).

This article presents an assessmentof the effects of very large explosiveeruptions, which could have con-sequences well beyond those asso-ciated with historic volcanic activity.We begin with brief descriptions ofthe eruption style and the depositsthat are produced, the gases that arereleased, and how we study them.We then turn to the duration,recurrence, and effects of supererup-tions, including their atmosphericimpact, and consider their poten-tial influence on global tempera-

ture and weather. Finally, we discuss issues facing societyafter a supereruption, including potential socio-economicimpacts. Predicting all of the effects of supereruptions isproblematic because many are outside modern experience.

PRODUCTS AND STYLES OF SUPERERUPTIONSWe have chosen here to assess the effects of a supereruptionin the range of 2000–3000 km3 of magma [4–7 × 1015 kg, orMagnitude 8.6–8.8 (Pyle 2000; see Miller and Wark 2008 thisissue), equivalent to 5000–8000 km3 of volcanic ashdeposits], an eruption like the largest from the Toba(Indonesia) or Yellowstone (USA) supervolcanoes. Allsupereruptions are associated with the formation of acaldera, a large collapse depression caused by the inwardcollapse of the crust above the magma chamber as themagma is evacuated. In the case of Toba, the present lake-filled caldera, formed incrementally by three supererup-tions, measures 100 km × 40 km and covers ~3000 km2

(Figure 2 of Miller and Wark 2008).

Solid ProductsExplosive supereruptions produce extensive ignimbrite andash-fall deposits (Wilson 2008). The great size of the ~2800 km3

Toba eruption, which took place 74,000 years ago (Rose andChesner 1987), was established after deep-sea core studiescorrelated the widespread deposits across the Indian Oceanand South China Sea (FIG. 1). Ash fall is produced by highash- and gas-laden atmospheric eruption columns that pen-etrate through the troposphere and into the stratosphere.The tropopause, separating the troposphere from the strat-osphere, is at a height of 17 km over the equator and <10 kmat 65° North or South, and it is reached by eruption columnsfrom all very large explosive eruptions.

E L E M E N T S , V O L . 4 , P P . 4 1 – 4 6 FEBRUARY 2008

Stephen Self* and Stephen Blake*

* Volcano Dynamics GroupDepartment of Earth and Environmental SciencesThe Open University, Walton HallMilton Keynes, MK7 6AA, UKE-mail: stephen.self@open.ac.uk; s.blake@open.ac.uk

Consequences of ExplosiveSupereruptions

41

Rare but extremely large explosive supereruptions lead to the catastrophicformation of huge calderas, devastation of substantial regions bypyroclastic flow deposits, and ash falls that cover continent-sized areas.

The effects of future supereruptions will be felt globally or at least by a wholehemisphere. The most widespread effects are likely to derive from the volcanicgases released, particularly sulfur gases that are converted into sulfuric acidaerosols in the stratosphere. These will remain for several years, promotingchanges in atmospheric circulation and causing surface temperatures to falldramatically in many regions, bringing about temporary reductions in lightlevels and producing severe and unseasonable weather (‘volcanic winter’).Major disruptions to global societal infrastructure can be expected forperiods of months to years, and the cost to global financial markets will behigh and sustained.

KEYWORDS: supereruptions, ash falls, pyroclastic flow deposits,

sulfate aerosols, volcanic winter

DOI: 10.2113/GSELEMENTS.4.1.41

The most destructive eruptive phenomena in supereruptionsare pyroclastic flows. These flows emanate from collapsingeruptive columns above volcanic vents. They are extremelyhot (hundreds of degrees Celsius), rapidly moving mixturesof ash and gas that hug the ground and flow for many tensof kilometres, or in extreme cases for as much as 200 km,laying down ignimbrite deposits (FIG. 2). Major pyroclasticflows such as those that formed Toba’s ignimbrite depositcan cover up to 20,000 km2 around the source volcano andbury the landscape with a layer of ash and pumice fragmentsup to 200 m thick. During emplacement they obliterateeverything in their path. The flows typically become partlybuoyant during transport, crossing topographic barriers up tohundreds of metres high and feeding fine ash into vigorouslyconvecting co-ignimbrite plumes (FIG. 2B).

The ash from these columns is dispersed by giant ash cloudsenergetic enough to spread in all directions irrespective ofstratospheric winds (Baines and Sparks 2005). This accountsfor the extremely wide dispersal of ash-fall deposits, such asthose from Yellowstone and Toba; in the latter case, theycovered an area in excess of 20 million km2, or 4% ofEarth’s surface area. With the addition of possible pumice-fall deposits from Plinian eruption columns, supereruptionash-fall deposits may be >10 m thick near their source, butthey thin down to a few centimetres or less at distances ofhundreds to thousands of kilometres downwind. Ash fromthe supereruptions at Yellowstone is known to have coveredmuch of North America, while ash from Toba is found over3000 km from its source, in northern India and offshorePakistan. Giant ash clouds are also responsible for injectingvolcanic gases high into the atmosphere.

Gaseous ProductsThe large eruption rates and extreme explosiveness ofsupereruptions are driven by the high volatile (gas) contentof the magma. The gases are released as the magma risesfrom the crustal magma chamber to the surface, in the samemanner as gas is released when a bottle of carbonated bev-erage is opened (see Zhang and Xu 2008 this issue). Themost abundant gaseous constituents are water (ca. 5% ormore of the magma by mass) and carbon dioxide (up to 0.1%),but eruptive emissions of these gases will make little differ-ence to the high concentrations already in the atmosphere.Much moist tropospheric air is also taken up in the eruption

columns and transferred to the relatively dry stratosphere.More importantly, sulfur and halogens (Cl, F and perhapsBr) released from the magma cause significant changes tothe normal atmospheric concentrations of these gases or oftheir acids H2SO4, HCl and HF (see review by Robock 2000).This is especially so in the stratosphere, where such speciesnormally occur in extremely low abundance. The sulfurcontent is particularly important because it determines theamount of sulfuric acid aerosols that subsequently form inthe stratosphere, increasing the atmospheric opacity andhence having a strong effect on climate.

The pre-eruptive (non-degassed) concentrations of S (andother volatile constituents) in magmatic liquid can be esti-mated by analyzing tiny (100 µm) inclusions of glass(quenched magmatic liquid) found in crystals that grewwithin the magma chamber, trapping the liquid and sealingit before it could degas. However, studies of glass inclusionsfrom recent explosive eruptions such as El Chichón (1982)and Pinatubo (1991) have found that the S contents deter-mined this way are insufficient, by 1 to 2 orders of magni-tude, to supply the large amounts of SO2 (7 and 20 × 109 kgSO2, respectively) that Total Ozone Mapping Spectrometer(TOMS) satellites detected in the stratosphere after theseeruptions (Bluth et al. 1997). The abundant ‘excess sulfur’ isaccounted for by the presence of a S-rich gas phase in thepre-eruptive magma. To estimate the amount of S releasedfrom a supereruption such as Toba requires a way of esti-mating the amount of gas that harbours the excess sulfurand the concentration of S in this gas.

There are two ways in which the S yield of supereruptionscan be estimated. The first is to consider supereruptions(none of which has ever been witnessed by scientists) assimply larger versions of smaller eruptions (which havebeen witnessed and studied). For historic eruptions, TOMSdata show a positive correlation between the mass of SO2

and the mass of magma erupted (Blake 2003). Extrapolatingthis trend, the amount of SO2 that potentially could bereleased by a 2000–3000 km3 supereruption is about 3500to 20,000 × 109 kg of SO2.

The second method is to quantify the S concentrations inthe pre-eruptive magmatic liquid and gas, and then use thisinformation together with the mass fraction of the gasphase to calculate a total S content for the magma. In usingthis method, it is important to recognise that the partition-ing of S between the gas and the magmatic liquid is highlydependent on the oxidation state of the magma. In reducedmagmas the partition coefficient given by (mass of S ingas)/(mass of S in magmatic liquid) is about 1, but it isabout 1000 in more oxidized magmas (Scaillet et al. 1998).This means that most of the S in an oxidized magma canreside in the gas phase. Using this approach, and assuming5 wt% gas was present in the magma, Scaillet et al. (2004)estimated that the Bishop Tuff (USA) magma (1.3 × 1015 kg)held 0.085 wt% S; this would have produced 2.2 × 1012 kg ofSO2. For Toba, they suggest a S content of 0.022 wt% and,therefore, 1.4 × 1012 kg of S (2.8 × 1012 kg of SO2) wouldhave been released from the 2800 km3 of magma. In con-trast, the rhyolite magmas erupted from Yellowstone areconsiderably more reduced (Carmichael 1991) and cantherefore be expected to have low S yields. For Yellow-stone’s 2.0 Ma Huckleberry Ridge or 0.6 Ma Lava Creekeruptions (7 × 1015 kg of magma each; Mason et al. 2004),this approach predicts only 0.2 × 1012 kg of S (= 0.4 × 1012 kgof SO2), despite having unleashed roughly the sameamount of magma as Toba. Yellowstone’s supereruptionsmay therefore have each yielded merely 20 times theamount of SO2 produced by Pinatubo in 1991, or about

4242E L E M E N T S FEBRUARY 2008

Map showing areas covered by volcanic ash (approximately1 cm thickness) from eruptions at Pinatubo (Luzon, Philip-

pines) in 1991, Tambora (Sumbawa, Indonesia) in 1815, and Toba(Sumatra, Indonesia) ~74,000 years ago. Ash-fall volumes from historiceruptions such as Pinatubo (~2 km3, second biggest in 20th century)and Tambora (~25 km3, one of the biggest in the past thousand years)are dwarfed by those from supereruptions (Toba ~1000 km3).

FIGURE 1

three to four times as much as that produced by the 1783eruption of basaltic lava at Laki (Iceland) or the 1815 cli-mactic explosive eruption of Tambora.

Although there are considerable uncertainties in the calcu-lation of S emissions from ancient eruptions, the analysisabove indicates that a small volume of oxidized magma canrelease more S than a larger volume of reduced magma.

DURATION OF SUPERERUPTIONSAn important question in assessing the effects of asupereruption is “How long would such an eruption last?”This is a difficult question to answer as eruptive histories ofpast supereruptions are so different that it is probably notappropriate to propose a typical duration (Wilson 2008).What is significant is that the eruption rates (eruptiveintensity) during major explosive phases of supereruptionswere probably at least similar to the eruption rate at MountPinatubo in 1991, where 5 km3 of magma were emitted inthe 3.5-hour-long climactic phase, equivalent to almost

1 billion kilograms (~5 × 105 m3) of magma erupted eachsecond. The 24-hour-long Tambora eruption also had a sim-ilar eruption rate. However, it is expected that eruptionintensity and magnitude are linked (Sparks et al. 1997),such that supereruption rates might normally exceed 109 kgs-1 of magma. New work on giant ash clouds (Baines andSparks 2005) indicates that the intensity might approach1010 kg s-1 in the largest eruptions. One well-studied case(Wilson and Hildreth 1997) is the ~600 km3 Bishop Tufferuption, which is estimated to have lasted about 6 days withonly one short pause (an average eruption rate of ~3 × 109 kgs-1). Other supereruptions may have included several suchhigh-intensity eruptive phases spread over weeks to evenyears with periods of quiescence in between (Wilson 2008).

RECURRENCE OF SUPERERUPTIONSThe question of when the next supereruption might occuris also an important one. The last well-documentedsupereruption took place ~26,000 years ago, at Taupo volcano,New Zealand – the 530 km3 Oruanui eruption (Wilson2001, 2008). The most recent eruption approaching theextreme end of the size spectrum is considered to be Toba,which occurred 74,000 years ago. In fact, the number ofsupereruptions that have occurred in the past is quite small,but our knowledge base is incomplete, making prediction oftheir recurrence rate problematic. A recent survey of thelargest-magnitude explosive eruptions (Mason et al. 2004)shows them to have been very rare, with an average fre-quency of only one every 100,000–200,000 years. However,global average frequencies are not indicative of the real like-lihood of an eruption occurring in a particular area. Differentvolcanoes have different patterns of activity, and there havebeen cases when clusters of several very large eruptionsoccurred within the space of a few thousand years, implyingthat it is difficult to say how often supereruptions happen.

43E L E M E N T S FEBRUARY 2008

Products of large explosive eruptions: (A) giant eruptioncloud approximately 35 km high from Mount Pinatubo

on 15 June 1991 (Japanese Meteorological Agency satellite view; note200 km scale bar and outline of Philippine islands); (B) co-ignimbritecloud rising off a pyroclastic flow at the beginning of the main explosivephase on 15 June at Pinatubo (US Air Force photo taken from Clark AirBase, Luzon, Philippines); (C) ignimbrite-devastated countryside aroundPinatubo in 1992; a new 5 km2 caldera lies behind remnants of the vol-cano (PHOTO BY S. SELF); (D) part of Lake Toba caldera, Sumatra, with 300m high flat-topped cliffs in the background, which represent the calderarim capped by landscape-burying ignimbrite deposits produced by asupereruption 74,000 years ago; for comparison, the area of Tobacaldera is 3000 km2 (PHOTO BY S. BLAKE).

FIGURE 2

A

B

C

D

44E L E M E N T S FEBRUARY 2008

EFFECTS OF SUPERERUPTIONS

Near- to Mid-Field: Impact of Calderaand Pyroclastic Deposit FormationWe now consider the effects of very large eruptions, begin-ning at the local scale and extending outwards from the source.Caldera collapse may enlarge, or be encompassed within, aprevious collapse structure, depending on the prior historyof the volcano. Most supereruption calderas are partly back-filled with pyroclastic deposits (intracaldera ignimbrite).Caldera formation, which takes place catastrophically andengulfs everything on the surface, would destroy any man-made structures within an area of thousands of square kilo-metres. If it was an island volcano, the collapse could alsogenerate tsunamis (e.g. the 1883 Krakatau eruption, SundaStrait, Indonesia; Francis and Self 1983).

Ash remains airborne for only a few hours to days, duringwhich time it is an extreme hazard to anything flying,including aircraft (Casadevall 1993). Quite thin ash-fall layers(from a few to 10–15 cm) can cause roof collapse (depend-ing on construction style and standards, and wetting byrainfall), and as little as 1 cm of ash can cause severe dis-ruption to agricultural production if it falls in the growingseason. Satellite communication systems may well behighly vulnerable to interruption by ash clouds. Hydroelectricand nuclear power stations could be immobilised due to ashin water intakes, and power lines might be brought downby ash loading and associated electrostatic effects.

Pyroclastic flows are lethal and highly destructive to build-ings and other structures. Even areas covered by thin pyro-clastic flow deposits would be obliterated, as borne out bythe tragic effects of the small-scale flows that went throughSt. Pierre, Martinique, on May 8, 1902. Only 3 people out ofan estimated 30,000 survived, yet the deposits in the townwere only centimetres to a few metres thick. After a verylarge eruption, widespread pyroclastic flow deposits wouldhave to be contended with. These deposits would be manytens, up to several hundreds, of metres thick over areas ofthousands to tens of thousands of square kilometres, andthey would be thicker in valleys and on plains and thinnerover hills. All buildings and man-made structures, indeedall infrastructure, would be buried in thick pumice and ashdeposits and would be subjected to high temperatures(400–800°C) and acidic gases and leachates. Rain fallingonto fresh volcanic deposits can unleash secondary mud-flows (lahars) into rivers and stream catchments, leading topossible damming of rivers and ensuing break-out floods.Lahars caused the highest proportion of death and destruc-tion associated with the Pinatubo eruption, but in the yearsafter the volcanic activity died down.

The low bulk density of parts of most pyroclastic flows alsoenables them to cross water. During the 1883 eruption atKrakatau, pyroclastic flows crossed 40 km of the sea surfacebefore hitting the coast of southern Sumatra. However,most of the deaths associated with this eruption wereapparently caused by tsunamis generated when the pyro-clastic flows entered the sea. This serves as a reminder thata supereruption from an island or coastal volcano wouldprobably trigger a series of devastating sea waves.

Far-Field: Global Atmospheric Effects of LargeVolcanic EruptionsThe extensive deposits generated by a supereruption mayhave global consequences. Covering a continent-sized areawith white rhyolitic pumice and ash will increase the surfacealbedo, changing the land–atmosphere energy exchange. Ablanketing ash layer will also kill vegetation and alter sourcesand sinks involved in land–atmosphere gas exchange. If a

large mass of ash falls over a wide area of ocean, significantocean fertilization may occur, causing CO2 drawdown fromthe atmosphere.

More-direct global atmospheric changes can be wrought bythe volcanic gases injected into the stratosphere. Of these,sulfur gases (mainly sulfur dioxide, SO2) and sulfuric acid(H2SO4) aerosols are the most important atmosphericspecies, and their effects are quite well known (Robock2000; Self 2005). Volcanic SO2 released into the atmosphereis oxidized to form sulfuric acid aerosol particles duringreactions that rely on the Sun’s energy. The aerosol dropletsof partly frozen H2SO4 at low stratospheric altitudes(18–25 km), where conditions are very cold (~ -50°C) and atlow pressures, are in the right size range (0.1 to 1 µm) toeffectively backscatter and absorb incoming radiation fromthe Sun. Therefore, the net effect at the Earth’s surface andin the lowest atmosphere is usually cooling.

Well-studied volcanic aerosol events, such as that afterPinatubo in 1991, show how much aerosol is produced, andat what rate, from a known SO2 release. The Pinatuboaerosol cloud encircled the Earth in less than two weeks,and by three months had spread across much of the globe(FIG. 3). By the end of 1991, spreading polewards, theaerosol cloud had reached high-latitude regions, and it per-sisted in concentrations sufficient to influence Earth’s radi-ation budget for more than 3 years. Global temperatureswere 0.5°C below normal for two years after the eruption,temporarily offsetting global warming (Hansen et al. 1996).

The much larger S gas releases predicted for supereruptionsmay imply the formation of greater masses of aerosols, butwe do not know how efficient or how fast the conversion ofgas to aerosol particles in the atmosphere would be. Somework suggests that much more aerosol would form aftermassive SO2 emissions but that the droplets would be largerand would settle out of the stratosphere faster, thus limitingthe duration and magnitude of the effects (Pinto et al.1989). Other work suggests that the chemical reactionsforming the aerosols from huge SO2 clouds would initiallydehydrate the stratosphere, thus prolonging the time overwhich aerosols form (Bekki 1995). With this mechanism, itis possible that the gas-to-particle conversion would takeconsiderably longer than the usual 20–30 days, as exemplifiedby the carefully monitored post-Pinatubo aerosol cloud. Anunknown is the amount and role of water injected into thestratosphere by the eruption column. It is not yet possibleto predict with confidence the particle concentration of anaerosol cloud, or its longevity at various concentrations,after a very large eruption. The amount of SO2 that mightbe released is considerably larger than for any historic erup-tion and could lead to an aerosol cloud of unprecedentedopacity to incoming radiation. This was the premise of ear-lier assessments proposing a so-called ‘volcanic winter’(Rampino et al. 1988) after a very large eruption. Stratosphericaerosols will serve to catalyse ozone loss, increasing theground-level UV-B flux in high- to mid-latitude regions, theeffect lasting a few years after the eruption.

Recently, some of the first attempts were made to assess theeffects of a large stratospheric burden of sulfate aerosols.Timmreck and Graf (2005) used an atmospheric model withan SO2 gas input of 1700 × 109 kg (100 times that of thePinatubo eruption) from a source at 45° North, similar tothe location of Yellowstone volcano. They found that theseason of injection is important, with an almost global spreadof aerosols from an eruption in the mid-latitude NorthernHemisphere in summer; however, the spread of the aerosolcloud would be restricted to the Northern Hemisphere if theeruption occurred in winter. The results from this studysupport those of other climate model runs that simulate the

45E L E M E N T S FEBRUARY 2008

response to a huge eruption like Toba (Jones et al. 2005).Both studies indicate severe, short-term cooling, with globaltemperatures plummeting by as much as 10°C, followed bya longer-term (up to 10 years) recovery period. This, com-bined with much-reduced rainfall predicted by the climatemodels, could potentially kill off tropical rain forests.

SOCIETAL IMPACTS OF SUPERERUPTIONSWe now live in a complex, globally interrelated society thatis highly vulnerable to disruption, making the effects andconsequences of a large explosive eruption almost entirelydetrimental to mankind in the short term. In the past, majorhistoric eruptions have caused famine and disease epidemics(Tanguy et al. 1998). Today, almost 90% of the world’s pop-ulation lives in the Northern Hemisphere where most foodproduction is concentrated, making the Northern Hemisphereespecially vulnerable to the effects of major eruptions.These range from roof collapse due to the weight of an ashlayer to the possible disruptive effects of ash and aerosolclouds on satellite communications. Airborne ash wouldpresent problems to aviation, especially if the supererup-tion was of long duration. Ash would block roads, railwaysand airport runways, causing widespread problems. Ashwould also be a health hazard to the eyes and lungs; forexample airborne fine volcanic particulates can contain res-pirable particles of cristobalite (a form of silica) that can causesilicosis (Horwell et al. 2003; Baxter 2005). There are alsobound to be effects that we cannot yet anticipate.

The consequences of future large-scale eruptions are indetail very challenging to predict because of the variabilityof volcanic phenomena and the complex interlinking ofimportant societal necessities. Telecommunications and airtransport are likely to be extremely vulnerable, and theirdisruption would significantly compromise the effective-ness of disaster response in the wake of the largest-scaleeruptions. The cost of all natural disasters is rising steeply(Smolka 2006), and the effects on world financial marketswould likely be acute.

FINAL THOUGHTSVery large explosive eruptions, up to and includingsupereruptions, are a very small, but real, threat. Many aspectsof supervolcanic activity are not well understood as therehave been no historical precedents, and such eruptions mustbe reconstructed from their deposits. Neither is it straight-forward to locate or interpret any record of paleo-environ-mental upheavals in the years to decades after even the mostrecent supereruptions, several tens of thousands of years ago(Oppenheimer 2002).

Eruptions are unstoppable, and supereruptions are poten-tially long-lasting (at least several days of intense explosiveoutput from the volcano, and most probably several of thesephases spread out over weeks to even years). Further, theeffects of each explosive phase will be both immediate(widespread ash fall and pyroclastic flows) and prolonged(due to atmospheric aerosols and debris flows from reworked,unstable, fresh deposits). They will therefore persist and pres-ent problems for years after the last major explosive phase.The hazards posed by supereruptions differ from those dueto all other natural disasters: although extremely infre-quent, they probably present the greatest natural hazard tomankind in terms of the severity and longevity of impact –the ultimate geologic hazard.

Data from NASA’s Stratospheric Aerosol and Gas Experi-ment (SAGE II) satellite-mounted instrument show the

spread of Pinatubo’s sulfate aerosol cloud; the top-left panel shows thesituation before the 1991 eruption; other panels show the situation toJanuary 1994. Colours represent the optical depth (opacity) of the aerosolcloud, with blue being background values and red being the highestconcentrations. Note the global coverage by aerosols within a fewmonths of eruption. From McCormick et al. 1995; IMAGE COURTESY OF NASA

FIGURE 3

46E L E M E N T S FEBRUARY 2008

REFERENCESBaines PG, Sparks RSJ (2005) Dynamics of

giant volcanic ash clouds from supervol-canic eruptions. Geophysical ResearchLetters 32: L24808,doi:10.1029/2005GL024597

Baxter PJ (2005) Human impacts of volcanoes.In: Marti J, Ernst GGJ (eds) Volcanoesand the Environment. CambridgeUniversity Press, Cambridge, pp 273-303

Bekki S (1995) Oxidation of volcanic SO2:A sink for stratospheric OH and H2O.Geophysical Research Letters 22: 913-916

Blake S (2003) Correlations betweeneruption magnitude, SO2 yield, andsurface cooling. In: Oppenheimer C, PyleDM, Barclay J (eds) Volcanic Degassing.Geological Society of London SpecialPublication 213, pp 371-380

Bluth GJS, Rose WI, Sprod IE, Krueger A(1997) Stratospheric loading of sulfurfrom explosive volcanic eruptions.Journal of Geology 105: 671-683

Carmichael ISE (1991) The redox states ofbasic and silicic magmas: a reflection oftheir source regions? Contributions toMineralogy and Petrology 106: 129-141

Casadevall T (1993) Volcanic hazards andaviation safety: lessons of the past decade.FAA Aviation Safety Journal 2: 3-11

Francis PW, Self S (1983) The 1883 eruptionof Krakatau. Scientific American 249:172-188

Hansen J, Sato M, Ruedy R, 27 others (1996)A Pinatubo climate modelling investigation.In: Fiocco G, Fua D, Visconti G (eds)The Mount Pinatubo Eruption: Effectson the Atmosphere and Climate. NATOAdvanced Study Institute Series 14,Springer-Verlag Heidelberg, pp 233-272

Horwell CJ, Sparks RSJ, Brewer TS, LlewellinEW, Williamson BJ (2003) Characterizationof respirable volcanic ash from theSoufrière Hills volcano, Montserrat, withimplications for human health hazards.Bulletin of Volcanology 65: 346-362

Jones GS, Gregory JM, Stott, PA, Tett SFB,Thorpe RB (2005) An AOGCM simulationof the climate response to a volcanic super-eruption. Climate Dynamics 25: 725-738

Lowenstern JB, Hurwitz S (2008) Monitoringa supervolcano in repose: Heat and volatileflux at the Yellowstone Caldera. Elements4: 35-40

Mason BG, Pyle DM, Oppenheimer C (2004)The size and frequency of the largestexplosive eruptions on Earth. Bulletinof Volcanology 66: 735-748

McCormick MP, Thomason LW, Trepte C(1995) Atmospheric effects of the MtPinatubo eruption. Nature 373: 399-404

Miller CF, Wark DA (2008) Supervolcanoesand their supereruptions. Elements 4: 11-16

Newhall CG, Dzurisin D (1988) HistoricalUnrest at Large Calderas of the World.USGS Bulletin 1855, 2 volumes, 1108 pp

Oppenheimer C (2002) Limited global changedue to the largest known Quaternaryeruption, Toba ≈ 74 kyr BP? QuaternaryScience Reviews 21: 1593-1609

Pinto JP, Turco RP, Toon OB (1989) Self-limiting physical and chemical effectsin volcanic eruption clouds. Journal ofGeophysical Research 94: 11165-11174

Pyle DM (2000) The sizes of volcaniceruptions. In: Sigurdsson H et al. (eds)The Encyclopedia of Volcanoes. AcademicPress, London, pp 263-269

Rampino MR (2002) Supereruptions asa threat to civilizations on Earth-likeplanets. Icarus 156: 562-569

Rampino MR, Self S, Stothers RB (1988)Volcanic winters. Annual Review of Earthand Planetary Sciences 16: 73-99

Robock A (2000) Volcanic eruptions andclimate. Reviews of Geophysics 38: 191-220

Rose WI, Chesner CA (1987) Dispersal ofash in the great Toba eruption, 75 ka.Geology 15: 913-917

Scaillet B, Clemente B, Evans BW, PichavantM (1998) Redox control of sulfur degassingin silicic magmas. Journal of GeophysicalResearch 103: 23937-23950

Scaillet B, Luhr JF, Carroll MR (2004)Petrological and volcanological constraintson volcanic sulfur emissions to theatmosphere. In: Robock A, Oppenheimer

C (eds) Volcanism and the Earth’sAtmosphere. American Geophysical UnionGeophysical Monograph 139, pp 11-40

Self S (2005) Effects of volcanic eruptionson the atmosphere and climate. In: MartiJ, Ernst GGJ (eds) Volcanoes and theEnvironment. Cambridge UniversityPress, Cambridge, pp 152–174

Smolka A (2006) Natural disasters andthe challenge of extreme events: riskmanagement from an insurance perspective.Philosophical Transactions of the RoyalSociety A364: 2147-2165

Sparks RSJ, Bursik MI, Carey SN, Gilbert JS,Glaze LS, Sigurdsson H, Woods AW (1997)Volcanic Plumes. Wiley and Sons,New York, 574 pp

Sparks RSJ, Self S, Grattan JP, OppenheimerC, Pyle DM, Rymer H (2005) Super-eruptions: global effects and future threats.Report of a Geological Society of LondonWorking Group, The Geological Society,London, 24 pp (http://www.geolsoc.org.uk/template.cfm?name=Super1)

Tanguy J-C, Ribière C, Scarth A, Tjetjep WS(1998) Victims from volcanic eruptions: arevised data base. Bulletin of Volcanology60: 137-144

Timmreck C, Graf H-F (2005) The initialdispersal and radiative forcing of a mid-latitude super-eruption: a NorthernHemisphere case study. AtmosphericChemistry and Physics Discussions 5:7283-7308

Wilson CJN (2001) The 26.5 ka Oruanuieruption, New Zealand: an introductionand overview. Journal of Volcanologyand Geothermal Research 112: 133-174

Wilson CJN (2008) Supereruptions andsupervolcanoes: Products and processes.Elements 4: 29-34

Wilson CJN, Hildreth W (1997) The BishopTuff: New insights from eruptive stratigra-phy. Journal of Geology 105: 407-439

Zhang Y, Xu Z (2008) “Fizzics” of bubblegrowth in beer and champagne. Elements4: 47-49 .

It will be necessary to develop strategies to minimise andcope with the effects of future major eruptions. The economiccost of recovery from any future large-scale eruptions willbe a major burden on society. As airborne ash and atmos-pheric sulfate aerosols will bring about the most widespread,long-lasting, and generally hazardous effects of the nextlarge explosive eruption, it is essential to carry out furtherstudies with Earth system models (e.g. coupled atmos-phere–ocean general circulation models) to evaluate thepotential effects on climate and weather and to assess otherpossible environmental effects.

Other critical matters that are poorly understood includehow long the build-up to such an eruption would be andwhether the size and course of events in the impendingeruption could be predicted. A large eruption from a geo-physically monitored volcano might be predictable to a cer-tain degree, and precursory activity could last for years, ifnot decades (see Newhall and Dzurisin 1988; Lowensternand Hurwitz 2008). The difficulty would be to predict whetherinitial activity might escalate into a catastrophic eruptivephase. There may also be false alarms, with the major phase

of an eruption following after years of smaller-scale activity.At present there is no scientific or evidence-based way todetermine whether precursor eruptions might be heraldinga very large outburst rather than a smaller-magnitude eruption.

Of concern is a situation where a volcano that is currentlyunrecognized as a potential large-eruption site, or that isevolving towards its first supereruption, or that is not mon-itored, becomes restless. In these cases scientists and/or thegovernment concerned may not recognize the signs. Thisuncertainty underlines the fact that we need to know muchmore about past supereruptions: which volcanoes producedthem, what the ages are, what their true size was, and whattypes of deposits were produced.

ACKNOWLEDGMENTSWe thank John Pallister, Ian Parsons, Steve Goodbred,Tonya Richardson and Tenley Banik for reviewing the man-uscript, and Calvin Miller and David Wark for much help-ful advice and editorial support. .