GEOPHYSICALRESEARCH LETTERS, VOL. 19, NO. 2, PAGES151-154, JANUARY 24, 1992

GLOBALTRACKING OF TItE SO2CLOUDS FROM THE JUNE,1991 MOUNT PINATUBO ERUPTIONS

GreggJ.S. Bluth UniversitiesSpace Research Association, NASA/Goddard Space Flight Center

Scott D. Doiron HughesSTX Corporation, NASA/Goddard Space Flight Center

CharlesC. Schnetzler,Arlin J. Krueger, and Louis S. Walter EarthSciences Directorate, NASA/Goddard Space Flight Center

•Ab•tract.The explosiveJune 1991 eruptionsof Mount anomalouslyhigh ozone values were noticed over Mexico. Pinatuboproduced the largestsulfur dioxide cloud detected Thesehigh values were caused by sulfurdioxide interference, bythe Total Ozone Mapping Spectrometer (TOMS) during andit thereforebecame necessary to separatethe its13 yearsof operation:approximately 20 milliontons of volcanogenicSO2 signal from the ozone data [Krueger, SO2,predominantly from the cataclysmic June 15th eruption. 1983]. Examinationof absorptioncoefficients for SO2in the TheSO2 cloud observed by the TOMS encircledthe Earthin spectralrange measured by theTOMS led to the about22 days(~21 m/s); however, during the f•t threedays developmentof analgorithm to quantifythe SO2 amounts theleading edge of theSO2 cloud moved with a speedthat [Krueger,1985]. Sincethen, all eruptions(including 1978- averaged~35 m/s. Comparedto the 1982E! Chich6n 1982data) with potential for measurableamounts of erupted eruptions,Pinatubo outgassed nearly three times the amount SO2have been routinely examined. of SO2during its explosivephases. The maincloud As a monitor of volcanism,the TOMS insmmaentis best straddledthe equator within the fn'st two weeksof eruption, usedto detectand track SO2 emitted from the explosive whereasthe E! Chich6ncloud remained primarily in the phasesof eruptions.The TOMS observessulfur dioxide northernhemisphere. Our measurementsindicate that Mount primarilyin thestratosphere, and its detectionlimit of a given Pinatubohas produced a muchlarger and perhaps longer- eruptioncloud is about5 kilotons(kt) SO2. Major lastingSO2 cloud; thus, climatic responses to thePinatubo advantagesof theTOMS areits capabilityto detectexplosive eruptionmay exceed those of E1Chich6n. eruptionsvirtually anywhere on the sunlitEarth within 24 hoursand its abilityto measurethe completespatial extent of Introduction large,explosive eruptions. Previous volcanic events examinedusing the TOMS instrumentinclude the 1982 E1 Mount Pinatubois an andesiticisland arc volcano, located Chich6neruptions [Krueger, 1983], Nevado del Ruiz in 1985 onsouthern Luzon Island, Philippines. Wolfe andSelf [Kruegeret al., 1990],the 1989Redoubt activity [C. [!983] brieflydescribe the volcano, and cite the most recent Schnetzler,unpublished manuscript, 199I], andthe 1991 eruptionas occurring approximately 635 yearsearlier (from CerroHudson eruptions [Doiron et al., !991]. carbon-14dating of mudflowdeposits), but noted that Pinatubohad never been studied in greatdetail and that there Satellite Data mayhave been more recent, undocumented eruptions. In June1991 the volcano erupted in a seriesof minor The TOMS instrumentdaily observationsof the Mount explosionsleading up to a cataclysmiceruption June 14-15 Pinatuboeruptions are summarizedin Table 1 andin Figure [Lynchet al., 1991]. A largeamount of solidand gaseous la-d. Total columnamounts of SO2 are givenin unitsof materialwas ejected from the volcano, and a significant milli arm-cm.This unit represents the amountof gaswhich proportionof theash was deposited in theSouth China sea. is affectingthe reflection of ultravioletlight througha Thecombined tephra and pyroclastics were estimated at 3-5 scanningcolumn (from the satelliteto the Earth'sreflecting kin3dense rock equivalent [Scott et al., !991]. surface),given in termsof the one dimensionalthickness of The TOMS instrument on board the Nimbus-7 satellite has the puregas layer at STP. The massof SO2is calculatedby providedglobal SO2 and ozone data since 1978 by measuring integratingover the cloudarea to obtaina volume,then theultraviolet albedo, the ratio of backscatteredEarth convertingto tons. Typicalvolcanic SO2 clouds detected by radianceto incomingsolar irradiance. The satellite is in a the TOMS rangefrom 20 to severalhundred milli am-cm. polarsun-synchronous orbit and crosses the equator every 26 The error estimationfor the TOMS SO2 valueshas been degrees(2900 kin) of longitude atlocal noon, observing the describedby Kruegeret al. [!990]. The totalerror in wholeearth once a day(13.7 orbits/day). The TOMS was reportedvalues, :t: 30%, is basedon uncertaintiesin the designedwith the intention of globallymapping total ozone algorithmcalculation, absorption level measurements,and only,but after the eruption of E! Chich6nin April 1982 backgroundnoise.

EruptionCloud Chronology Copyright1992 by theAmerican Geophysical Union. Papernumber 91GL02792 The initial sulfurdioxide detected by the TOMS 0094-8534/92/91GL-0279.2503.00 instrumentfrom Mount Pinatubooccurred as three small SO2

151 152 Bluthet al.: TrackingSO2 Clouds from Mt. Pinatubo

Table1. Summaryof TOMSData for. the 1991 Mount Pinatubo Eruption Clouds 'Image ArealExtent Measured Height Geographic Comments Date (km2) SO2(kt)* Position June 12 100 25 trop Westcoast of LuzonIsland Cloudobserved for 3 days;on June 13 measured 110 kt June 13 100 15 trop Westcoast of LuzonIsland New cloudobserved for 1 day June 14 -no new activitydetected- June 15 7500 450 trop/strat SouthChina Sea, from 10 to 15øN New, 1600km longcloud over the volcano;observed 1 day June16 3.2 x 106 15,500 strat Centered over South China Sea at New discretecloud from major minimum -15øN eruption,200 km eastof volcano June17 4.8 x 106 18,500 strat Lead cloudover tip of India; main Main cloud2000 km from origin; cloud over south Thailand at 10øN overall lengthof clouds4400 km June18 7.5 x 106 16,000 strat From Malaysia to Gulf of Aden at Main cloud3000 km from origin; -10øN latitude total cloudis 7000 km in length June19 7.4 x 106 14,000 strat Lead cloud over Sudan; main cloud Main cloud4300 km from origin; minimum over northeast Indian Ocean leadinglobe breaking apart June20 8.6 x 106 14,500 strat Lead clouds over E. Africa; main Main cloud4500 km from origin, cloudover equatorialIndian Ocean 6000 km in length June23 15.4 x 106 14,000 strat Lead cloud over Mali; main cloud Main cloud10,000 km long,main from Sumatra to central Africa SO2 massno longerdiscernable June30 54.5 x 106 12,000 strat From Indonesia to west Pacific Main cloudover 16,000km long; Ocean, 10øSto 20øN even, low level SO2 distribution * SO2calculated from near real-time TOMS '"data; actual value• Cohld'"be "larger as discussed in the text. On June 16 and June19 theTOMS instrumentexperienced problems in the areaof theSO2 cloud, where no datawere reported.

cloudserupted from June 11-14. The first cloud was detected the SO2cloud was over the Gulf of Aden, correspondingto on June12th (i.e., includingany eruptionactivity from noon an 3-day averagespeed of 35 m/s. The cloud'smovement June11 to noonJune 12). This cloudmeasured 100 km 2 in wasprimarily westward, with somespreading slightly to the area,and contained -25 kt SO2. By June13th the cloudhad southtowards the equator.The SO2 estimatefor the 18th drifted 1100 km to the west, over central Vietnam, and now was 16,000 kt. measured110 kt SO2. By June 14th,the cloudcould be The June23rd imagemarked a changein thephysical barelydiscerned over the easternIndian Ocean at about configurationof theSO2 cloud (Figure lc). The cloudno 15øN, and was not seen thereafter. A secondcloud of 100 longerconsisted of a mainconcentrated mass and a leading km2area and less than 15 kt SO2was detected June 13th lobe or leadingcloud. It now extended10,000 km from over the westernedge of Luzon island,but was only observed Indonesiato centralAfrica in a fairly uniformdistribution of for one day. A third cloud was detectedon June 15th, SO2,covering an areaof about15 millionsquare kilometers. measuring7500 km 2 in areaand stretching 1600 km The leadingcloud which had sheared away from the main westward from Mount Pinatubo to southern Vietnam. T•,e cloudwas largely dispersed below the TOMS detectionlimit, SO2cloud was composed of at leastthree distinct leavingonly a tracevisible over westernAfrica. The cloud concentrationsprobably corresponding to individualeruption crossedthe equatorto asfar as 10øSlatitude. The trailing pulsesoccurring June 14th. This cloudtotaled approximately endof the cloudremained nearly fixed over Sumatra.The 450 kt SO2,but on subsequentdays it hadeither dispersed relativelylower cloudSO2/background ratios by this time belowdetection levels or was maskedby themajor eruption madequantitative measurements more difficult; the estimate cloud. of SO2 tonnagefor the June23 cloudswas -14,000 kt. The cataclysmiceruption of June15th began before noon Figure 1d showsthe SO2 cloudon June30th, two weeks andlasted until the followingmorning [Lynch et al., 1991]. after the main eruption.The cloudis spreadover 16,000km The timingof the eruptionwas suchthat it was not detected in length,straddling the equator, reaching from 10øSto 20øN. by theTOMS until the 16th. Figure la showsthat in The cloudarea extends over 50 million squarekilometers. approximately24 hoursthe centerof the SO2cloud had The leadingedges of the visiblecloud have reached the drifted 1000 km to the WSW as a discrete mass. The longitudeof California,and the trailingedge (out of the measuredamount of SO2 in this cloud is 15,500 kt but, picture)remains mired over Indonesia.This cloudmeasured becauseof datalosses and detectorsaturation, the actual 12,000kt SO2; thus,after 15 daysthe Pinatubocloud still amountmust be greaterthan this. containedroughly 60% of its originalSO2. On theJune 17th image, approximately 36 hoursafter the The SO2 cloud remainedvisible to the TOMS instrument endof thecataclysmic eruption, the SO2cloud as a whole longenough to observeits completecircuit of the Earthin 22 haddispersed enough so thatall the individualcolumn values days. This pacewas virtuallyidentical to the E1 Chich6n couldbe measuredto yield a moreaccurate value: 18,500kt SO2cloud in 1982 (althoughin bothcases SO2 at lower of SO2. concentrationsprobably made the round trip at a fasterpace). By June18th the SO2cloud stretched 6500 km in length, Discussion with a concentratedmass connected to a longleading edge (Figurelb). The mainportion was centered over the Bay of Theeruption cloud from Pinatubo is by far thelargest that Bengal,about 3300 km fromthe source. The leadingedge of we havedetected since the TOMS instrumentbegan Bluthet al.: TrackingSO2 Clouds from Mt. Pinatubo 153

Fig. 1. False-colorimages of Mount PinatuboSO2 clouds produced from TOMS data. SO2volumes over columnareas are in unitsof milli atm-cm(see text). Scalesvary to compensatefor clouddispersion. (a) June16th. Linesare 10 degreesof latitudeand longitude. Cloudcenter values exceed the TOMS detectionlimits, and somedata loss occurred over the northern edgeof the cloud. (b) June18th. Linesnow denote30 degreeslatitude and longitude. (c) June23rd. (d) June30th. collectingdata in 1978. In Table 2 we comparesome of the TOMS datafor the first two weeksof the eruptionhave physicalcharacteristics of Pinatuboto: Novarupta/Katmaiin beenused to calculatethe dispersion rate of SO2. An 1912,the lasteruption of a comparablesize in the northern exponentialcurve fit to the datayields an e-foldingtime of hemisphere;and E1 Chich6n,1982 andNevado del Ruiz, 35 days;however, in lightof thepreliminary nature of the 1985,two recenteruptions which have also been observed by data,the difficultyof measurementof spatiallylarge clouds, the TOMS. All four volcanoes are in island arc tectonic and the datadrop-out and saturationproblems mentioned settings;Novampta erupted mostly rhyolitic lava, but the earlier,this value shouldbe regardedas tentative. otherthree volcanoes were andesiticin composition. It is generallyaccepted that El Chich6nproduced a Combiningthe measured SO2 from the June 12, June 13, measurableclimate signal, but the magnitudeof thateffect is June15, and June 17 (whichmay contain some of the450 kt measuredJune 15) clouddata gives a sulfurdioxide total of Table2. A TOMS Comparisonof MountPinatubo to Other 19,100 kt. We stressthat this total is measured SO2: LargeEruptions dispersionof thegas cloud, conversion of SO2to sulfuric Novarupta/ E1 Nevado Mount acid,and saturation of the TOMS detectorall suggestthat the Katmai Chich6n del Ruiz Pinatubo actualexplosive output of SO2from Pinatubo could be 1912 1982 1985 1991 higher.The 18,500kt cloudwas measured-36 hours after SO21 5,200- 7,003 750 •0;000 ' thecataclysmic eruption ended. The SO2loss over the next 20,000 fivedays suggests an averageloss of 1,000- 1,500kt SO2 ejecta2 (g) 3.4x1016 3.0x1015 4.8x1013 1.0x1016 perday. Therefore,we estimatethat the total amount of SO2 SO2/ejecta 0.0002 - 0.0023 0.015 0.0019 emittedfrom the June 14-15 explosive eruptions of Mount mass ratio 0.0006 VEI 3 6 4-5 3 5-6 Pinatubowas approximately 20,000 kt. Thetotal SO2 from Mount Pinatubo is nearlythree times 1NoVarUptaS02rang• 'f4:om: (low) petrolog4c estima teof' the7 milliontons SO2 'measured by theTOMS instrument Palaisand Sigurdsson [1989]; (high) ice-coreacidity fromthe E1 Chich6n eruption (note that we have revised this measurementsof Hammer et al. [ 1980]. Others are TOMS valueupward from the original estimate, 3.3 million tons, of measuredamounts during explosive eruption phases. Krueger,1983). Althoughthe SO2 production of Novarupta 2Ejecta(dense rock equivalents) for Novarupta:midrange valueof Hildreth [ 1987];E1Chich6n: Sigurdssonet al. wasnot directly measured, indirect methods suggest it [1984], andCarey and Sigurdsson [1986]; Ruiz: Naranjoet produceda similar magnitude, 5,200-20,000 kt, of sulfur al. [1986], andCalvache [ 1990]; Pinatubo: midrangevalue dioxide[Palais and Sigurdsson, 1989; Hammer et al., 1980]. of Scott et al. [1991]. Massratios of explosivelyoutgassed SO2 to solidejecta, 3VEI estimatesfrom Simkin et al. [ 1981];Smithsonian assuminganejecta density of 2.5g/cm 3, range over a factor InstitutiordSEAN[ 1989];Pinatubo VEI estimatedusing of thirtyamong the four volcanoes. parametersof Newhalland Self [ 1982]. 154 Bluthet al.: TrackingSO2 Clouds from Mt. Pinatubo

lesscertain: from 0.2 to 0.5øC[Robock, 1984; Angell, 1988; Hildreth,W., New perspectiveson theeruption of 1912in the Massand Portman, 1988]. The Pinatuboeruption emplaced Valley of Ten ThousandSmokes, Katmai National Park, muchmore sulfur dioxide into the stratospherethan did E1 Alaska, Bull. Volc., 49, 680-693, 1987. Chich6n,and the SO2 was distributedover the Earth by a Krueger,A.J., Sightingof E1Chich6n sulfur dioxide clouds morewidespread and possibly longer-lasting cloud. The with the Nimbus7 Total OzoneMapping Spectrometer, eruptionof Mount Pinatubooffers the excitingprospect to Science,220, 1377-1378, 1983. observeand studypotential climatic responses. Krueger,A.J., Detection of volcaniceruptions from space by their sulfur dioxide clouds, Am. Inst. Aero. Astro., 23rd Conclusions AerospaceSciences Meeting, AIAA-85-OlO0, Reno, Nevada,5 pp., 1985. Thecataclysmic eruption of MountPinatubo on June 15- Krueger,A.J., L.S. Walter, C.C. Schnetzler,and S. D. 16, 1991 emitted18,500 kt of SO2 asmeasured 36 hourslater Doiron, TOMS measurementof the sulfur dioxide emitted by theTOMS instrument. Based on thedecrease of SO2 duringthe 1985 Nevadodel Ruiz eruptions,J. Volc. exhibitedby thecloud over the following days, we estimate Geotherm.Res., 41, 7-15, 1990. thatthe total SO2 erupted by thecataclysmic eruption was Lynch,J.S., G. Stephens,and M. Matson,Mount Pinatubo: a approximately20,000 kt. Theerupted SO2 cloud appeared as satelliteperspective of theJune 1991 eruptions, Geophys. a singlepulse and the main cloud mass drifted WSW at Res. Lett., this issue, !991. approximately20 m/s,although the leading edge of thecloud Mass,C.F. andD.A. Portman,Major volcaniceruptions and driftedahead at nearlytwice this velocity. The SO2cloud climate: a critical evaluation,J. Clim., 2,566-593, 1989. remaineddrifting in a concentratedmass for sevendays after Naranjo,J.L., H. Sigurdsson,S.N. Carey,and W. Fritz, whichit graduallyspread into a broader,evenly dispersed Eruptionof the Nevadodel Ruiz volcano,Colombia, on 13 cloud. After two weeksthe visibleSO2 cloudhad spread November1985: tephrafall and!ahars, Science, 233, aboutñ 20ø in latitudeabout the equatorand stretched nearly 961-963, 1986. continuously10,000 km fromIndonesia to theGahtpagos Newha!l,C.G. andS. Self,The volcanicexplosivity index Islands.The TOMS-observed portion of thecloud encircled (VEI): an estimateof explosivemagnitude for historical theEarth in 22 days(~21 m/s). volcanism,J. Geotherm.Res., 87, 1231-1238, 1982. The SO2tonnage of Mount Pinatubowas the greatestever Palais,J.M. andH. Sigurdsson,Petrologic evidence of recordedin 13 yearsof TOMS operation,almost three times volatileemissions for majorhistoric and prehistoric thatof the 1982E1 Chich6neruption (the nextlargest eruptions,AGU Monograph52, 31-53, 1989. eruptionobserved by theTOMS). The sulfurdioxide Robock, A., Climate model simulationsof the effects of the injectedby E1Chich6n into the stratospheremay have caused E1Chich6neruption, Geol. Int., 23-3, 403-414, 1984. upto 0.5øCcooling in thenorthern hemisphere the following Scott,W.E., R.P. Hoblitt, J.A. Daligdig, G. Besana,and B.S. year;the eruption of MountPinatubo has injected a Tubianosa,15 June!991 pyroclasticdeposits at Mount significantlygreater amount of SO2into the stratosphere. Pinatubo,Philippines (abstract), EOS Trans.AGU, 72, 61- Thus,within the next 12 monthswe shouldexpect to seea 62, 1991. measurableclimatic signal originating from the Mount Sigurdsson,H., S.N. Carey,and J.M. Espindola,The 1982 Pinatuboeruption. This natural experiment should provide a eruptionsof E1 Chich6nvolcano, Mexico: stratigraphyof testof the accuracyof clLmatemodels. pyroclasticdeposits, J. Volc.Geotherm. Res., 23, 11-38, 1984. Ackn0wle0gements.We aregrateful to theGlobal Simkin,T., L. Siebert,L. McClelland,D. Bridge, C. VolcanismProgram of the SmithsonianInstitution for their Newhall, andJ.H. Latter, Volcanoesof the WorM: A timelydissemination of Pinatubodata, J. Sissalaand other RegionalDirectory, Gazetteer,and Chronologyof membersof the GE/RCA servicegroup for providing VolcanismDuring theLast 10,000 Years,240 pp., Nimbus-7 data setson shortnotice, J. Williams of STX and HutchinsonRoss, Stroudsburg, PA, !981. A. Oakesof Code636 at GSFCfor promptlyresponding to Smithsonian!nstitution/SEAN, Global Volcanism 1975- ourrequest for nearreal-time satellite data processing. 1985,657 pp., Prentice-Hall,Englewood Cliffs, NJ, and AGU, Washington,DC, 1989. References Wolfe, J. and S. Serf, Structurallineaments and Neogene volcanismin southwesternLuzon, in The Tectonicand Angell,J.K., Impact of E1Nifio on the delineationof troposphericcooling due to volcaniceruptions, J. GeologicEvolution of SoutheastAsian Seas and Islands, Geophys.Res., 93, 3697-3704, 1988. part 2, editedby D.E. Hayes,pp. 157-172,AGU Calvache,M.L., V, Pyroclasticdeposits of the November13, Monograph27, 1983. 1985eruption of Nevadodel Ruiz volcano,Colombia, J. G. Bluth, S. Doiron, and C. Schnetzler,NASA/GSFC, Volc. Geotherm.Res., 41, 67-78, 1990. Code 921, Greenbelt,MD 20771 Carey,S. andH. Sigurdsson,The 1982eruptions of E1 Chich6nvolcano, Mexico (2): observationsand numerical A. Krueger,NASA/GSFC, Code 916, Greenbelt,MD 20771 modellingof tephra-falldistribution, Bull. Volc.,48, 127- 141, !986. L. Walter,NASA/GSFC, Code 920, Greenbelt,lVID 20771 Doiron, S.D., G.J.S. Bluth, C.C. Schnetzler,A.J. Krueger, andL.S. Walter,Transport of CerroHudson SO2 clouds, (Received:September 30, 1991; EOS Trans. AGU, 72, 489-498, 1991. accepted:October 29, 1991)