Bul letin of the Global Vol can ism Net work Vol ume 29, Num ber 7, July 2004

Galeras (Co lom bia) 7 June 2002 and 16 July 2004 ash emissions ; the latter leads into an eruptive epi sode ..2

Tengger Cal dera (In do ne sia) Video of the 8 June eruption; minor ash plumes through 18 July ...... 5

Manam (Pa pua New Guinea) Weak to moder ate white vapor emissions during July ...... 5

Pago (Pa pua New Guinea) Mostly quiet ex cept for thin white vapor emissions in July...... 6

Ulawun (Pa pua New Guinea) Thin white-and-blue vapor emissions but other wise quiet dur ing July ...... 6

Rabaul (Pa pua New Guinea) White vapor emissions and low level seismic ity at Tavurvur in July 2004 ....7

Yasur (Vanuatu) Ele vate d seismic and eruptive activ ity af ter March 2004; emissions from three vents.....7

Edi tors: Rick Wunderman, Ed ward Venzke, and Gari May berry Vol unteer Staff: Jessica Ball, Jacquelyn Gluck, and Susan Nasr

Global Vol canism Program · National Museum of Natu ral His tory, Room E-421, PO Box 37012 · Wash ington, DC 20013-7012 · USA Tele phone: (202) 633-1800 · Fax: (202) 357- 2476 · Email: gvn@vol cano.si.edu · URL: http://www.vol cano.si.edu/

Subscrip tions are provided by the Ameri can Geo physical Union (see the box on the last page for details). Data are prelimi nary and sub ject to change; contact the original source or the Global Volcan ism Program bef ore using. 2 Smithsonian Institution — Bulletin of the Global

var ied and was larg est in the most recent quar ter. The range Galeras of depths for the VT earthquakes is roughly com para ble, al- though in the first quarter of 2004 these earthquakes had fo- SW Co lom bia cal depths only down to 12 km, com pared to as deep as 15 1.22°N, 77.37°W; sum mit elev. 4,276 m and 16 km in the other quarter s shown. For the 2004 quar- All times are lo cal (= UTC - 5 hours) ter, six epi sodes of tremor were recorded. Although fewer epi sodes oc curred than for the other quarter s shown in the This re port cov ers ac tiv ity on Galeras vol cano af ter cal- table, they re leased an ap pre ciable amount of en ergy. Spec- endar year 2002 (Bul le tin v. 28, no. 2) and through July tral anal y sis gen er ally sug gested a fun da men tal fre quency 2004. Towards the end of this inter val, on 16 July 2004, a of 4.3 Hz. new erupti ve epi sode be gan. In contra st to the 2004 events, In early 2003, LP signals conti nued to be present in the the inter val from 1994 to June 2004 was charac ter ized by re cord, al though their clas si fi ca tion was made dif fi cult by rel ative quiet, ex cept for a small ash emission from a sec- their atyp i cal sig na tures. Their fre quency spec tra showed ondary crater on 7 June 2002. Since 1997 INGEOMINAS peaks betwee n 10 and 16 Hz. Someti mes these events were has been part of a re search pro ject called ‘The precede d by one or more small-am pli tude precur sor signals , multiparameter station at Galeras vol cano’ that was de vel - which ap peared to have very sim ilar wave forms. The fre- oped with the Germ an group, Bundesanstalt für quencie s were sta ble over time and from one stati on to an- Geowissenschaften und Rohstoffe (BGR). The stati on in- other, indi cat ing proces ses relat ed to the source rather than cludes the moni tor ing of fumarolic gas, electro m agneti c to the path or the sta tion site. fields, broad band seis mic ity, ther mal im ag ery, and other The W sec tor of the ac tive cone conti nued to show the param eter s (Seidl and others, 1998). Most instru m ents were high est fumarole tem per a tures. INGEOMINAS mea sured func tion ing dur ing the re cent pe riod of ac tiv ity. fumarole tem pera ture s on the acti ve cone in March 2003 INGEOMINAS re ported that during Janu ary-March and Janu ary 2004, and at both times they were cooler than 2004 Galeras volca nism was at very low levels , with persis - those measured in 2002. Spot measure m ents in 2002, 2003, tent gas emissions from differ ent foci on the ac tive cone, and 2004 were reporte d for two fumarolic areas : Deformes parti cu lar ly on its W side. There were 60 vol cano-tectoni c fumaroles (~ 50 m outside the main crater´s SSW rim, (VT) earthquakes , with many center ed ~ 3 km NE of the ac - 118EC, 85EC, and 86EC, re spec tively) and Chavas tive cone, several disperse d about the region, and a few epi- fumarole (344EC, 267EC, and 310EC). center s within 2 km of the sum mit. Magni tudes based on Commenc ement of 2004 erupti ons. The most re cent the dura ti on of the signal coda (Md) varied be tween 0.1 and phreatic erupti on before 16 July 2004 took place on 7 June 2.8. 2002 (Bul le tin v. 28, no. 2). The erupti on on 16 July 2004 Res idents felt three earthquakes in Pasto. Two on 27 was preceded by a de crease in the amount of CO2 re leased Janu ary occurred at 1511 and 2147 and another on 30 Janu - at La Joya fumarole (W side of the cone). The decrease be - ary at 0018. Their respec tive local magni tudes (ML) were 2. gan on 6 June and lasted unti l the gas sensor stopped work- 9, 3.1, and 2.3. All had epi center s 4-5 km NNE of Galeras. ing on 26 July 2004. On 27 June the seism ic acti vit y picked Table 1 com pares seism icit y for the first quarter of 2004 up. The earthquakes exhib it ed high frequen cie s, and they with the last quarter in 2002 and the first in 2003. The num - under went rapid atten u a ti on in both time and space. The ber of VT events clearly dropped, but their energy relea se VT and LP events were at shal low lev els (less than 2 km).

Vol cano-tec tonic Earth quakes Tremor Quar ter Long-pe riod Earth quakes Count En ergy (1015 ergs) Depth be low summ it Count En ergy (1014 ergs)

Oct-Dec 2002 197 2.9 0.2-16 km 209 27 1,541 Jan-Mar 2003 126 0.49 0.2-15 km 19 0.03 104 Jan-Mar 2004 60 6.7 0.3-12 km 6 12 1

Table 1. Cum u lative seism icity in the given three-month inter vals (quarter of a year) at Galeras. The sec ond through fourth colum ns show the num ber of - tectonic events, a sum of their ener gy releas e cal culate d from their codas, and their fo cal-depth ranges. The next two colum ns descri be the num ber of tremor epi sodes and the asso ci ated en ergy releas e, and the last col umn contains the num ber of long-period events. Courtesy of INGEOMINAS.

Figure 1. A seism ic record of a portion of the Galeras earth quake swarm on 8 July 2004, from the station OLGA on the upper E slope. These were descri bed as frac ture earthquakes. During the record ing process, the seism olo gist on duty adjuste d the dis tance betwee n adja cent traces, setting them farther apart than the up per, com para tivel y quiet portion of the record. The seism olo gist’s notes of earth quake ar rival times appear as faint, poorly legi ble marks on the im age. Severa l earthquakes oc curred at such short inter vals that they over lapped. Courtesy of INGEOMINAS. Volcanism Network, Volume 29, Number 7, July 2004 Galeras 3

Figure 2. Com posite of photos portra ying the active cone at Galeras on 9 July 2004. The photos were taken looking NW. At the time these photos were taken the princi pal focus of emissions was from fumaroles locate d on the W side of the cone. El Pinta crater on the E edge of the main crater was not emitting any visi ble prod ucts; later, how ever, this crater be came the pri mary vent. (A map of crater fea tures ap peared in Bulle tin v. 19, no. 7.) Cour tesy of INGEOMINAS.

On 8 July 2004 a swarm of VT earthquakes was cen- compo nents of the elec tric and mag netic fields at an elec- tered slightly W of the cone at depths of 2-4.5 km. The larg- tro mag netic station at the NE base of the active cone. Since est event had ML 3 (figure 1). The swarm was pre ceded by the be ginning of July, the CO2 sen sor at La Joya fumarole inter vals with LP events and spasm odic tremor at somewhat showed a grad ual de crease in values, and the temper atures lower fre quen cies.. The seis mic ep isode caused tiltmeters to at La Joya and Chavas fumaroles in creased grad u ally just vary on the E and NE flanks During fieldwork on the S and two days before the emission. After 16 July, tem pera ture s at SW sides of the acti ve cone on 9 July, num erous new points Chavas had risen by 20°C and at La Joya by around 5°C. with gas emission were observe d. However, the second ary Accord ing to the person nel of the mil itar y out post at the crater “El Pinta” (at the E edge of the main crater) only pro - summ it of Galeras, gas emissions had in creased by the af - duced sporadi c, weak pulses of gas (figure 2). ter noon of 17 July when com pared with those be fore 9 July. On 9 July, only minor, white-col ored emissions were The emissions came from the El Pinta crater and from observe d. They came from the main crater and from spo- Deformes fumarolic field, which is locat ed ~ 50 m from the radic gas venting from the second ary El Pinta crater. crater on the upper S and SSW flank of the acti ve cone. Gas The first epi sode of ash emissions from El Pinta were emissions subse quentl y decrea sed unti l 20 July, when noted at 0901 on 16 July and was asso ci ate d with tremor. It again, small magni tude earthquakes occurred. took place under condi ti ons of poor vis ibil ity, thwart ing Field obser va ti ons on 19 July disclos ed fresh ash on clear ob ser va tions. At the time of ash emission , tremor with Galeras (fig ure 4). It had vented from El Pinta crater. The very large am pli tudes at the upper-fl ank Olga stati on had ash thickness ranged from 3 mm at the base of the cone to persis ted for slightly more than 10 hours (figure 3). ~ 20 cm near the point of emission. The right-hand photo The seis mic ity and gas vent ing ac com pa nied sig nals on on figure 5 shows field workers ascend ing the steep upper the two tiltmeters, as well as vari a tions in the hor izon tal slopes, walking through the thick ash, leaving deep foot- prints akin to trudging through fresh snow. On 21 July, an ash emission was seen rising to ~ 500 m above the vol cano’s rim (figure 5). It was widely vis i ble, in clud ing from the larg est ad ja cent city, San Juan de Pasto, which lies just to the E. Seis mic sig nals in creased and include d a vari ety of wave forms such as short im pulsive events as well as more com plex ones. Tremor on 21 July was par- tic u larly strong (of ten dom i nat ing the record) and of long dura - tion–extend ing for ~ 13 hours. Once again the elec tric- and mag - netic-field sen sors ap peared to respond to the onset of emissions. Figure 3. A seism ic record from station Olga on 16 July 2004, showing exam ples of the seism ic signals seen as the Although ash-free, gaseous erup tion began. Only a few of the lo cal (or mi cro) earth quakes were in ferred to be as so ci ated with clas sic rock emissions occurred on 23 July, frac ture. The bulk of the record con tains more com plex waveform s, inferr ed to be relate d to fluid movem ent. The ash-bearing ones were noted on bottom of this record is dom inated by the kind of high-am plitude tremor often as soci ated with ac tive venting many days in the fol lowing weeks during this eruptive epi sode. Heavy index lines appear on the seism ic record every minute; lighter (faint) from El Pinta. Spe cif ically, ash in term edi ate lines are 10 seconds apart. Cour tesy of INGEOMINAS. 4 Galeras Smithsonian Institution — Bulletin of the Global

noes. Ma jor ex plo sive erup tions since the mid-Holo cene have pro- duced widesprea d tephra depos it s and pyroclastic flows that swept all but the southern flanks. A cen- tral cone slightly lower than the caldera rim has been the site of nu mer ous his tor i cal erup tions since the time of the Spanish conquistadors. Ref er ences: Bruce, V., 2001, No appar ent danger: the true story of vol canic di sas ter at Galeras and Nevado del Ruiz: Harper Col lins, 239 p. McNutt, S., 2000, Seis mic Figure 4. Galeras recon nais sance inves ti ga tions under taken on 19 July (3 days after the ash emission of 16 July). The left-hand photo shows a team in the vol cano’s E sector where they found thin ash-fall de posits. The mon i tor ing, in En cy clo pe dia of right-hand photo shows climb ers on the upper part of the cone at El Pinta, in vicin ity of the vent, where substan tial Volca noes (H. Sigurdsson, Edi - ash had fallen. Cour tesy of INGEOMINAS. tor-in-chief): Aca dem ic Press, p. 1095-1119. Seidl, D., Calvache, M., Bannert, D., Buttkus, B., Faber, E., Greinwald, S., Hellweg, M., and Rademacher, H., 1998, The Galeras multiparameter-station: Deutsche Geophys. Ges., Sonderband III / 1998 (Herausg.: J. Zschau, M. Westerhaus), p. 9-11. Willi ams, S., and Montaigne, F., 2001, Surviv ing Galeras: Houghton Mifflin, 270 p. In for ma tion Con tacts: Diego Gomez Marti nez, Observatorio Vulcanológico y Sismológico de Pasto (OVSP), INGEOMINAS, Carrera 31, 1807 Parque Infantil, PO Box 1795, Pasto, Colom bia (Email:dgomez@ingeomin. gov.co; URL: http://www.ingeomin.gov.co/pasto/; Email: [email protected]); Wash ing ton Vol ca nic Ash Ad vi- sory Cen ter (VAAC), Sat el lite Anal ysis Branch (SAB), Figure 5. The ash-bearing erup tion from Galeras on 21 July 2004, as seen NOAA/NESDIS E/SP23, NOAA Science Center Room looking W from the town of Pasto. The town sits on the vol cano’s flank, 401, 5200 Auth Rd., Camp Springs, MD 20746 USA mak ing it vul ner a ble to slope in sta bil ity and other vol ca nic haz ards. Pasto (URL: http://www.ssd.noaa.gov/). res i dents have pre vi ously un der gone con sid er able ten sion due to un rest at Galeras in the 1989-2002 eruptive ep isode. Courtesy of INGEOMINAS. plumes were every day during 27-31 July ac com panied by tremor; LP and VT earth quakes were also re corded. Some of these proces ses were heard from canyons around the vol- cano. Sev eral changes at the ac tive cone were noted, which include d increa ses in both vent ing, exit pressures , and quanti ties of gases driving the eruptions. An after noon overfli ght on 28 July con firmed a vigor - ous ash plume com ing from El Pinta crater reaching to ~ 1 km alti tude and visi ble for a distanc e ~ 5 km. A morning overfli ght on 29 July showed a light, gray to off-white col - ored plume again emerging from El Pinta and in this case descri bed as blowing NNW, the prevail ing di recti on of strong wind in this season of the year. On 29 July a low ash plume was visi ble from Pasto. On that day, sci enti sts took a therm al im age of ash clouds; the max i mum tem per a tures were 260°C, seen on the cloud’s E side, at a spot above the vent at El Pinta (figure 6). SO2 measured on 31 July gave a value of 1,366 tons/day. Two non-techni cal books dis cussed the 14 Janu ary 1993 Galeras erupti ons that killed six sci enti sts and three tourist s (Bruce, 2001; Willi ams and Montaigne, 2001). Figure 6. Ther mal im age of a Galeras eruption cloud on 29 July 2004 Back ground. Galeras, a with a large com ing from El Pinta crater (N is to wards the bot tom of this im age). The im age was taken by INGEOMINAS with the sup port of the Air Force of breached cal dera lo cated im medi ately W of the city of Colom bia, from ~ 500 m over El Pinta crater. The right hand side shows Pasto, is one of Colom bia’s most fre quently ac tive volca - the tem per ature scale. Cour tesy of INGEOMINAS. Volcanism Network, Volume 29, Number 7, July 2004 Manam 5

dropped again the week of 12-18 July. Bromo’s emissions Tengger Cal dera conti nued to bear ash, and during 14-27 June a thick ash plume rose 25-100 m above the crater rim. In ac cord with east Java, In do ne sia the de cline in seis mi cally de tected emis sions, ob serv ers 7.94°S, 112.95°E; sum mit elev. 2,329 m noted smaller (25-50 m high), thinner plumes during 28 June-18 July. Mount Bromo’s 8 June 2004 erupti on killed two visi tors Other seis mic ity also de creased (ta ble 2). Seis mom e ters and injured five more (Bul le tin v. 29, no. 5). This re port recorded 15 type-A earthquakes during 21-27 June, but this mainly adds a few detai ls for the events of 8 June and a was a peak in the trend for 14 June-18 July, which was gen - video of the erupti on plume. It also sum mariz es re ports er ally 1-2 per week. Seism ome ters re corded no type-B through 18 July, an inter val charac ter ized by mild ash-bear- earth quakes at Bromo since the week of its phreatic erup- ing erupti ons (to 100 m high) without a repeat of the robust tion. Tremor, conti nu ous during 7-13 June, dropped to 2-3 erupti on seen on 8 June. events/week. Lo cal tec tonic earth quakes were in ter mit tent. A 3-minute- long video clip of the erupti on was shot by Back ground. The 16-km-wide Tengger cal dera is lo- Kiyoshi Nishi, a volcano seis molo gist attac hed to the Indo - cated at the northern end of a volca nic massif extend ing ne sian Di rec tor ate of Vol ca nol ogy and Geo log i cal Haz ard from Semeru vol cano. The massive Tengger volca nic com - Mit i ga tion (DVGHM). (DVGHM was re or ga nized from plex dates back to about 820,000 years ago and consis ts of the form er Volcanological Survey of Indo ne sia ). Nishi five overlap ping stratovolcanoes, each truncat ed by a cal- works for the Ja pan In ter na tional Co op er a tion Agency, a dera. Lava domes, pyroclastic cones, and a maar oc cupy the Jap a nese gov ern ment or ga ni za tion of fer ing tech ni cal and flanks of the massif. The Ngadisari caldera at the NE end of grant as sis tance. the com plex formed about 150,000 years ago and is now The video begins after a substa nti al plume had already drained through the Sapikerep val ley. The most re cent of devel oped. The plume conti nued to rise, and the main body the Tengger calde ras is the 9 x 10 km wide Sandsea caldera of it appeare d to as cend with only minor effect s of wind, at the SW end of the com plex, which formed incrementally ris ing in a roughly ver ti cal di rec tion. Iden ti fi able zones of during the late Pleisto cene and early Holo cene . An overlap - disti nct color ati on appeare d within the plume, in shades of ping cluster of post-caldera cones was construc ted on the brown, reddish-brow n, gray, and white. The white-gray floor of the Sandsea cal dera within the past several thou- zone, which clearly erupted ear lier, moved away from the sand years. The youngest of these is Bromo, one of Java’s viewer. Most of the foot age shows the brown and red parts most acti ve and most frequently visited volcanoes. of the plume evolving. Subsid iar y clouds several times be - In for ma tion Con tacts: Di rec tor ate of Vol ca nol ogy and gan bulging out of the main plume’s margins. The im age is Geo log i cal Haz ard Mit i ga tion (DVGHM), Jalan valu able be cause of the need to accu rately assess ash plume Diponegoro No. 57, Bandung 40122, Indo ne sia (Email: heights and be havior such as the rise time of the plume top, [email protected]; URL: http://www.vsi.dpe.go.id/); Dar- colored zones, and subsid iar y clouds, and the abso lut e win Volc anic Ash Advi sory Cent re (VAAC), Bureau of Me- plume heights with re spect to time. te o rol ogy, North ern Ter ri tory Re gional Of fice, PO Box Seism icit y during 9-14 June was marked by long peri - 40050, Ca suarina , NT 0811, Aus tra lia (URL: http://www. ods of conti nu ous tremor (maxi m um peak-to-peak am pli- bom.gov.au/info/vaac/); Kiyoshi Nishi, Ja pan In ter na tional tude 6.0 mm), shal low type-A and type-B vol canic earth- Co op er a tion Agency (JICA) (URL: http//www.jica.go.jp/). quakes, inter mit tent tec tonic earthquakes , and a high num ber of emission earthquakes (see table 2 and Bul le tin v. 29, no. 5 for detai ls). Reports around this time noted that distanc e meter s (EDM) and global posi ti oning system Manam (GPS) re ceivers on Bromo recorded de form ati on that sug- gested defla tion of the edi fic e. On 14 June, Bromo ejected offshore New Guinea, Pa pua New Guinea another ash plume that rose 100 m above the summit. 4.10°S, 145.06°E; sum mit elev. 1,807 m Nearly two weeks after the 8 June erupti on, no sim ilar ly substa nti al event had occurred. On 15 June, DVGHM de- Ac tiv ity at Manam’s two summit craters re mained low creased the Alert Level to II, or ‘erupti on imminent.’ Re- during July. The sum mit area rem ained mostly cloud-cov- ports cover ing 14 June-18 July noted a decrea se in seism i- ered during the month; however, when the clouds cleared cally detected vol canic emis sions (table 2). The num ber of both craters were re leasing white va por at weak-to-mod er - emission earthquakes decrea sed by ~ 50% after 20 June and ate rates. No seis mic re cord ing was car ried out due to short - age of re cording paper. There was Volca nic Vol ca nic Lo cal no night-time glow observe d dur- Date Tremor Emis sion ing the month. Rem ote sensing Type A Type B Tec tonic sci en tists work ing with the MODIS Therm al Alert System 07 Jun-13 Jun 26 15 con tin u ous 0 387 noted that no new acti vit y was de- 14 Jun-20 Jun 0 0 0 0 376 tected by MODVOLC from 1 21 Jun-27 Jun 15 0 3 3 163 January 2003 to 31 May 2004. 28 Jun-04 Jul 1 0 2 0 104 Back ground. The 05 Jul-11Jul 2 0 2 3 116 10-km-wide island of Manam, ly - 12 Jul-18 Jul 2 0 3 0 79 ing 13 km off the northern coast Table 2. Weekly seism icity at Bromo as measured by the Volcanological Survey of In done sia (VSI) seism ograph. of Papua New Guinea, is one of Courtesy of VSI. the country ’s most acti ve volca - 6 Pago Smithsonian Institution — Bulletin of the Global noes. Four large radial valley s extend from the unvegetated ported during the month. Emission of thin white va por from summit of the con ical ba saltic-andesitic stratovolcano to its the two N-val ley vents was re ported during 4-6 July. Seis- lower flanks. Two sum mit craters are pres ent; both are ac - mic acti vit y was at a low level. Ground de form ati on conti n - tive, al though most his tor i cal erup tions have orig i nated ued to show a steady upli ft that began late last year. from the southern crater, concen tra ting erupti ve products Air Niugini pilot David Innes noted on 23 August that during the past century into the SE ava lanc he val ley. Fre- he had flown past Uluwan early the previous week and quent histor i cal erupti ons have been re corded at Manam noted what appeare d to be steam and light ‘smoke,’ but did since 1616. A major erupti on in 1919 produced pyroclastic not note any ash flows that reached the coast, and in 1957-58 pyroclastic The Darwin Vol canic Ash Advi sory Center posted two flows descended all four radial valleys. Lava flows reached reports on Ulawun. The ini tial 22 August re port noted “thin the sea in 1946-47 and 1958. plume to FL 100 [~ 3 km alti tude] extends 60 NM [~ 110 In for ma tion Con tacts: Ima Itikarai and Herman Patia, km] to SW on NOAA 15 [im age of 2038 UTC on 22 Au- Rabaul Vol cano Obser va tory (RVO), P. O. Box 386, gust] . . .. At 0330 UTC on 23 August ash was not identi fi- Rabaul, Pa pua New Guinea (Email: [email protected]); able from satellite data.” Rob Wright, Luke Flynn, and Eric Pilger, MODIS Therm al Andrew Tupper reporte d that on the morning of 23 Au- Alert Sys tem, Ha waii In sti tute of Geo phys ics and Plan e tol - gust satel li te im agery showed a plume ~ 50 km long es cap- ogy (HIGP), School of Ocean and Earth Science and Tech- ing from Ulawun (figure 7). He went on to com ment that nolog y, Univer sity of Ha waii at Manoa (URL: http://modis. the light at that time and the mete o ro log ical con di tions were hgip.ha waii.edu/; Email: [email protected] .edu, perfect for creat ing and seeing plumes. Discus sion with [email protected] waii.edu, and [email protected] .edu); Da- RVO suggest ed that Ulawun often steams in roughly the vid A. Rothery and Char lotte Saunders, De part ment of same manner, but that atm ospheri c condi ti ons are only Earth Sci ences, The Open Uni versit y, Mil ton Keynes, MK7 someti me advan ta geous for seeing the plume. Tupper noted 6AA, United Kingdom (Email: [email protected]). that “In stagnant and/or unsta ble air, the plume might rise higher above the volcano, but be less visi ble to sat elli tes (and be obscure d by convec ti ve clouds); fresh dry-sea son air flow is by far the best for creating and spotting plumes.” Pago Back ground. The sym met ri cal ba saltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bis- , Papua New Guinea marck arc, and one of Pa pua New Guinea’s most fre quently 5.58°S, 150.52°E; sum mit elev. 742 m acti ve. Ulawun vol cano, also known as the North Son, rises above the north coast of New Britain oppo sit e Bamus vol- Pago was quiet during July. The upper vents re leased cano, the South Son. Satellitic cones oc cupy the NW and thin white vapor throughout the month. No emission was eastern flanks. A steep-walled val ley cuts the NW side of ob served from the lower vents. Seism ic activ ity was at a Ulawun volcano, and a flank lava-flow com plex lies to the low level. south of this valley . His tori cal erupti ons date back to the Back ground. Pago is a young post-caldera cone that be gin ning of the 18th cen tury. Twen ti eth-cen tury erup tions was construc ted within the 5.5 x 7.5 km Witori cal dera. Ex- were mildly explo sive unti l 1967, but after 1970 several ten sive pyroclastic-flow de pos its are as so ci ated with for- larger erupti ons produced lava flows and ba saltic mati on of the cal dera about 3300 years ago. The gently pyroclastic flows, greatly modifying the summit crater. sloping outer flanks of Witori vol cano consis t pri maril y of In for ma tion Con tact: Rabaul Vol cano Ob ser va tory dacitic pyroclastic-flow and airfall depos it s produced dur- (see Manam); Da vid Innes, Air Niugini, PO Box 7186, ing a serie s of five major explo sive erupti ons from about 5600 to 1200 years ago. The post-caldera cone of Witori, Mount Pago, may have formed less than 350 years ago. Pago has grown to a height above that of the Witori cal dera rim. A series of ten dacitic lava flows from Pago cov ers much of the caldera floor. The youngest of these was erupted during 2002-2003 from vents extend ing from the summit nearly to the NW caldera wall. In for ma tion Con tact: Rabaul Vol cano Ob ser va tory (see Manam).

Ulawun New Britain, Papua New Guinea 5.04°S, 151.34°E; sum mit elev. 2,334 m All times are lo cal (= UTC + 10 hours)

Ulawun rem ained quiet during July 2004. Emissions from the main vent consis ted of white vapor being re leased Fig ure 7. NOAA sat ellite im age of plume from Ulawun taken on 22 at moder ate rates. Wisps of blue vapor were reporte d on August. Arrow points to Ulawun; the plume was ~ 50-60 km long. 4-5, 7, and 12-14 July. No noise or night-time glow was re - Courtesy of Andrew Tupper. Volcanism Network, Volume 29, Number 7, July 2004 Yasur 7

Boroko, Port Moresby, Na tional Cap ital Dis trict, Pa pua New Guinea (Email: [email protected] , URL: http:/ Yasur /www.airniugini.com.pg/); An drew Tupper, Darwin Volca - nic Ash Advi sory Centre (VAAC), Com monweal th Bureau Vanuatu, South Pacif ic of Me te o rol ogy, North ern Ter ri tory Re gional Of fice, PO 19.52°S, 169.43°E; sum mit elev. 361 m Box 40050, Casua rina , NT 0811, Aus tra lia (URL: http:// www.bom. gov.au/info/vaac/; Email: dar win.vaac@bom. At the end of June 2004, Yasur volcano started a new gov.au). cy cle of high ac tiv ity, the fifth since con tin u ous mon i tor ing began in 1993. This cycle is expect ed to last several months. Having reached a clim ax in 2002, a lessen ing of acti vit y had been observe d throughout 2003. A re turn of el- Rabaul evate d acti vit y was noted in March 2004, herald ing the cy - cle that began toward the end of June (figure 8). The bulk of New Britain Is land, Papua New Guinea the seis mic record (over 95%) measured by a stati on lo- 4.271°S, 152.203°E; sum mit elev. 688 m cated 2 km from the crated rep re sented ver tical ground-movem ent greater than 60 mm. The increa se-de- Tavurvur conti nued to rem ain quiet dur ing July. Ac tiv - crease cy cle is clearly vis i ble. Un for tu nately, prob lems with ity con sisted of white vapor being re leased in vari able the power supply of the sta tion’s transm it ter inter rupted the amounts throughout the month. Seism icit y was at a low flow of data at the time of onset of high acti vit y. level. Five high-frequency earthquakes occurred each day The new cy cle of high acti vit y that be gan in late June on 17, 19 and 25 July and two events occurred on 27 July. 2004 was ac compa nied by ash ejec tion. Ash fall reached Only three of these earth quakes were lo cated, two NE of sev eral milli me ters in thick ness at dis tances up to 4 km the caldera and the other E of the caldera. Ground defor m a- from the vents. The cy cle was linked to the reopen ing of the tion conti nued as slow upli ft, which began in October 2003. three main channels feeding vents A, B, and C, and the con- Back ground. The low-ly ing Rabaul cal dera on the tip se quent re-emergence of emissions at all three vents. of the Gazelle Pen in sula at the NE end of New Brit ain Fieldwork was conducte d on Tanna Island dur ing 10-15 forms a broad shel tered harbor uti lized by what was the is - July 2004. Vent A exhibited large ash plumes and low-in- land’s largest city prior to a major erupti on in 1994. The tensit y explo sions (figures 9 and 10), with lava bombs outer flanks of the asymm etri cal pyroclastic shield vol cano ejected to ward an area NW of the crater. Strombolian ac tiv - are formed by thick pyroclastic-flow de posit s. The 8 x 14 ity was observe d at vent B (figure 11). This was the most km caldera is widely breached on the east, where its floor is explo sive of the vents, with lava bombs project ed verti cally flooded by Blanche Bay. Three small stratovolcanoes lie more than 300 m above the crater rim. The plume’s bluish outside the northern and NE cal dera rims of Rabaul. color was quite visi ble, confirm ing the pres ence of SO2. A Post-cal dera erup tions built ba saltic-to-dacitic pyroclastic wall of sco ria at vent C, pres ent now for sev eral years, sep a - cones on the cal dera floor near the NE and west ern cal dera rates this vent from vents A and B. Lava ejections from walls. Several of these, includ ing Vul can cone, which was vent C did not extend be yond the lip of the vent. Very dense formed during a large erupti on in 1878, have produced ma- ash plumes were emitted, but their in ten sity decreased af ter jor ex plo sive ac tiv ity dur ing his tor i cal time. A pow er ful ex- 10-11 July. From 11 to 15 July, the scientists measured SO2 plo sive erup tion in 1994 oc curred si mul ta neously from con cen tra tion us ing a Mini Doas spec trom e ter and cal cu- Vulcan and Tavurvur volcanoes and forced the temporary lated a daily out put of SO2 of around 1,000 metric tons per abandonment of Rabaul city. day, twice the amount measured in April 2004. In for ma tion Con tact: Rabaul Vol cano Ob ser va tory Back ground. Yasur, the best-known and most fre- (see Manam). quently visit ed of the Vanuatu vol canoes, has been in

Fig ure 8. Evolu tion of ac tivity seen and measured at Yasur vol cano from 1 Janu ary 2003 to 21 July 2004. The hori zon tal scale uses the conven tion of day, month, and year; the ver tical scale shows upwar d incre asing ‘level 3’ seism icity , which is de fined as ground displace ments of over 12.4 microm eter s (Fm). The his to gram bars were based on seis mic measure ments re corded by a station lo cated 2 km from the crater and trans mit ted via the sat el lites of the Argos system . The text explains vari ous aspects of the data and volca nism . Cour tesy of Michel Lardy and Philipson Bani, IRD. 8 Yasur Smithsonian Institution — Bulletin of the Global

Figure 9. An over view of Yasur’s crater on 11 July 2004. Vents are labeled and show typi cal activ ity seen dur ing the visit. Copyright ed photo cred ited to M. Lardy, IRD.

Figure 11. Yasur’s vents B (in front), showing blueish emissions, as well as vent C (far thest back), emit ting a taller, dense plume. The shot was taken dur ing the fieldwork of 10-15 July 2004. Copy righted photo cred ited to P. Bani, IRD.

contai ned within the small Yenkahe cal dera and is the youngest of a group of Holo cene volca nic center s con- structed over the down-dropped NE flank of the Pleisto cene Tukosmeru vol cano. Ac tive tectonism along the Yenkahe Figure 10. Yasur’s vent A in the midst of a dense emission of bombs and horst accom pany ing erupti ons of Yasur has raised Port Res- ash. A light- colored plume sits over vent C (to the right and in the olu ti on harbor more than 20 m during the past century. background). The shot was taken dur ing the fieldwork of 10-15 July 2004. In for ma tion Con tacts: Michel Lardy and Philipson Copyright ed photo credited to M. Lardy, IRD. Bani, IRD (Institut de Re cherche pour le Développement) UMR Magm as et Volcans, BP A5 98848 Nouméa Cedex, New Cal edo nia (Email: [email protected]; more-or-less conti nu ous strombolian and Vulcanian ac tiv- [email protected]); Jeanne Tabbagh, DGA ity since Captai n Cook observe d ash erupti ons in 1774. (Département de Géophysique Appliquée), Université Paris This style of acti vit y may have conti nued for the past 800 VI, 4 Place Jussieu 75252, Paris Cedex 05, France (Email: years. Yasur, lo cated at the SE tip of Tanna Is land, is a [email protected]), Esline Garaebiti, De part ment of mostly unvegetated 361-m-high pyroclastic cone with a Geol ogy, Mines and Water Resource s (DGMWR), PMB nearly cir cu lar, 400-m-wide sum mit crater. Yasur is largely 01, Port- Vila, Vanuatu (Email: [email protected]).

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