Bul Le Tin of the Global Vol Can Ism Net Work
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Bul le tin 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 erup tive 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 mod erate white va por 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 ing ton, 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 Un ion (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 Galeras Smithsonian Institution — Bulletin of the Global var ied and was larg est in the most re cent 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 earth quakes 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 ep isodes 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 in ter val, on 16 July 2004, a of 4.3 Hz. new erupti ve epi sode be gan. In con trast to the 2004 events, In early 2003, LP sig nals conti nued to be present in the the in ter 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 a tive quiet, ex cept for a small ash emission from a sec- their atyp i cal sig na tures. Their fre quency spec tra showed ond ary 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 sig nals, 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 mon itor 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 n ued to show the param eter s (Seidl and oth ers, 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 Jan u ary 2004, and at both times they were cooler than 2004 Galeras volca nism was at very low lev els, 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 ar eas: Deformes parti cu larly 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. Mag nitudes 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 earth quakes in Pasto. Two on 27 was pre ceded 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 de crease be - ary at 0018. Their respec tive local magni tudes (ML) were 2. gan on 6 June and lasted un til 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 v ity picked Table 1 com pares seism icit y for the first quar ter of 2004 up. The earth quakes exhib it ed high frequen cie s, and they with the last quarter in 2002 and the first in 2003. The num - un derwent rapid atten u ati 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 volcano- 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 leg ible 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 pho tos 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 Bul letin 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 sta tion at the NE base of the ac tive 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 a tures lower fre quen cies.