Bul Le Tin of the Global Vol Can Ism Net Work

Home , Ol Doinyo Lengai

Bul letin of the Global Vol can ism Net work Vol ume 29, Number 2, February 2004

Llaima (Chile) Extre me glacial crevassing and melting; April 2003 ash emis sions ...... 2

Soufriere Hills (Montserrat) Ash to 7 km alti tude on 3 March 2004; pyroclastic flows reached the sea.....5

Kilauea (Ha waii) Activ ity through April 2004 focuse s in upper flow field (maps and dia grams ) ...... 6

Ruapehu (New Zea land) Strategy, predic tion, and man agement of crater-lake over flow and pow erful lahar..8

Langila (Pa pua New Guinea) MODIS ther mal alerts in April 2003, and Janu ary 2004 ...... 9

Rabaul (Pa pua New Guinea) 1-17 Feb ru ary 2004-ash falls 30 km to the E ...... 9

Ulawun (Pa pua New Guinea) Tab u la tion of avi a tion re ports is sued dur ing 2000-mid-2003 ...... 9

Pago (Pa pua New Guinea) Two ex plosions on 24 Febru ary 2004, other wise quiet dur ing that month .....11

Manam (Pa pua New Guinea) One mi nor erup tion but oth er wise low ac tiv ity dur ing Feb ru ary 2004 .....11

Ruang (In do ne sia) Eruption on 25 Septem ber 2002 is the largest in Indo ne sia in many years ...... 11

Stromboli (It aly) After 10 Febru ary 2004, explo sions at upper limit of that typi cally seen...... 12

Erta Ale (Ethi o pia) Febru ary 2004 expe di tion finds molten-s urface d lava lake nearly gone ...... 13

Ol Doinyo Lengai (Tan za nia) During Febru ary 2004, lavas still es cape crater; temper a ture measure ments . 13

Edi tors: Rick Wun der man, Ed ward Venzke, Devra Wex ler, and Gari May berry Vol unteer Staff: Robert An drews, Don Gruber, Jacquelyn Gluck, Dave Charvonia, and Ste phen Bentley

Global Vol canism Program · National Museum of Natu ral His tory, Room E-421 · Washing ton, DC 20560-011 9 · USA Tele phone: (202) 357- 1511 · 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 Llaima Smithsonian Institution — Bulletin of the Global

Seismic ity Tremor frequency Date Llaima (RSAM units) (Hz) cen tral Chile 38.692°S, 71.729°W; sum mit elev. 3,125 m Jan u ary 2002 28 0.9 All times are lo cal (= UTC - 4 hours) June 2002 20 — Sep tem ber 2002 57 1.2 During late 2002 and early 2003 Chilean scien ti sts at De cem ber 2002 99 1.2 (dur ing 18-20 De cem ber) Llaima doc u mented in creases in seis micity, fumarolic out - Mid-Jan u ary 2003 93 — put, a minor erupti on, and pronounced glacia l disrup ti on. For exam ple, on 8 Janu ary 2003 they found that the ice and Late Jan u ary 2003 60 — snow form erly capping the N and S crat ers had com pletely April 2003 92 1-2.2 melted. Larger erupti ons began in April 2003, depos it ing 18-19 April 2003 98 — pyroclastic ma te rial, dis pers ing nu mer ous bal lis tic blocks, Table 1. Seis mic ac tiv ity at Llaima summ arized as RSAM (Real-time and cre at ing sub stan tial plumes. seism ic am plitude) values and princi pal tremor fre quencies . In times of Although this re port covers the time inter val from Janu - rela tive quiet, base line val ues at Llaima are ~ 20 RSAM units and 0.9 Hz. These data were taken from reports by OVDAS-SERNAGEOMIN ary 2002 through most of April 2003, the concern then was (which omitted some time in tervals). that Llaima might erupt with the vigor seen in 1994 (Bul le - tin v. 19, nos. 4 and 5). However, during the 2002-03 report ing in ter val erup tions re mained com par a tively mod est. tem ber 2002. In de scribing April 2003 tremor am pli tude the Ice cov ered, pas sively de gas sing. On 26 Septem ber and OVDAS reports stated that it was about “5-fold larger” than 30 Octo ber 2002, scien ti sts from Chile’s Volca nic Risk at base level. Program and the Volcanologic Obser va tory of the South In Sep tem ber 2002, seis mic in stru ments in cluded two An des (OVDAS) flew over Llaima in re sponse to steady in- per manent sta tions (LLAI and MELI) lo cated re spec tively creases in seis micity and fumarolic ac tiv ity since the end of on Llaima’s S flank and S foot. In Decem ber 2002, there June 2002. On the 26 Septem ber flight they viewed the were two por table seis mic re ceiv ers placed on the E flank at summit with its N (main) crater, and Pichillaima, the Lago Verde, which also recorded unrest . The seis micit y smaller SE-flank cone and its crater. They found only a conti nued to increa se from Decem ber 2002 to mid-Janu ary weak steam plume rising gently from the main crater and 2003 (from ~ 70 to ~ 100 RSAM units). After that, it dim in- at tain ing little ad di tional height. This was in con trast to typ - ished and stabi li zed for about two months. ical previ ous behav ior, which consis ted of puffs that rose Sud den changes. A flight on 8 Janu ary 2003 led sev eral hun dred me ters be fore dis si pat ing. OVDAS to see rem ark able changes since the late 2003 ob - The 26 Septem ber 2002 ae rial obser va ti ons found the serva ti ons (figure 1). First, the dense fumarole emit ted from in ter nal walls of the main crater draped in ice and snow. the main crater was much stronger than the one seen 26 Pichillaima lay be neath a cover of clean ice and snow, and Septem ber 2002 (figure 1, top left). Second, the ice and its crater emitted only a small gas plume. The over all scene snow had com pletely melted from main crater’s in ter nal was of quiet, with minor degas - sing amid frigid condi ti ons. Views of the main crater rim on 30 Octo ber 2002 indi cat ed mi- nor ash on the snow, an irreg u lar , figure-ei ght-shaped hole emit ting gases, and a much larger and opti - cally denser steam plume than on 26 Sep tem ber. Llaima’s cover of ice and snow was more com plete than noted in Octo ber 1998. Thus, by com pari son, in late 2002 vis i- ble signs of ther mal activ ity had di min ished sig nif i cantly. In con- trast to what was typ ically seen, the crater’s ice-cov ered in ter nal walls lacked es cap ing gases. Ex- cept for seis micity, the ice-bound Llaima seemed stable. Seis mi cally rest less. De spite the lack of visi ble vol canism or ther mal ac tiv ity, the seis mic ity in Sep tem ber 2002 was no ta bly greater than in Janu ary 2002 (ta- Figure 1. Contra sting views of Llaima’s sum mit crater and Pichillaima as seen on 26 Septem ber 2002 (left, top ble 1). The frequency of tremor and bottom , re spectivel y) com pared to 8 Janu ary 2003 (right, top and bottom , re spectivel y). The scenes highlight increa sed from 0.9 Hz in Janu ary dif fering condi tions, partic u lar ly the melting of ice and snow. On 26 Septem ber 2002 snow covere d most of the 2002 (a typi cal value in times of ed i fice. On 8 Jan u ary 2003 there was an ab sence of sig nif i cant ice and snow from parts of the crater walls, rim, rel ati ve quiet) to 1.2 Hz in Sep- and S flanks, and there were in creased emis sions of vol canic gases. Cour tesy of OVDAS-SERNAGEOMIN. Volcanism Network, Volume 29, Number 2, February 2004 Llaima 3 walls. Third, com plete melt ing of ice and snow had left ex- snow at Pichillaima had re ceded by 1.0-1.5 km from its top- posed rock at both the sum mit and Pichillaima (figure 1, ographi c high. Ice margins appeare d sub-verti cal and lower right). Fourth, num erous new crevasse s had appeare d en gulfed circular melt areas. in the cone’s gla ciers, parti cu lar ly on the E flank. Down all Other amazing photos taken 11 April 2003 re vealed flanks of the volcano, the 8 Janu ary observ ers saw ice falls, dram atic changes in glacie rs and snow fields (figure 3). snow av alanches, ice detach ments, and rockfalls. Many regions of the ice appeare d to be in moti on and un- Although the melt ing came at the time of the annual der go ing acute me chan i cal fail ure. Nu mer ous pro found thaw, the sit ua ti on on the vol cano indi cat ed that proces ses crevasse s had emerged, includ ing sets of broadly trans- such as lo cal heat ing ac celer ated the melting. Snow had verse, ar cu ate cre vasses trending from glacial mar gins and fallen in early Oc tober 2002. The absenc e of ice and snow ex tend ing well into their axial areas. cover on both the shaded and unshade d sides of Llaima was On 12-13 April 2003 the main crater issued intens e cited as ev i dence in di cat ing el e vated rock tem per a ture. Ob - pulsing fumarolic de gassing at 1- to 3-minute inter vals. servers saw the melt ing and also noted a halt to any new ac - Odors and celeste color were again in dic ative of SO2 and cum ula ti on of ice and snow depos it s. The melt ing was at- HCl com ponents ; such emissions were noted unti l 1500 on tributed to magma at depth in the conduit , and consid er able 13 April. Other proces ses on those days include d mass heat emerging at the lo cations where the ice melted. wast ing, some times with as so ci ated dust, ap par ent vi bra- The re port issued 20 Janu ary 2003 noted that field work tions at the summit, and bal lis tic dis charges from the main on Llaima’s W side (Cherquenco-El Salto) had disclos ed crater. At 1310 on 13 April, expul sions inten si fie d and oc- deep new cre vasses in the gla cial ice reach ing 1.5 km long. curred at 1 minute intervals. Plumes blew E. These were af fili ated with avalanching from near the main Con tin ued ob ser va tions re sulted in the rec om men da tion cone’s sum mit to the cone’s NW foot (~ 3 km long by 0.5 to main tain the Yel low sta tus at least through 16 April as km wide). Observ ers also noti ced conti nued signs of thaw- erup tions be gan to con tain sig nif i cant tephra. Vol ca nol o- ing, includ ing the appear ance of small fumaroles, which gists ex pressed con cern that the vol cano’s gla cial ice-cover they again attri buted to the volcano warming. could undergo further melt ing, which might lead to large The next avail able reports, from the pe riod 9-11 April, and sudden outbursts of water (gla cier bursts) traveling came from eye-wit nesses. Rodrigo Marín of Conguillío na- down local drainages. tional park, noted “an increa se of fumarole ac tivit y in the On 16 April at 1453 OVDAS person nel in the Lago main crater between 9 and 10 April, which was ac compa - Verde area confirm ed gas eous emissions were conti nu ing nied by ash emission.” In addi ti on, from the N slope to es cape from the crater. They re ported that at 1535 these (Captrén) people heard under ground noises. emissions inten si fie d and reached 200 m above the crater At 1330 on 10 April a teacher at Los Andes de Melipeuco ele m entar y school noted three ash explo sions that reached ~ 500 m above the main crater and disperse d NE. Sev eral others observ ers noted ash-bearing emissions from the main crater, includ ing one at 1340 and another at 1350. A park ranger noted that around 2100-2200 on 10 April strong and conti nu ous explo sions awoke him and ash began to fall on him in the N-slope sector of Captrén. Later, the explo sions becam e more sporadi c, and he heard sounds sim ilar to those made by the moti on of heavy machin ery . This conti nued into the early morning of 11 April. The di rector of the above-menti oned school re ported to OVDAS that on 11 April at 0915 he saw “...conti nu ing ash emission from the main crater.” Finall y, at 1100 on 11 April, OVDAS ob serva tory (Cerro Ñielol-Temuco) staff observe d a verti cal colum n, mainly of vol canic gases, which rose to about 600-700 m above the crater rim. This fed a large, hori zon tal , lenti cu lar cloud ~ 30 km in di am eter , the top of which rose to about 3,900 m altitude. An 11 April heli copter flight disclos ed a thin layer of pyroclastic mate rial spread widely across the gla ciers on the NE, E, SE, and SW flanks, visi ble out to distanc es of ~ 4 km. Im pact crat ers in the ice testi fied to num erous bouncing and rolling projec ti les. Sci enti sts on that flight noted vigor - ous fumarolic acti vit y and dense clouds with colors and odors indi cat ing the pres ence of SO2 and HCl. At multi ple spots, small fumaroles had sprouted from the crater walls. The crater floor con tained a 50-m-diam eter vent emitting gases, but no lava flows had emerged. Although the 9-11-April erupti ons were modest , they prompted Llaima’s Figure 2. Two vistas of Llaima on 11 April 2003 docu menting the rapid ice haz ard status to rise from Green to Yellow. reces sion and melt ing around the main crater and Pichillaima. (A) Rim Figure 2 portra ys fur ther melt ing and expo sure of un- and flanks of the sum mit and asso ci ated main crater standing with large derly ing rock at both the sum mit (top) and Pichillaima areas ice free. (B) Pichillaima, nearly ice free and en circled by thick ice at (bottom) on 11 April. When photo graphed, the ice and the limit of ice melting. Cour tesy of OVDAS-SERNAGEOMIN. 4 Llaima Smithsonian Institution — Bulletin of the Global

the crater. The per sons who stayed (me included) re alized that there was an in cred ible warm feel ing while laying on the ground. This was due to the amount of va por with some faint smell of sulphur. We could even take off our jackets and shirts, as long as we were lay ing flat. Af ter lying for a while it was even too hot to [conti nue]. Fantas tic feeling, lying al most on top of the volcano, with a tremendous view, feeling the warmth through the rocks.” Thus, on 18 April, Bataille and students affirm ed the previ - ously stated idea of heat emerging to cause the melt ing and leading to the sudden emergence of cre- vasses ob served since De cem ber Figure 3. Four views of Llaima from heli cop ter , taken on 11 April 2003 showing newly exposed rock surfaces , 2002. A later clar i fi ca tion from newly cre ated ice-mar gins, and un sta ble, rap idly break ing gla ciers. Llaima’s com par a tively tem per ate late-2002 Bataille on the mode of heat to early-2003 erup tive phase cor related with these re mark able changes in its al pine gla ciers. Cour tesy of OVDAS-SERNAGEOMIN. trans fer (viz., “con duc tive heating,” passed through the rocks; or rim, with the plume blow ing SE and being visi ble for ~ 8 “convec ti ve heating,” transporte d by warmed fluids such as km. They noted that at 1537 gas eous emissions escape d at gases) result ed in this statem ent: “I’m not convince d of Pichillaima. On the N (Captrén) side of the mountai n at ‘con duc tive heat ing’ as a di rect source for the ice melt ing, 1704 the observ ers saw gray-col ored fumaroles. During becaus e of the large amount of gases through the sys tem. 1130-1355 on 17 April from a point near the Lago Verde I’m in clined in stead, to be lieve that melting of the ice is they per ceived SO2 and HCl; they wit nessed gas emission s sim ply due to the large amount of va por flowing through to the NE reaching 200 m above the crater rim and spawn- the loose rocks. How ever, I agree that [these] gases have to ing a plume visible for ~ 10 km. be produced while in contac t with hot mate ria l, and in this The 20 and 23 April 2003 OVDAS reports discusse d sense [could] be affect ed by ‘conduc ti ve heating.’ ” poor vis i bil ity but the per ma nent sta tions in di cated Thus, Bataille observe d that the rocks in the ice-melt high-am pli tude tremor and con sid er able seis mic ity (eg., 98 zone around the sum mit were warm to the touch. He con- RSAM units on 18 and 19 April). OVDAS staff inter preted cluded that they were heated by deeper sources and water these signals as due to fluids and gases moving in inter nal vapor transporte d the heat to the surface . conduit s. They also pointed out the absenc e of high- and The scien ti sts discusse d their result s in a subse quent low-fre quency earthquake swarms, signals that gener all y confer ence paper (Bataille and others, 2003) and on their precede emissions of ash. Small swarms of long-pe riod website, high lighting the seis mic and GPS sta tions in stalled earthquakes began, however, on 25 April. on Llaima’s W and N sides. The for mer seis mic station, Ascent during mid-April 2003. In mid-April 2003 near the Refuge Tucapel, began oper at ing on 17-18 April. Klaus Bataille (a phys i cist and seis molo gist teach ing geo- The latter seis mic station , near Captrén, began operating on physics at the Uni versit y of Concepción) and his students 19-20 April. conducte d field work on Llaima. Amid an inter val of seis- Their record ings lacked earthquakes that could be mic and volca nic quiet on 18 April they ascende d into the linked to deeper sources (no fracture s nor seismo-tectoni c region of ice melt near the sum mit region, and made di rect events) during the period be tween April and the follow ing 4 obser va ti ons rel evant to the issue of heat transport. Bataille months. The whole period was dom inate d by a sequence of made the following comments. tremor s due to the ac tiv ity as so ci ated with the crater. “A week after the explo sion announced by the OVDAS, Tremor en ergy de cayed grad u ally in time. The fre quen cies we (8 students and mysel f) went to insta ll two broadband involved were gener all y stable, though pecu li ar and with- seis mic station s to study the evo lu tion of its ac tiv ity, and out a good model for their genesis. we in stalled a GPS re ceiver as well. When we fin ished with Back ground. Llaima, one of Chile’s largest and most the in stalla tion, it was a clear day and we decided to climb ac tive vol ca noes, con tains two his tor i cally ac tive crat ers, as much as we could. We began early in the morning [of 18 one at the summit and the other, Pichillaima, to the SE. The April] . . . [and] could see from the distanc e fumaroles com - massive 3,125-m-high stratovolcano has a volum e of 400 ing from the crater, and several vents with vapor and gases cu bic ki lo me ters. A Ho lo cene ed i fice built pri mar ily of ac - com ing out from differ ent places, some 200-300 m below cum ulat ed lava flows was construc ted over an 8-km-wide the crater, towards the N. We did not find any im pedi m ent cal dera that formed about 13,200 years ago, follow ing the to con tinue climb ing, nei ther phys i cal dif fi cul ties nor erupti on of the 24 cubic ki lom eter s Curacautín Ignimbrite. anom alous acti vit y from the crater. Thus the whole group More than 40 scoria cones dot the volcano’s flanks. Fol- conti nued up to 300 m below the crater, where four persons lowing the end of an explo sive stage about 7,200 years ago, stayed due to physi cal condi ti ons, and five conti nued up to con struc tion of the pres ent ed i fice be gan, char ac ter ized by Volcanism Network, Volume 29, Number 2, February 2004 Soufrière Hills 5 strombolian, hawai ian, and infre quent subplinian erupti ons. ued unti l af ter noon on 3 March, when, at around 1444, seis- Fre quent mod er ate ex plo sive erup tions with oc ca sional micit y greatly increa sed and an explo sion and collaps e lava flows have been recorded since the 17th century . event occurred. Accord ing to reports from the Montserrat Ref er ence: Bataille, K., Hermosilla, G., and Mora, D., Volcano Obser va tory (MVO) this was the most signif i cant 2003, (ti tle trans lated from Span ish) Seis mic activ ity of event since the collapse event of 12-13 July 2003. Llaima volcano: Dom inate d by phreatomagmatic sources?, The event on 3 March 2004 produced ash clouds that 10th Chil ean Geo log i cal Con gress (10° Congreso reached al ti tudes of about 7 km above sea level, and Geológico), ses sion 5, paper 63, (Oc tober 2003, pyroclastic flows were observe d in the Tar River, with at Universidad de Concepción) (also cited in Revista least two in ci dents of flows reach ing the sea. Seis micity re - geológica de Chile; ISSN 0716-0208) turned to close to background levels by 1525, but vigor ous In for ma tion Con tacts: Hugo Alberto Moreno Roa, ash vent ing con tin ued un til the fol low ing morn ing. Gustavo Alejandro Fuentealba Cifuentes, Paola Andrea Low-level tremor accom panied by hybrid earthquakes con- Peña Salazar, Erwin Edinson Medel Segura, Pedro Jorge tinued for the next 18 hours, includ ing a serie s of hybrid Ortiz Hernandez, Beatriz Eliana Alarcón Avedaño, Chile earthquakes during the evening of 3 March. Observatorio Volcanológico de los Andes del Sur-Servivio Visual obser va ti ons first suggest ed that the 3 March ex- Nacional de Geologia y Mineria (Chile Volcanologic Ob- plosion re moved the small dome that had grown in the col - serva tory of the South Andes—N ati onal Service of Geol - lapse scar in late July 2003. Photo graphs taken on 28 Feb- ogy and Mining) (OVDAS-SERNAGEOMIN), Manantial ruary and 5 March showed the 3 March collaps e to have 1710-Carmino del Alba, Temuco, Chile (URL: http://www. also rem oved part of the NW dome rem nant origi nall y built sernageomin.cl/; Email: [email protected]); Servicio up during 1995-1998. Nacional de Geología e Minería (SERNAGEOMIN), Av. Af ter 3 March, ac tiv ity rem ained el evated for sev eral Santa María 0104, Casilla 10465, Santi ago, Chile (URL: days. A period of low-level tremor occurred on 4 March, http://www.sernageomin.cl/); Klaus Bataille, begin ning at around 1300 and last ing three hours. On 5 Departamento Ciencias de la Tierra, Universidad de March a small explo sion was recorded at 1009, fol lowed by Concepción, Víctor Lam as 1290, Casilla 160-C, a period of ash vent ing. Betwee n 5 and 12 March acti vit y Concepción, Chile (URL: http://red.sismos.udec.cl/llaima/; returne d to lower levels , with 1 LP and 15 hy brid earth- Email: [email protected]). quakes recorded. On 10 March, however, there was a short (10-20 minutes ) period of ele vate d seism icit y early in the morning; later in the day fresh pyroclastic-flow depos it s Soufrière Hills were ob served in the up per reaches of the Tar River Valley. During the second half of the week, short epi sodes of ash Montserrat, West In dies and steam venting were peri od i cal ly observe d, and ash 16.72°N, 62.18°W; sum mit elev. 915 m fallout occurred as far N as St. Georges Hill. All times are lo cal (= UTC - 4 hours) On 15 March, the Washing ton VAAC reporte d a plume of ash extend ing to the W from the sum mit. The fol lowing The Soufrière Hills volcano was quiet for the last few day MVO reporte d a plume extend ing 250 km (135 nauti cal months of 2003, follow ing ac tivit y in May and July that in - miles) W of the volcano. SO2 emis sions fluc tu ated dur ing cluded signif i cant dome growth (Bul le tin v. 28, nos. 10 and Febru ary and the first two weeks of March, peaking at 1017 12). Light ash-vent ing had last occurred during a pe riod of t/d on 1 Febru ary and 1250 t/d on 9 March (table 2). low-am pli tude tremor 3-8 Octo ber. A seism ic event in A beauti fully illus tra ted look at the erupti on from 1995 mid-Janu ary 2004 and a pe riod of tremor and mudflow ac- to present is now avail able (Kokelaar, 2002; Druit t and tivit y in late Feb ruary 2004 were fol lowed by re newed Kokellar, 2002). erupti ve activity on 3 March 2004. Betwee n 1 Octo ber and 18 De cem ber 2003 no dome growth was observe d, and only a few earthquakes per week Date (2003-2004) SO2 emis sions (met ric tons/day) were re corded. Begin ning 18 De cem ber 2003, SO2 emissions increa sed markedly from the previ ous month’s aver - 05 Dec-11 De c 300-900 age of 500 tons/day (t/d), reaching 3,600 t/d (see ta ble 2). 12 Dec-18 De c 500-3,600 On 18 Janu ary 2004, a swarm of low-am pli tude long-pe- 19 Dec-25 De c — riod (LP) earthquakes began, with ~ 1,000 sepa rat e events 26 Dec-01 Jan 500 over an inter val of 36 hours. Fewer than 40 of these earth - 02 Jan-08 Jan 300 quakes trig gered the au to matic seis mic-de tec tion sys tems. 09 Jan-15 Jan 200-590 Another swarm occurred on 30 Janu ary , this time lasting 16 Jan-22 Jan 440 on 22 Janu ary about 30 hours. Again, instru m ents recorded ~ 1,000 sepa - (equip ment servic ing on other days) rate events; these, how ever, were much weaker and only 23 Jan-29 Jan 500-700 four triggered the detection systems. 30 Jan-05 Feb 439-1017 A period of low-level tremor, consis ting of many small 06 Feb-12 Feb 350-450 LP earthquakes , lasted for about 36 hours begin ning 21 13 Feb-19 Feb 350-650 Febru ary . On 24 Febru ary heavy rainfal l (10 mm in 2.5 20 Feb-26 Feb 496-920 hours) result ed in mudflow acti vit y in the Belham valley ; 27 Feb-04 Mar 480-820 signs of mudflows were also observe d in Plymouth. 05 Mar-12 Mar 340-1250

Begin ning the week of 27 Febru ary , acti vit y increa sed Table 2. Sum mary of SO2 emissions recorde d at Soufrière Hills, 5 signif i cant ly. On 2 March, a period of low-level tremor in- Decem ber 2003 to 12 March 2004, using an ar ray of three scanning UV cluded some small hybrid earth quakes. The tremor conti n - spec trom e ters. Cour tesy of Montserrat Vol cano Ob ser va tory. 6 Kilauea Smithsonian Institution — Bulletin of the Global

Back ground. The com plex andesitic Soufrière Hills ter val ob serv ers noted in can des cence and sur face lava volcano oc cupies the southern half of the island of flows at Kilauea’s up per flow field. In gen eral, sur face lava Montserrat. The sum mit area con sists pri marily of a se ries flows were not seen on the coastal flat or Pulama pali. Var i- of lava domes emplaced along an ESE-trending zone. Prior ous vents within Puù Òò were acti ve, and new lava flows to 1995, the youngest dome was Cas tle Peak, which was lo - cov ered parts of the crater floor. Seism icity at Kilauea has cated in Eng lish’s Crater, a 1-km-wide crater breached gen er ally included a few small earthquak es re corded at the widely to the east. Block-and-ash flow and surge de posit s volcano’s sum mit, along with steady weak tremor. Tremor asso ci ate d with dome growth predom inate in flank depos - occurred continuously at moderate levels at Puù Òò. its. Non-erup tive seis mic swarms oc curred at 30-year in ter - During 0550 to 0830 on 18 Janu ary 2004, a large pe riod vals in the 20th century , but with the excep ti on of a of tilt occurred at Kilauea’s Puù Òò cone, amounting to 17th-cen tury erup tion, no his tor i cal erup tions were re- 18.1 microradians of net defla tion. During this pe riod a fis- corded on Montserrat unti l 1995. Long-term small-to-mod - sure opened at the SE base of Puù Òò, trending approx i - erate ash erupti ons begin ning in that year were accom pa- mately radial to the cone. Lava was emitted from the fis sure nied by lava dome growth and pyroclastic flows that forced and from three to four vents nearby. The ini tial flow evac ua ti on of the southern half of the island and ulti mately reached about 1.5 km S of the cone. The S side of Puù destroy ed the capi tal city of Plym outh, causing major socia l Òò was cut by many new frac tures. The lon gest frac ture and econom ic disrup ti on to the is land. consti tuted the N boundary of a shallow graben (a linear Ref er ences: Kokelaar, B.P., 2002, Set ting, chro nol ogy and conse quence s of the erupti on of Soufrière Hills Vol cano, Montserrat (1995-1999), in Dru- itt, T.H. and Kokelaar, B.P., eds., 2002: The erupti on of the Soufrière Hills Vol cano, Montserrat from 1995 to 1999. Geo log i cal So ci ety Lon don, Mem oir No. 21, p. 1-43. Druit t, T.H. and Kokelaar, B. P., eds., 2002: The erupti on of the Soufrière Hills Vol cano, Montserrat from 1995 to 1999. Geo log i cal So ci ety Lon don. In for ma tion Con tacts: Montserrat Vol cano Ob ser va tory, Fleming , Montserrat, West In dies (URL: http://www.mvo.ms/); Wash ing ton Vol ca nic Ash Ad visory Cen ter (VAAC), Sat el lite Analy sis Branch (SAB), NOAA/ NESDIS E/SP23, NOAA Sci ence Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov).

Kilauea Ha waii, USA 19.425 N, 155.292 W sum mit elev. 1,222 m All times are lo cal (= UTC - 10 hours)

Kilauea conti nued to be acti ve Figure 4. A map and cross-sectional dia gram illus tra ting the island of Ha waii (the ‘Big Island, ’ the larg est and at Puù Òò during De cem ber southern m ost in the Hawai ian chain) show ing select ed volcanological feature s and some local ge og raphy . The 2003 through early March 2004. inset shows how the island of Ha waii consists of five volca noes (old to young): Kohala, Hualalai, Mauna Kea, Figure 4 shows sim pli fied maps Mauna Loa, and Kilauea. The larger map em pha sizes Kilauea’s fea tures. Kilauea is cut by two rift zones, the SW and a di a gram matic cross-sec tion and E rift zones. The east rift zone ex tends 55 km from the sum mit caldera to the eastern tip of the Island of Hawaii . The E rift zone con tains a string of craters, includ ing Puù Òò. The cross-sec tional di a gram dis plays a on the Island of Hawaii , em pha- sim plified model of Kilauea’s inter nal structure . Note the loca tion of vents, at Puù Òò and else where, along the siz ing lo cal ge og ra phy, and SW rift zone. The dia gram also shows a lava tube run ning from Puù Òò to the sea. The map and dia gram both known and inferred condi ti ons at omit the de tails of recent erup tive events; for that, see later fig ures. Courtesy of the Ha wai ian Vol cano Kilauea. During the report ing in- Ob ser va tory, U.S. Geo log i cal Sur vey. Volcanism Network, Volume 29, Number 2, February 2004 Kilauea 7 trough bounded by faults) that was ~ 75 m long and up to 1 sion rate since the Mother’s Day event in May 2002. Dur- m deep. Sur face lava flows were emitted from the E end of ing the report pe riod, weak tremor occurred at Kilauea’s the graben, at the base of Puù Òò. The area S of Puù sum mit along with a few long-period earthquakes . Tremor Òò cone appeare d to be quite unsta ble, so Hawai ian Vol- at Puù Òò rem ained moder ate . During much of Febru ary cano Obser va tory (HVO) sci enti sts warned that no one 2004 and into early March, lava flows and incan des cenc e should ven ture into the area. Seis micity at Kilauea’s sum- were sometim es vis ible in Puù` Oò’s crater and at the mit during 15-20 Janu ary was at low lev els, while tremor at Puù Òò was conti nu ous and at mod - er ate lev els. The tremor picked up during the form ati on of the graben on 18 Janu ary . As of 20 Jan u ary tilt con tin ued to steadily decline following the 18 January deflation event. On 22 Janu ary lava was emitted from the vent formed on 19 Janu ary . The vent and lava flow S of Puù Òò cone were named MLK in honor of the acti vit y that began on the Ameri can civil rights leader M.L. King Jr.’s birthday (19 Janu ary ; see figures 5 and 6). A term that has come into comm on use at Kilauea is “rootless shield.” Lo cal ge ol o gists de- fine this as a pile of lava flows built over a lava tube rather than over a conduit feeding magma from within the Earth. Root less Figure 5. A sketch map showing Kilauea’s lava flows erupted dur ing 1983-23 Jan u ary 2004 activ ity of Puù Òò shields along the tube sys tem and Kupaianaha. Lava flows began erupting from new MLK vent at the base of Puù Òò (star) on 18 Janu ary com monly have flat tops contai n - 2004. Stars in di cate cen ters of re cently ac tive, or still ac tive, root less shields in Mother’s Day flow. New shields ing shallow lava ponds. In the re- form of ten and not all shields appear on this map. Cour tesy of the Ha waiian Volcano Obser va tory , U.S. Geo log i cal Sur vey. porting inter val, there were also sur face lava flows at the W side of the rootless shield called Amal- gamated Bend, a fea ture lo cated SW of Puù Òò (fig ure 6). By 26 Janu ary there were no surface lava flows at the MLK vent, and in can des cence was only vis i ble at the S part of the rootles s shield com plex. On 23 Janu ary moder - ate-to-strong tremor stopped be- neath Kilauea’s cal dera and less- ened at Puù Òò. On 26 Janu ary defla tion that began on 18 Janu - ary ended at Puù Òò after reaching 24.7 microradians. This was proba bly the largest deflation event since early 1997. During 29 Janu ary to 1 Febru - ary mild vol ca nic ac tiv ity occurred at Kilauea, with in can des - cence vis ible at vents in Puù Òò’s crater and small surface flows on the centra l or southern part of the rootles s shield complex. Starting on 18 Janu ary , when the MLK vent formed, the Figure 6. Sketch map of Puù Òò region through 26 Janu ary 2004 identi fy ing num erous vents, groups of lava dis tance across the summ it cal- flows, and other feature s referr ed to in this and previ ous issues of the Bul le tin. Note the names assigned to dera de creased sig nif i cantly, end - intra-crater vents in the oval-shaped in terior of Puù Òò cone (stars 1-7) and the var ious rootless shields farther ing a pe riod of increa sing exten - to the W. Cour tesy of Ha waii Vol cano Ob ser va tory, U. S. Geo log i cal Sur vey. 8 Ruapehu Smithsonian Institution — Bulletin of the Global rootles s shield com plex (an area ~ 0.5 km SW of Puù Òò). Weak background tremor occurred at Kilauea’s summ it along with a few long-period earthquakes. Tremor at Puù Òò was at mod er ate-to-low lev els. Small defla tion and inflation events occurred at the summit and at Puù Òò. Back ground. Kilauea shield volcano, which overlaps the east flank of the massive Mauna Loa shield vol cano, has been Hawaii ’s most acti ve volcano during histor - ical time. Erup tions of Kilauea are prom i nent in Poly ne sian leg ends; writ ten doc u men ta tion ex tend ing back to only 1820 records frequent sum mit and flank lava flow erupti ons that were inter spersed with peri ods of long-term lava lake ac tiv ity that lasted un til 1924 at Halemaumau crater, within the Figure 7. This publicl y dis trib uted im age was cre ated in response to the threat of lahars descend ing the sum mit cal dera. The 3 x 5 km cal - Whangaehu Valley at Ruapehu in 2004. In addi tion to lo cal ge ogra phy , it shows the loca tion of warning sensors, key bridges, and a criti cal em bankm ent (“bund”) to di rect the lahars. The asso ci ated infor m ation discusses dera was formed in sev eral stages warn ings of im pending lahars on the order of 1-2 hours before they ar rive at criti cal downstre am sites. Cour tesy about 1,500 years ago and during of the New Zealand De part ment of Con ser va tion. the 18th century ; erupti ons have also origi nate d from the lengthy East and SW rift zones, Ruapehu was re filling af ter it was empti ed by erupti ons in which extend to the sea on both sides of the volcano. About 1995 and 1996. This lake lies over the main acti ve vent of 90% of Kilauea ’s sur face is formed of ba saltic lava flows the vol cano. Before the erupti ons, the level of the crater less than about 1,100 years old; 70% of the vol cano’s sur- lake was con trolled by an out let that drained wa ter across a face is younger than 600 years. A long-term erupti on from sill of lava into the head of the Whangaehu Valley . During the East rift zone that be gan in 1983 has produced lava the 1995-96 erupti ons, this out let was blocked by 7 m of flows cover ing more than 100 square ki lom eter s, destroy - tephra (fine ash par ticles and other larger mate ri als ejected ing nearly 200 houses and adding new coastline to the by the volcano). island. The De part ment also noted that since March 1999, the In for ma tion Con tact: Ha wai ian Vol cano Ob ser va tory crater lake had risen 52 m and was filling at a rate of 5,300 (HVO), U.S. Geo log i cal Sur vey, Ha waii Vol ca noes Na- m3 per day. On 15 March 2004 the lake’s surface ele va ti on tional Park, P.O. Box 51, Hilo, HI 96718, USA (URL: was re ported at 2,527.6 m above sea level. In mid-March http://hvo.wr.usgs.gov/; Email: [email protected]. 2004 the Depart ment also re ported that the lake was then usgs.gov). ~ 96% full, a point ~ 2 m below the base of the tephra dam emplaced by the 1995-6 erupti ons (the old over flow point). The pre dicted time for the lake to completely fill was given Ruapehu as early April 2004 to Novem ber 2004. An esti mated 60 lahars have swept down the mountai n’s southern side North Island, New Zealand through the Whangaehu Val ley in the past 150 years. A 39.28S, 175.57E; sum mit elev. 2,797 m lahar in 1953 killed 151 people at Tangiwai. The Depart - ment of Con ser va tion re ported ad di tional de tails re gard ing Citing risks about a lahar expect ed when an ash dam the crater lake: there was low to nor mal hy dro ther mal activ - surround ing Ruapehu’s crater col lapses, the New Zealand ity; the water tem pera ture on 15 March 2004 was 35°C; and gov ern ment de cided that drain ing, sluic ing, or si phon ing the lake color was gray. the vol cano’s crater lake to re duce the dan ger was too haz - Back ground. Ruapehu, one of New Zea land’s most ac- ardous, reporte d Jo-Ma rie Brown in The New Zealand tive volca noes, is a com plex stratovolcano construc ted dur - Times (10, 17, and 19 March 2004). The arti cles noted that, ing at least 4 cone-building epi sodes dating back to about in stead, the gov ern ment de cided to bol ster ex ten sive safety 200,000 years ago. The 110 km3 dom inantl y andesitic vol- measures already in place around the volcano, includ ing canic massif is elon gated in a NNE-SSW direc tion and is im proving alarm sys tems. These new measures should pro- surrounded by another 100 km3 ring plain of volcaniclastic vide warnings of lahar oc currence s at least an hour and a de bris, in clud ing the Murimoto de bris-av a lanche de posit on half in advance . The govern m ent also elected to strengthen the NW flank. A serie s of subplinian erupti ons took place at bridges and build an embankment to withstand lahars. Ruapehu betwee n about 22,600 and 10,000 years ago, but The New Zea land Depart ment of Conser va ti on has an pyroclastic flows have been infre quent at Ruapehu. A sin- ex ten sive outreach to discuss the crater lake-lahar prob lem gle his tor i cally ac tive vent, Crater Lake, is lo cated in the (figure 7). They point out that the crater lake on Mt. broad sum mit region, but at least five other vents on the Volcanism Network, Volume 29, Number 2, February 2004 Ulawun 9 sum mit and flank have been acti ve during the Holo cene . rose 1000-2000 m above the sum mit before being blown to Fre quent mild-to-mod er ate ex plo sive erup tions have oc- the E and NE re sult ing in ashfall in the Duke of York curred in his tor ical time from the Crater Lake vent, and islands, ~ 30 km E of Rabaul. tephra char acter istics sug gest that the crater lake may have A slight change in wind di recti on result ed in fine ashfall formed as early as 3000 years ago. Lahars produced by over Rabaul Town and village s downwind on 6 and 13-15 phreatic erup tions from the sum mit crater lake are a hazard Feb ru ary. Oc ca sional weak roar ing noises ac com pa nied to a ski area on the upper flanks and to lower river valleys. some of the explo sions on 5 and 11 Febru ary . From 18 Feb- In for ma tion Con tacts: The New Zealand Herald, PO ruary unti l the month’s end, Tavurvur was only re leasing Box 32, Auckland, New Zealand (URL: http://www. weak white va por, with occa siona l blue vapor. nzherald.co.nz/); New Zea land De part ment of Con ser va- Seis mic activ ity between 1 and 17 Feb ru ary re flected tion, Private Bag, Turangi, New Zea land (URL: http:// the ash emissions at the sum mit. One high frequency event www.doc.govt.nz/); In sti tute of Geo log i cal & Nu clear Sci - occurred on 5 Febru ary , locat ed NE of the caldera. Ground ences (IGNS), Pri vate Bag 2000, Wairakei, New Zea land de for ma tion in di cated a de fla tion ary trend. The real-time (URL: http://www.gns/cri.nz/). GPS and elec tronic tilt site on Matupit Is land, in the cen ter of the cal dera, showed a defla tionary trend since the middle of the month. Langila Back ground: The low-ly ing Rabaul cal dera on the tip of the Gazelle Pen in sula at the NE end of New Brit ain New Britain Is land, Papua New Guinea forms a broad shel tered harbor uti lized by what was the is - 5.525°S, 148.42°E; sum mit elev. 1,330 m land’s largest city prior to a major erupti on in 1994. The outer flanks of the 688-m-high asym metri cal pyroclastic Langila was last repor ted in Bul le tin v. 28 no. 3, fol low- shield vol cano are formed by thick pyroclastic-flow de pos- ing a large ash-bearing explo sion on 18 Janu ary 2003. its. The 8 x 14 km cal dera is widely breached on the E, MODIS ther mal alerts were sub se quently record ed on 9 where its floor is flooded by Blanche Bay. Two major Ho- April and 20, 23, 25, and 27 Janu ary 2004. One dayli ght locene cal dera-form ing erupti ons at Rabaul took place alert was recei ved and omit ted (22 Septem ber 2003). Day- about 7,100 and 1,400 years ago. Three small light alerts posted by the current algo rit hm are consid ered stratovolcanoes lie outside the northern and NE cal dera less re li able. No cor rob o ra tive re ports of ac tiv ity have been rims. Post-calder a erup tions built ba saltic-to-dacitic recei ved from the Rabaul Volcano Obser va tory or the Dar- pyroclastic cones on the caldera floor near the NE and win Volcanic Ash Advisory Center (VAAC). west ern cal dera walls. Sev eral of these, in clud ing Vulcan Back ground. Langila, one of the most acti ve volca noes cone, which was formed during a large erupti on in 1878, of New Brit ain, consis ts of a group of four small overlap - have pro duced ma jor ex plo sive ac tiv ity dur ing his tor i cal ping com posit e basal tic-andesitic cones on the lower east- time. A power ful explo sive erupti on in 1994 occurred si- ern flank of the exti nct Talawe vol cano. Talawe is the high - multa neousl y from Vulcan and Tavurvur vol canoes and est vol cano in the Cape Glou ces ter area of NW New forced the temporary abandonment of Rabaul city. Britain. A rect angu lar , 2.5-km-long crater is breached In for ma tion Con tact: Ima Itikarai, Rabaul Vol cano widely to the SE; Langila volcano was construc ted NE of Obser va tory (RVO), P.O. Box 386, Rabaul, Pa pua New the breached crater of Talawe. An ex ten sive lava field Guinea (Email: [email protected]). reaches the coast on the north and NE sides of Langila. Fre- quent mild-to-mod er ate ex plo sive erup tions, some times accom panied by lava flows, have been recorded since the 19th cen tury from three ac tive crat ers at the summ it of Ulawun Langila. The youn gest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m. New Britain, Papua New Guinea In for ma tion Con tacts: Rob Wright, Luke Flynn, and 5.04°S, 151.34°E; sum mit elev. 2,334 m Eric Pilger, MODIS Therm al Alert System , Hawaii In sti- tute of Geophys ics and Plane tol ogy (HIGP), School of Acti vit y on Ulawun occurs fre quently and is moni tore d Ocean and Earth Science and Technol ogy, Uni versit y of and reporte d from several sources includ ing the Rabaul Ha waii at Manoa (URL: http://modis.hgip.ha waii.edu/; Vol cano Ob ser va tory (RVO), the Dar win Vol ca nic Ash Email: [email protected] .edu, [email protected] .edu, Ad visory Center (VAAC), the U.S. Air Force Weather and [email protected]). Agency (AFWA), and imag ery from sev eral sat ellites in- cluding NOAA GMS (daylight ) and MODIS (in frared). The con tin u ing ac tiv ity af ter an erup tion on 28 Sep tem ber Rabaul 2000 (see Bul le tin v.25, no. 8) re sulted in Bul le tin reports ev ery few months since that event (Bul le tin reports on New Britain, Papua New Guinea Ulawun have appeare d in nine subsequent issues through 4.271°S, 152.203°E; sum mit elev. 688 m the end of 2003). All times are lo cal (= UTC + 10 hours) This is sue sup ple ments the Bul le tin reports with those from the Darwin VAAC archive s (ta ble 3), which include d The erupti ve ac tivit y at Tavurvur that be gan in early in for ma tion pro vided from ground, air borne, and Octo ber 2002 ceased on 17 Febru ary 2004. From 1-17 Feb- space-based sensing. RVO reports that Ulawun rem ained ru ary the ac tiv ity was char acter ized by emissions of light to quiet during Febru ary 2004. Emissions from the main vent pale ash clouds ac com pa nied by oc ca sional mod er ate ex- consis ted of white vapor being re leased at weak to moder - plosions that produced thick ash plumes. The ash plumes ate rates. No noise or night-time glow were re ported during 10 Ulawun Smithsonian Institution — Bulletin of the Global

Date Com ment

28 Sep 2000 SOURCE: AIREP, AIR NIUGINI, ANK. ERUPTION DETAILS: Vol canic Ac tiv ity reported at 28/2005Z - Ash plume to 11 km, rapid growth at top, spread ing out 30 NM to N to SW. ASH CLOUD: Latest satel lite im agery shows possi ble ash cloud extend ing 60 NM in an arc from ENE to the WSW. 29 Sep 2000 SOURCE: AIREP, AIR NIUGINI, ANK. ERUPTION DETAILS: There is ev i dence of vol canic ash on sat el lite im ag ery from 28/1800Z 30 Sep 2000 SOURCE: AIREP/Geo log i cal Sur vey Pa pua New Guinea. The Geo log i cal Sur vey con firms this erup tion and notes that limited evacu ations have com menced with the prospect of fur ther seism ic and eruptive activ ity . How ever 29/2230Z ash emissions were lim ited to in fre quent puffs. 01 Oct 2000 SOURCE: AIREP/Geo log i cal Sur vey Pa pua New Guinea. ERUP TION DETAILS: A Geo log i cal Sur vey report (@ 01/0001Z) noted the sum mit ac tivity was rela tivel y quiet for last 24 hours. QANTAS AIREP @ 30/0501Z also observe d the lack of activ ity . 29 Apr 2001 SOURCE: AIREP from PNG at 292130Z. ERUP TION DE TAILS: Air craft observe d smoke cloud up to 9 km and drifting NW and SW direc tion out to 50/70 miles radius. ASH CLOUD: Satel lite im agery [29/2132Z] shows possi ble volca nic plume extend ing 65 NM to the W and 30 NM to the N and S. 30 Apr 2001 ASH CLOUD: Ex am i na tion of lat est sat el lite im ag ery [30/0530Z] in di cates sig nif i cant erup tion has ceased. Ash plume may reach 14 km. 01 May 2001 SOURCE: Vi sual and in fra-red GMS and NOAA sat el lite im ag ery, RVO. ERUPTION DETAILS: RVO ad vise re mains on a high alert level with fur ther eruptions possi ble. ASH CLOUD: There is no evi dence of ash cloud at this time, but widesprea d cloud in the area is mak ing de tec tion dif fi cult. 03 May 2001 SOURCE: AIREP from PNG 29/4/2001 2130Z. Vi sual and in fra-red GMS and NOAA sat el lite im ag ery, RVO. ERUPTION DETAILS: A re port by an air craft of volca nic ac tivity [on 29 April] at about 2130Z with smoke/ash cloud up to 9 km, and con firmed by the RVO and sat ellites sur veil lance, ini tiated a se ries of Vol canic Ad vi so ries. The latest report from RVO this morn ing states that activ ity has mod erated. ASH CLOUD: Satel lite sur veil lance has not iden tified any ash cloud since the ini tial erup tion. 28 Aug 2001 SOURCE: GMS/NOAA Sat el lite Im ag ery. ERUP TION DE TAILS: Ash ob served on sat el lite im ag ery. Anal y sis in di cates erup tion is low level. ASH CLOUD: Ash plume 5 NM wide, extend ing 15 miles to the S of the sum mit. Ash expecte d to be below 4 km. 12 Sep 2002 SOURCE: NOAA/GMS sat el lite im ag ery. ERUPTION DETAILS: Small low level plume de tected on vis i ble sat el lite im ag ery at 11/ 2100Z. Plume extended 60 NM from sum mit in the sec tor NNW to NNE. 18 Sep 2002 SOURCE: GMS sat el lite im ag ery. ERUPTION DETAILS: Low level plume detected on vis i ble sat el lite im ag ery at 18/2100Z. ASH CLOUD: Very thin plume extends 40 NM to the WSW 19 Sep 2002 SOURCE: GMS sat el lite im ag ery. ASH CLOUD: Plume can no lon ger be de tected on lat est GMS im ag ery. 27 Sep 2002 SOURCE: GMS sat el lite im ag ery. ERUPTION DETAILS: Ash plume ob served on sat el lite im ag ery [27/]2030Z. ASH CLOUD: Nar row ash cloud extends 40 NM to SW 28 Sep 2002 SOURCE: GMS sat el lite im ag ery. ERUPTION DETAILS: Ash plume ob served on sat el lite im ag ery 2130Z. ASH CLOUD: Nar row ash cloud extends 20 NM to the NNW. 15 Oct 2002 SOURCE: GMS sat el lite im ag ery. ERUPTION DETAILS: Low level ash plume ob served on sat el lite im ag ery 15/2225Z. ASH CLOUD: Ash plume extends 20 NM N of volcano. Winds indi cate plume proba bly low level. 21 Oct 2002 SOURCE: AIREP PZ-ANF, GMS im ag ery. ERUPTION DETAILS: Smoke re ported in area, and plume ob served via GMS im ag ery. ASH CLOUD: Cloud up to 4 km, extend ing 5 NM, 30 NM wide to SE. 01 Nov 2002 SOURCE: AIREP. ERUPTIO N DE TAILS: Smoke observe d 01/0042Z drifting to NW of volcano at 3 km. 02 Nov 2002 SOURCE: AIREP AIR NIUGINI. ERUPTIO N DE TAILS: Ash observe d 02/2030Z drifting to ESE of volcano to 3 km. 11 Apr 2003 SOURCE: NOAA and GMS im agery . ERUPTIO N DE TAILS: Plume evi dent on 10/2019Z and 11/0357Z NOAA im age[s], height es ti mated be low 3 km. 14 Apr 2003 SOURCE: GMS im agery . ERUPTIO N DE TAILS: Possi ble plume evi dent on 13/2032Z, 13/2132Z and 13/2225Z [im ages], height es ti mated be low 3 km 26 Apr 2003 SOURCE: GMS im agery . ERUPTIO N DE TAILS: Possi ble plume evi dent on 26/0325Z MODIS as reporte d by KGWC/ Washing ton VAAC, height es ti mated be low 4 km. 30 Apr 2003 SOURCE: GMS and MODIS im agery . ERUPTIO N DE TAILS: Possi ble nar row low level plume evi dent on 30/0010Z MODIS and 30/ 0230Z GMS visi ble im age[s], extend ing 30 NM WNW, height esti m ated be low 3 km. 03 May 2003 SOURCE: KGWC. ERUPTIO N DE TAILS: Ash/steam plume observe d on 02/2026Z F13 DMSP Im agery . Plume extends 80 NM W of volcano, height to 4 km. 04 May 2003 SOURCE: NOAA sat el lite im ag ery. ERUPTION DETAILS: Thin low level plume ob served on 04/2053Z. Plume extends 10 NM SW of Ulawun, height es ti mated at 4 km. 06 May 2003 SOURCE: GMS sat el lite im ag ery. ERUPTION DETAILS: Thin low level plume observed on 06/2032Z. 01 Jun 2003 SOURCE: GOES9 sat el lite im ag ery. ERUPTION DETAILS: Thin low level plume observed on [May] 31/2325Z. 18 Jun 2003 SOURCE: AFWA. ERUP TION DETAILS: Faint ash/steam plume seen on 18/2206Z sat el lite im ag ery. 20 Jun 2003 SOURCE: NOAA 17. ERUP TION DETAILS: Faint plume seen on NOAA 17 20/0004Z sat el lite im ag ery. 20 Jun 2003 SOURCE: NOAA 15. ERUP TION DETAILS: Faint plume seen 20/2050Z. 23 Jun 2003 SOURCE: NOAA 15. ERUP TION DETAILS: Faint plume seen on 23/2120Z. 24 Jun 2003 SOURCE: NOAA 15. ERUP TION DETAILS: Faint plume seen on 24/2057Z. 26 Jun 2003 SOURCE: MODIS. ERUPTIO N DE TAILS: Faint plume seen on 26/0005Z ex tending 25 NM SW, height esti m ated at 4 km. 28 Jun 2003 SOURCE: NOAA 15. ERUP TION DETAILS: Faint plume seen on 28/2101Z. 02 Jul 2003 SOURCE: NOAA 15. ERUP TION DE TAILS: Thin ash plume to 5 km extend ing 25 NM WSW of sum mit on 02/2108Z. 13 Jul 2003 SOURCE: AFWA. ERUPTIO N DE TAILS: Thin ash plume to 4 km moving to the W at 10 knots [10 NM/hour or 18 km/hour]. 22 Jul 2003 SOURCE: GOES9. ERUPTIO N DE TAILS: Possi ble ash plume seen on 22/0130Z visi ble GOES im agery , extend ing 30 NM to NW, height es tim ated at 3 km. Table 3. Dates of issue and the princi pal com ments in Dar win VAAC reports con cern ing Ulawun, Septem ber 2000-July 2003. Sim ilar or dupli cate messages are not shown. In many cases ash cloud trajec tory infor m ation has been omitted. On this table, the dis tance unit Nauti cal Miles (NM) has not been convert ed to kilo m eter s (1 NM = 1.852 km (exactl y)). Courtesy of the Darwin VAAC. Volcanism Network, Volume 29, Number 2, February 2004 Ruang 11 the month. No emission was reporte d from the two N-val- Witori volcano. The post-cal dera cone of Witori, Mount ley vents. Seismicity was at a low level. Pago, may have formed less than 350 years ago. Pago has The VAAC re ports con tain nu mer ous ab bre vi a tions; grown to a height above that of the Witori cal dera rim. A how ever, a few of the terms here are in widespread use re - serie s of ten dacitic lava flows from Pago covers much of fer ring to sat el lites, me te o rol ogy, and var i ous re lated agen- the caldera floor. The youngest of these was erupted during cies (NOAA, AFWA, GOES9, MODIS, and KGWC . . . 2002-2003 from vents extend ing from the summit nearly to DMSP Im agery , etc.) or AIREP (atm ospheri c condi ti ons the NW caldera wall. reported from aircraft ). “RVO” stands for Rabaul Volcano In for ma tion Con tact: Rabaul Vol cano Ob ser va tory Ob ser va tory. Other terms may be less fa miliar: “AIR (see Rabaul). NIUGINI, ANK.” refers to a com mu ter plane in the fleet of the national airline based in Papua New Guinea. The stated dates and times are not local ones, but inste ad refer to those Manam at the zero (prime) merid ian. For exam ple, 04/2240Z means the fourth day of the stated month at 2240 UTC (i.e. “Z,” Papua New Guinea spoken as Zulu, is shorthand for Coor di nate d Univer sal 4.10°S, 145.06°E; sum mit elev. 1,807 m Time (UTC). Back ground. The sym met ri cal ba saltic-to-andesitic Ac tiv ity at Manam’s two summit craters re mained low Ulawun stratovolcano is the highest volcano of the Bis- during Febru ary 2004. The sum mit area was cloud covered marck arc, and one of Pa pua New Guinea’s most fre quently most of the month; however, when clear, both craters were acti ve. Ulawun vol cano, also known as the North Son, rises ob served re leasing white va por at weak to mod er ate rates. above the north coast of the is land of New Brit ain across a A single explo sion oc curred dur ing the month, on 14 Feb- low saddle NE of Bamus volcano, the South Son. The up- ruary at Southern Crater. A thick dark gray ash cloud and per 1,000 m of the 2,334-m-high Ulawun vol cano is weak roaring noises accom panied the explo sion. The ash unvegetated. A prom inent E-W-trending escarp m ent on the cloud rose several hundred meter s above the sum mit before south may be the re sult of large-scale slump ing. Satellitic drift ing NW of the island, result ing in fine ashfall down- cones occupy the NW and east ern flanks. A steep-walled wind. There was no night time glow observe d. valley cuts the NW side of Ulawun vol cano, and a flank Back ground: The 10-km-wide island of Manam, ly ing lava-flow complex lies to the south of this val ley. His tor ical 13 km off the northern coast of Papua New Guinea, is one erupti ons date back to the begin ning of the 18th century . of the country ’s most acti ve volca noes. Four large radial Twen ti eth-cen tury erup tions were mildly ex plo sive un til valley s extend from the unvegetated sum mit of the coni cal 1967, but after 1970 several larger erupti ons produced lava 1807-m-high ba saltic- andesitic stratovolcano to its lower flows and ba saltic pyroclastic flows, greatly modifying the flanks. These “av alanche val leys,” reg u larly spaced 90 de - summit crater. grees apart, chan nel lava flows and pyroclastic av alanches In for ma tion Con tacts: Rabaul Vol cano Ob ser va tory that have sometim es reached the coast. Five small satellitic (see Rabaul); Dar win Vol ca nic Ash Ad vi sory Cen ter center s are locat ed near the island’ s shore line on the north- (VAAC), Com mon wealth Bu reau of Me te o rol ogy, North ern ern, southern and western sides. Two sum mit crat ers are Terri tory Regional Offic e, PO Box 40050, Ca suarina , NT present; both are ac tive, al though most histor i cal erupti ons 0811, Austra lia (URL: http://www.bom.gov.au/info/vaac/; have origi nate d from the southern crater, concen tra ting Email: [email protected]). erupti ve products during the past century into the SE ava - lanche val ley. Frequent histor i cal erupti ons have been recorded at Manam since 1616. A major erupti on in 1919 Pago produced pyroclastic flows that reached the coast, and in 1957-58 pyroclastic flows desce nded all four radial valleys. New Britain, Papua New Guinea Lava flows reached the sea in 1946-47 and 1958. 5.58 S, 150.52 E; sum mit elev. 742 m In for ma tion Con tact: Rabaul Vol cano Ob ser va tory All times are lo cal (= UTC + 10 hours) (see Rabaul).

Pago was mainly quiet throughout the month of Febru - ary 2004. However, two explo sions were re ported in the Ruang early hours of 24 Febru ary . The explo sions were accom panied by thick dark grey ash clouds from the lower and up- Java, In do ne sia per vents. The ash clouds drifted SW of the vol cano re sult - 2.28°N, 125.43°E; sum mit elev. 725 m ing in fine ashfall downwind. Jet-like noises were also heard at 0140 on 24 Febru ary accom pany ing the explo - The 25 Septem ber 2002 erupti on of Ruang (Bul le tin v. sions. A weak glow was vis ible from the lower vents. 27, no.10 and v. 28, no. 8) was, accord ing to the Darwin Back ground. Pago is a young post-caldera cone that Volca nic Ash Advi sory Center (VAAC), the largest in In- was construc ted within the 5.5 x 7.5 km Witori cal dera. Ex- done sia for many years and was well observe d by satel li te ten sive pyroclastic-flow de pos its are as so ci ated with for- sensors. The erupti on cloud reached a height of ~ 20 km, mati on of the cal dera about 3,300 years ago. The gently and a pyroclastic flow to ward the SE damaged an area 1.6 sloping outer flanks of Witori vol cano consis t pri maril y of km². Al though no village was hit by the pyroclastic flow, dacitic pyroclastic-flow and airfall depos it s produced dur- two were heavily damaged by very thick ash mate rial. ing a serie s of five major explo sive erupti ons from about The Darwin VAAC and Bureau of Mete o rol ogy have 5,600 to 1,200 years ago. The Buru caldera, which may publi shed im ages and ani m ati ons of the erupti on clouds have formed around the same time, cuts the SW flank of (figure 8). The satel li tes and im ages include d those from 12 Stromboli Smithsonian Institution — Bulletin of the Global

Aqua/MODIS, GMS Java Ani m ati on, and AVHRR sen- Back ground. Ruang vol cano, not to be confused with sors. Some ash clouds disperse d towards Singa pore and Ja- the better known Raung volcano on Java, is the southern - karta. A higher level cloud re mained nearly station ary near most vol cano in the Sangihe Island arc, north of Sulawesi the tropopause (the top of the tropo sphere , where most of Island. The 4 x 5 km island vol cano rises to 725 m across a the Earth’s weather occurs). The highest cloud moved narrow strait SW of the larger Tagulandang Island. The eastwards in the stratosphere . The color/shading re flects the summit of Ruang vol cano con tains a crater par tially filled strength of the detected ash signal. by a lava dome ini tially emplaced in 1904. Explo sive erup- The TOMS scien ti sts publi shed an im age on their tions recorded since 1808 have often been ac com panied by website (figure 9), de scribed as follows: “The TOMS over- lava dome form ati on and pyroclastic flows that have pass on Septem ber 25 was too early to capture the fresh damaged inhabited areas. erupti on cloud, but ash and SO2 were evi dent on the fol low- In for ma tion Con tacts: Dar win Vol ca nic Ash Ad vi sory ing day. The aerosol signal over S Borneo is at least partly Cen ter (VAAC) (see Rabaul); Nia Haerani, Volcanological due to smoke from biom ass burning; the ash cloud from Sur vey of In do ne sia (see Karangetang); Simon A. Carn and Ruang can be seen over NE Bor neo. A data gap may be ob - Arlin Krueger, Joint Center for Earth Sys tems Technol ogy scuring any SO2 or ash im medi ate ly W of Ruang.” (NASA/UMBC), Uni ver sity of Mary land, Bal ti more County, 1000 Hill top Circle , Balti more, MD 21250, USA (URL: http://skye.gsfc.nasa.gov/).

Stromboli Ae olian Is lands, It aly 38.79°N, 15.21°E; sum mit elev. 926 m

Accord ing to avia ti on reports from the U.S. Air Force, the web cam era at Stromboli capture d shots of light ash emissions on 7 and 11 Novem ber 2003. In both cases plumes rose to ~ 2.5 km ele va ti on. The Stromboli Web video cam era showed a small explo sion on 10 De cem ber Figure 8. Night-time infra red im age of the Ruang erup tion pro cessed to highlight vol canic ash. N is towar ds the top; the local island mar gins are 2003 that produced a plume to a height of ~ 1 km above the shown, Sulawesi to the right and Bor neo to the left. The enhanced areas volcano. No ash was visi ble on satellite imagery. disclose the W portion of the plume drifting over Borneo and the higher E The Istituto Nazionale di Geofisica e Vulcanologia ash and gas cloud nearly station ary over the erup tion site. A third area of (INGV) in Catania re ported that ex plo sive ac tiv ity at ash and ice cloud is nearly invis i ble near the bottom center . Cour tesy of NASA, NOAA, and the Dar win VAAC. Stromboli’s three summ it craters in creased af ter 10 Feb ru - ary 2004, leading to signif i cant growth of the cinder cones in side the crat ers. Sev eral pow er ful ex plo sions, es pe cially from Crater 1 (the NE crater) and Crater 3 (the SW crater), sent scoriae 200 m above the rims. These power ful explo - sions led to fallout of fresh bombs and lapilli on Il Pizzo Sopra la Fossa (an area atop the volcano about 100 m above the crater ter race) in early March. As of 8 March, Strombolian ac tivit y was occur ring at the volcano, with vari ati ons in the num ber and frequency of explo sions within norm ally observe d lim its, and the inten sit y of explo - sions at the higher limit of commonly observed activity. Back ground. Spec tac u lar in can des cent night time ex- plosions at Stromboli volcano have long attra cted visi tors to the “Light house of the Medi ter ranean.” Stromboli, the NE-most of the Aeoli an Islands , has lent its name to the frequent mild ex plo sive ac tiv ity that has char ac ter ized its erupti ons throughout much of histor i cal time. The small, 926-m-high island of Stromboli is the emergent sum mit of a volcano that grew in two main erupti ve cy cles, the last of which formed the west ern porti on of the island. The Neostromboli erupti ve period from about 13,000 to 5000 years ago was followe d by form ati on of the modern Stromboli ed ifice. The ac tive summ it vents are lo cated at the head of the Sciara del Fuoco, a prom inent horse- shoe-shaped scarp formed about 5000 years ago as a result Figure 9. Ruang erupted on 25 Sep tem ber 2002. A pass the next day of the of the most re cent of a series of slope fail ures that ex tend to Earth Probe sat ellite with the To tal Ozone Map ping Spectrom eter below sea level. The modern vol cano has been construc ted (TOMS) instru ment yielded this map of SO2 con cen tra tions. Cour tesy of within this scarp, which funnels pyroclastic ejecta and lava Sim on Carn and Arlin Krueger. flows to the NW. Essen ti ally conti nu ous mild strombolian Volcanism Network, Volume 29, Number 2, February 2004 Ol Doinyo Lengai 13 ex plo sions, some times ac com pa nied by lava flows, have namesake and most prom inent feature of the Erta Ale been recorded at Stromboli for more than a millennium. Range. The 613-m-high vol cano contai ns a 0.7 x 1.6 km, In for ma tion Con tacts: Istituto Nazionale di Geofisica e el lip tical summit crater hous ing steep-sided pit crat ers. An - Vulcanologia (INGV), Sezione di Catania Pi azza Roma 2, other larger 1.8 x 3.1 km wide depres sion elongate d paral lel 95123 Catania, Italy (URL: http://www.ct.ingv.it/, Email: to the trend of the Erta Ale range is locat ed to the SE of the [email protected]); Toulouse VAAC, Météo-France, 42 Ave - sum mit and is bounded by curvilinear fault scarps on the SE nue G. Coriolis, 31057 Toulouse, France (URL: http:// side. Fresh-looking basal tic lava flows from these fissures www.meteo.fr/aeroweb/info/vaac/, Email: vaac@meteo. have poured into the caldera and local ly overflowe d its rim. fr); AGI Online news ser vice, Italy (URL: http://www.agi. The sum mit cal dera is renowned for one, or someti mes two it/). long-term lava lakes that have been active since at least 1967, or possi bly since 1906. Recent fissure erupti ons have occurred on the northern flank of Erta Ale. In for ma tion Con tacts: Carsten Pe ter, Meilenbergerstr. Erta Ale 1, D-82057 Icking-Dorfen, Germ any; Chris Heinlein, Kreuzelbergstr. 62, 76189 Karlsruhe, Germ any (Email: Ethi o pia, Af rica [email protected]); Arne Kai ser, Insti tute of Geophys - 13.60°N, 40.67°E; sum mit elev. 613 m ics, Univer sit y of Ham burg, Bundesstraße 55, 20146 Ham - burg, Germ any (Email: arne.kai [email protected]); Luigi In Febru ary 2004 an expe di ti on led by Germ an scien - Cantamessa, Geó-Découverte, 12-14 rue de Cendrier, tists vis ited Erta Ale. Af ter wards, an over flight completed CH-1201 Geneva, Swit zer land (URL: http://www.erta-ale. the sur vey of vol canic ac tiv ity. Of sig nif icance was the dis - org, Email: [email protected]), Gezahegn Yirgu, cov ery that an ear lier lava lake had largely dis ap peared. In - De part ment of Ge ol ogy and Geo phys ics, Facult y of Sci- form ati on from their report follows. ence, Addis Ababa Uni versit y, P.O. Box 1176, Addis Germ an scien ti sts were at Erta Ale during 9-13 Febru - Ababa, Ethi o pia (URL: http://www.aau.edu.et/fac ul ties/sc/ ary 2004. They explore d areas around the S crater of the ge ol ogy/Ge ol ogy.htm). volcano, which for the past several years has contai ned an active lava lake (see Bul le tins v. 28, no. 4 and v. 26, no. 12). The S crater re tained only a very small frac tion of the for - Ol Doinyo Lengai mer lava lake. When visit ed it stood ~ 15 m in di am eter , lo- cated roughly in the center of the old lake. Around the small Tan za nia, East Af rica lake were many active gas vents, and there was a hor ni to, 2.751°S, 35.902°E; sum mit elev. 2960 m about 2 m tall, on the SE side. Behind its ~ 1.5-m-high All times are lo cal (=GMT + 3 hours) walls, the lake’s lava changed lev els and occa sional lava fountai ns rose to ~ 10 m high. Ac tiv ity at Ol Doinyo Lengai has con tin ued in ter mit- On 12 Febru ary the expe di ti on team desce nded to the tently since Octo ber 2002 (Bul le tin v. 27, no. 10). (Ac cord- sec ond ter race ( ~ 90 m be low the rim) of the S crater, to the ing to Fred Belton, in that same month, Oc tober 2002, Para - sur face of the for mer lake, and ap proached the small ele - mount Picture s used the crater to shoot footage for the film vated lake. Samples of newly ejected lava were collected, “Tomb Raiders II.”). and some were given to Gezahegn Yirgu at the Univer sit y This sum mary report for 2003 is based on obser va ti ons of Addis Ababa for analy sis . Sam ples retai ned by the expe - made by Joerg Keller, Jurgis Klaudius, Fred Belton, and diti on team showed white crystal s, approx i m ately 1-2 mm Christoph Weber, as well as in for mation col lected by Celia in size, em bedded in black mate ria l. On the eve ning of 12 Nyamweru from visit s to the area. Christoph Weber most Feb ru ary the team witnessed an over flow of the lit tle lake, recent ly visit ed Lengai in Febru ary 2004, when he collec ted flooding the NW half of the second ter race. Parts of the GPS data for a new, precise crater map (fig ure 10). He also west ern lake wall even tu ally collapsed, caus ing a lava flood took tem pera ture measure m ents of fumaroles and lava wave as well as more vi olent fountaining (up to 20 m). This flows (see tables 4 and 5), and gathered lava sam ples to be event lasted approximately 2 hours. given to research departments. The en tire crater was fogged by fumaroles, which were Summary of 2003 acti vit y. During the first half of 2003, mainly active in the SE cor ner of the first ter race (~ 50 m two new hor ni tos ap peared in the cen ter of the active crater be low the rim). Gas masks were nec es sary in side the crater. at Ol Doinyo Lengai at the T49 and T58B (T48) loca ti ons From the smell and (blueish) color, these gases contai ned a (see figure 10 and capti on). A huge lava pond ap peared at high quanti ty of SO2. these lo cations and caused sev eral lava flows in all di rec- No earthquakes were felt during the visit. tions. Accord ing to Burra Gadiye, a local Lengai observe r, On 21 Febru ary a low overfli ght was made across the by mid-June unusu all y dra matic ac tivit y started at both new volcano. There were no more signs of a lava lake, and only horni tos. An expe di ti on led by Freder ick Belton in August three horni tos were ac tive. Al though the flight was made 2003 reporte d that strong de gassing and rhythm ic explo sive during the day, the glow allowed the hor nitos to be vis ible. erupti ons threw lapilli, ash, and lava spat ter to 100 m above Upon return, Chris Heinlein noted that he found photos on the hor nito. Those erupti ons, best descri bed as the web by Luigi Cantamessa showing that dur ing 15-17 Strombolian, conti nued unti l Janu ary 2004. They were ac- Novem ber 2003 the lava lake was also largely gone. com panied by several lava flows and built up the com para - Back ground. Erta Ale is an iso lated ba saltic shield vol - tively tall strato-type hor ni tos at the T49-T56B lo ca tions cano that is the most acti ve volcano in Ethi opia. The broad, and at the T48-T48B-T58B loca ti ons. The sum mit of T48B 50-km-wide volcano rises more than 600 m from below sea stood just above the former T44 hornito, but T44 itself was level in the barren Danakil depres sion. Erta Ale is the no longer visible. 14 Ol Doinyo Lengai Smithsonian Institution — Bulletin of the Global

Ob ser va tions dur ing Feb ruary 2004. An expe di ti on team in- Lo ca tion Date Tem per a ture (°C) cluding Christoph Weber and others visit ed Lengai for five days, T40 lava lake 28 Aug 1999 529 10-14 Febru ary 2004 (figures 11, Pahoehoe flow in a tube near T40 01 Sep 1999 519 12, and 13). The team used GPS Aa flow still in motion on flat ter rain (60 cm thick) 01 Sep 1999 516 to conclude that the sum mit of the Pahoehoe flow in a tube near T49B 03 Oct 2000 507 tall est hor ni to, lo cated in the cen- Aa flow still in slow mo tion on flat ter rain (25 cm thick) 03 Oct 2000 496 ter area of the ac tive crater at Ol Pahoehoe flow in a tube near T49G 11 Feb 2004 588 Doinyo Lengai (T49 or T56B lo- Pahoehoe flow in a tube near T49B 12 Feb 2004 579 ca tion), was at ap prox i mately Aa flow im mo bile and on flat terrai n (15 cm thick) 13 Feb 2004 490 2,886 m el e va tion, stand ing about Table 4. Lava temper ature measured at Ol Doinyo Lengai by a dig i tal ther mom eter (TM 914C with a stab feeler, 33 m above the surround ing crater standard K-Type). The instru m ent was used in the 0-1200° Celsius mode. Cali bra tion was made using the delta-T floor to the N. While this horni to method, where tem per ature val ues are +/- 6°C in the 0-750°C range as so ci ated with at least four rep li cate measure m ents at one spot. Cour tesy of Christoph Weber. was no longer ac tive, T48B (T58B) con tained a lava lake deep inside , which was clearly indi cat ed by noise and tremor. Observ ers in Febru ary noted effu sive and lava lake ac tivit y. Lo ca tion Date Tem per a ture (°C) This occurred at the old T49 erupti on center , also indi cat ed by the ac tivit y of T49B during obser va ti on and an acti ve F1 28 Aug 1999 70 new vent (num bered T49G by Weber, figure 13) at the N Near T49 28 Aug 1999 82 flank of T49 (T56B), about half way up from its base to the Near T49C 03 Oct 2000 75 N side. F1 03 Oct 2000 69 The hot test cracks in 20 Oct 2002 124 the crater floor F1 20 Oct 2002 78 F1 30 Jun 2003 86 Near T49C 30 Jun 2003 76 F1 12 Feb 2004 88 Table 5. Fumarole tem per atures measured at cracks in the crater floor of Ol Doinyo Lengai, using the above-de scribed digi tal therm om eter . Courtesy of Christoph Weber.

This new ac tivit y proba bly caused two collaps es (which left depres sions ) in the N flank of T49 (T56B), seen since Janu ary 2004. The T49G vent, locat ed at the upper collapse, had a steady degas sing lava lake with many overflows recorded during the Febru ary visit. Lava pene tra ted the lower col lapse at T49 and lava flows reached as far as the NW over flow. On 12 and 13 Febru ary the T49B vent spat tered lava for hours, feeding lava flows to the W (to the vicin it y of T51), and fi nally es caping into a lava tube system. The lava temper ature very close to the lava lake was measured at 588°C. Im mobile aa lava flows on flat ter rain were measured be tween 480°C and 500°C (table 5). On 7 Febru ary team mem bers Christoph Weber and R. Albiez were staying at the N slope of the neighbor ing Karimassi volcano and heard a parox ysm at T48B (T58B) lasting 30 seconds. During the visit on 10 Febru ary evi - dence of this parox ysm include d fresh lava spatter and bombs cast around T58B for a radius of ~ 100 m. Evac ua ti on projec t at Ol Doinyo Lengai. Con tri bu tors Fig ure 10. GPS-aided sketch map of the crater at Ol Doinyo Lengai made to this re port be long to a group com mit ted to creat ing and on 14 Febru ary 2004. Note the lava flow paths over the crater’s mar gin on funding evacu a ti on plans. That group is called Vol cano onto the flanks (“overflows”) that have started in the past severa l years. Haz ards Doc u men ta tion and Lo gis tic Re search (see In for - Subse quent figures (photos) help clarify the shapes and sizes of horni tos mati on Contac ts). The group is working with the local and other fea tures. Nam ing con ven tions are com pli cated by the crater’s Masaii and author i ti es on prepa ra ti ons in case of a rap idly chang ing land scape, in clud ing such pro cesses at hor ni tos as collapse , cluster ing, and overlap. For ex am ple, horni to T48, which was dangerous eruption. descri bed as hav ing collapse d in July 2000, lies on the N mar gin of the Back ground. The sym metri cal Ol Doinyo Lengai horni to labeled as T58B. The lava ponds seen by Hloben in Janu ary 2001 stratovolcano is the only volcano known to have erupted are not shown, although some of their loca tions may coin cide with later carbonatite tephras and lavas in histor i cal time. The prom i- feature s. For detail ed com pari son of crater evolu tion and nam ing con ven tions, con sult pre vi ous maps (eg., Bul le tin v. 27, no. 10). Courtesy nent vol cano, known to the Maasai as “The Mountai n of of Christoph Weber, Vol cano Ex pe di tions In ter na tional and Vol cano God,” rises abruptly above the broad plain south of Lake Haz ards Doc u men ta tion and Lo gis tic Re search. Natron in the Gregory Rift Valley . The cone-building stage Volcanism Network, Volume 29, Number 2, February 2004 Ol Doinyo Lengai 15

Figure 11. Ol Doinyo Lengai as seen in Febru ary 2004 from its sum mit, looking towar ds the activel y erupting N crater. Cour tesy Christoph Weber. Figure 13. View of Ol Doinyo Lengai looking towar ds the W, facing the lava lake at T49G and the ac tive peak at T49B. Cour tesy Christoph Weber.

depth and morphol ogy of the northern crater have changed dra mat i cally dur ing the course of his tor i cal erup tions, rang- ing from steep craters walls about 200 m deep in the mid-20th cen tury to shal low plat forms mostly filling the crater. Long-term lava effu sion in the sum mit crater begin - ning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim. In for ma tion Con tacts: Christoph Weber, Volcano Ex- pe di tions In ter na tional, Muehlweg 11, 74199 Untergruppenbach, Ger many (Email: [email protected]; URL: http://www.v-e-i.de); Celia Nyamweru, De part ment of An thro pol ogy, St. Law rence Uni ver sity, Can ton NY Figure 12. View of the tallest hor nito (T56B) at Ol Doinyo Lengai in 13617 USA (Email: [email protected]; URL: http:// Febru ary 2004. T56B sits in the cen ter of the ac tive (N) crater. The it.stlawu.edu/~cnya/); Jurgis Klaudius, IMPG, Al bert-Lud - horni to’ s sum mit was at 2,886 m ele va tion. Lava flows are visi ble in the wig-Uni versit y Freiburg, Albertstrasse 23b, 79104 foreground. Courtesy Christoph Weber. Freiburg, Germ any (Email: Jurgis.Klaudius@minpet. uni-freiburg.de); Fred er ick Belton, 3555 Philsdale Ave., of the volcano ended about 15,000 years ago and was fol- Mem phis, TN 38111 USA (Email: oldoinyolengai@ lowed by pe riodic ejecti on of natrocarbonatitic and nephe- hotmail.com; URL: http://www.oldoinyolengai.org); Vol- lin ite tephra dur ing the Ho lo cene. His tor i cal erup tions have cano Haz ards Doc u men ta tion and Lo gis tic Re search, consis ted of smaller tephra erupti ons and emission of nu- VHDL; Ger many, Muehlweg 11, 74199 Untergruppenbach, merous natrocarbonatitic lava flows on the floor of the (Email: info@volcano-s ervice .com, URL: www.vol- sum mit crater and oc casion all y down the upper flanks. The cano-service .com and http://www.mtsu.edu/~fbelton/).

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