Bul letin of the Global Vol can ism Net work Vol ume 28, Num ber 9, September 2003

Kilauea (USA) Active surface lava flows from June through mid-Oc tober ...... 2 Katmai (USA) Strong winds re suspend old ash depos its, causing a large plume and distant ashfall ...... 3 Anatahan (Mariana Is lands) Very low seis micity with no ash emissions; geo thermal ac tivity in the crater ...4 Mayon (Phil ip pines) El e vated sul fur-di ox ide flux af ter mid-Sep tem ber; crater glow in Oc to ber ...... 4 Karangetang (In do ne sia) Ash explo sions and lava av alanche s in July; overall activ ity level decline s .....5 Dukono (In do ne sia) Ash explo sions in late July through Septem ber gener ate plumes up to 250 m high.....6 Gamalama (In do ne sia) Several small ash explo sions and gas emission through late Septem ber ...... 6 Tongkoko (In do ne sia) Vol ca nic earth quakes dur ing Oc to ber 2002-Jan u ary 2003 ...... 6 Tandikat (In do ne sia) Brief ep i sode of in creased seis mic ity dur ing Jan u ary-Feb ru ary 2002 ...... 7 Dieng (In do ne sia) One shallow volca nic earthquake and a gas plume in early August ...... 7 Semeru (In do ne sia) Fre quent ash ex plo sions con tinue through Sep tem ber ...... 7 Manam (Pa pua New Guinea) Minor ashfall from Main Crater activ ity dur ing May ...... 8 Pago (Pa pua New Guinea) Minor seismic ity and vapor emissions ; no lava effu sion as of 22 May...... 8 Ulawun (Pa pua New Guinea) White vapor emissions from the main crater; offshore effer ves cence...... 9 Rabaul (Pa pua New Guinea) Fre quent ash plumes from March through early Oc tober 2003 ...... 9 Lam ing ton (Pa pua New Guinea) High-frequency earthquakes began in early July ...... 10 Ambrym (Vanuatu) Lava visi ble in six vents during Septem ber; lava lake activ ity and ash emissions .....11 Momotombo (Nic a ra gua) Some seis mic swarms and tornillos; stable fumarole tem pera ture s ...... 12 Concpecíon (Nic a ra gua) Three peri ods of ele vate d seismic ity be tween June 2002 and August 2003...... 13 Arenal (Costa Rica) Pyroclastic-flow sequence down the N and NE flanks on 5 Septem ber ...... 14 Poás (Costa Rica) Hy dro ther mally ac tive re pose con tin ues through 2002 ...... 15 Barva (Costa Rica) Two crater lakes vis ited in De cem ber 2002...... 18 Nyamuragira (DR Congo) Long-period earthquakes and swarms in July 2003 ...... 18 Nyiragongo (DR Congo) Con tin u ing lava lake ac tiv ity through mid-Au gust ...... 19 Piton de la Fournaise (In dian Ocean) Seis mic cri sis and a new SSW-flank fissure on 30 Septem ber .....19

Edi tors: Ed ward Venzke, Rick Wun derman, Devra Wexler, and Gari May berry Vol unteer Staff: Robert An drews, Don Gruber, Dave Charvonia, Jacquelyn Gluck, and Stephen 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 Kilauea Smithsonian Institution — Bulletin of the Global

from Pu`u `O`o and Kupaianaha. The area of recent lava Kilauea flows on the W side of the flow-field has been desig nate d the Mother’s Day flow, which began erupt ing on 12 May Ha waii, USA 2002 and conti nues to the present (figure 2). Through Sep- 19.425°N, 155.292°W; sum mit elev. 1,222 m All times are lo cal (= UTC - 10 hours)

During 2003, lava from Kilauea conti nued to flow down the S flanks and into the ocean at several points. The Mother’s Day flow, which began erupt ing from Pu`u `O`o on 12 May 2003, rem ained acti ve. Seism icit y gen erall y per - sisted at norm al (background) levels . A recent report from the U.S. Geolog i cal Survey, edit ed by Heliker, Swanson, and Takahashi (2003) de scribed the nearly uninterupted Pu`u `O`o-Kupaianaha erupti on that started 3 Janu ary 1983 and con tin ues to day. Lava flows. Lava en tered the sea mainly at the Figure 1. Map of se lected defor m ation sta tions at Kilauea, 2003. Cour tesy Highcastle ocean entry during 11-17 June and surface lava of HVO. flows were visi ble on the coastal flat and Pulama pali during June and July 2003. However, no lava flowed into the sea during the later half of July and into early Au gust. Defla tion that began on 8 Au- gust amounted to ~ 1.8 mrad at the Uwekahuna (UWEV) tiltmeter and ~ 4 mrad at the Pu`u `O`o tiltmeter, both lo cated near the Kilauea sum mit (figure 1). The de fla tion was ac com pa nied by a drop in the level of lava in a lava tube, as seen by field workers at mid day. In fla tion be gan later that day at 1928, and in ~ 3.5 hours ~ 3.5 mrad of infla tion was re- corded at Uwekahuna and ~ 6 mrad at Pu`u `O`o. A lava breakout occurred on 9 August be tween 0200 and 0300, ~ 1.3 km SE of the center of the Pu`u `O`o cone. A very large sheet flow emerged from the up-tube side of a root less shield formed on 21 Janu ary . Observ ers saw a lava stream up to 40 m wide. By 0600 the flow covered ~ 5.2 hectares (0.052 km2). Later in August and into Sep- tem ber, sur face lava flows were vis ible on Kilauea’s coastal flat, in some areas flowing to within 500 m of the sea. On 2 Octo ber lava be gan to flow westward af ter fill ing West Gap Pit on the W flank of Pu`u `O`o cone. Fairly vig or ous spat ter ing was vis i ble in the pit, but decrea sed to only spo- radic bursts later in the day. The flow appeare d to have stopped by 4 Octo ber when no glow was ob- served com ing from the pit. Figure 2. Map se quence showing Mother’s Day lava flows that began on 12 May 2002 (darkest shade) from the Lava flows have erupted from Pu`u `O`o cone at Kilauea as of 21 May 2002, 25 Novem ber 2002, 16 May 2003, and 10 Octo ber 2003. Modi fied 1983 through 10 Oc tober 2003 from origi nal maps cre ated by the USGS Ha wai ian Vol cano Ob ser va tory. Volcanism Network, Volume 28, Number 9, September 2003 Katmai 3 tem ber and into early Octo ber, lava was moving along the E Kilauea Volcano, Ha waii: The first 20 years: U.S. Geo log i- and W sides of the Mother’s Day flow. The E-side lava cal Survey Profes siona l Pa per 1676, Denver, CO. (menti oned previ ously as the 9 August breakout) came In for ma tion Con tact: Ha wai ian Vol cano Ob ser va tory from the 9 August root less shield, it self fed by the main (HVO), U.S. Geo log i cal Sur vey, Ha waii Vol ca noes Na- Mother’s Day tube from Pu`u `O`o. The W-side lava, tional Park, P.O. Box 51, Hilo, HI 96718, USA (URL: known as the Kohola arm of the Mother’s Day flow, http://hvo.wr.usgs.gov; Email: branched off the tube system below the root less shield. In [email protected]). early Oc tober, the E-side flow stopped moving, the W-side flow died back to a trickle, and the rootles s shield gained prom inence . By 16 Octo ber, however, the shield had partly collaps ed, leaving several drained perched ponds. Up- Katmai stream from the shield, many horni tos and small flows formed over the Mother’s Day tube. Alaska Pen in sula, USA Geo phys i cal ac tiv ity. During the second half of June 58.280°N, 154.963°W; sum mit elev. 2,047 m and into August 2003, seism icit y at the sum mit was at mod - er ate-to-high lev els, with many small, low-fre quency earth - Accord ing to the Nati onal Weather Service , strong quakes occur ring at shallow depths be neath the sum mit cal - winds in the Katmai area on 21 Septem ber 2003 picked up dera at a rate of about 1-2 per minute. Lit tle or no vol canic old, loose vol canic ash and carrie d it E. Reports of minor tremor accom pa nied the swarm at the caldera, how ever. ashfall were re ported from Kodiak Island, ~ 100 km from Volca nic tremor at Pu`u `O`o rem ained at moder ate -to-high Katmai. This phenom enon was not the result of volca nic lev els, as is the norm. A quasi-cy clic tilt pattern ended at acti vit y and no erupti on occurred. Kilauea’s sum mit and Pu`u `O`o on 13 June after lasting Andrea Steffke of the Geo phys i cal In sti tute, Uni ver sity about a week. Small peri ods of infla tion and defla tion oc- of Alaska Fair banks, re ported a rel atively large ash cloud curred dur ing July and into August. ob served in sat ellite im ages coming from the Katmai area During the defla tion on 8 August, there was an increa se on 21 Septem ber 2003. The cloud was first seen in sat elli te in small, low-fre quency earthquakes and changes in their im agery (AVHRR, GOES, and MODIS) ex tending ~ 69 km frequency content . Some larger events oc curred at depths of to the SE. The max i mum tem per a ture dif fer ence ob served a few ki lom eter s, as during the previ ous several weeks. A was -1.46°C. Dave Schneider of the Alaska Volcano Ob- magnitude 5.0 earthquake 10 km beneat h Kilauea’s centra l serva tory reporte d on 22 Septem ber 2003 that at its greatest S flank on 26 August at 2024 was the largest since 2 April extent the cloud was detec table for ~ 400 km. It was ini- 2000, which occurred in alm ost exact ly the same spot. No tially observe d by an overfly ing (high-al ti tude) jet, and sub- signif i cant dam age was done, no cracks or rockfalls were se quently iden tified in split-win dow images from AVHRR, seen, and there was no change in the erupti on. Gener all y, MODIS, and GOES satel lites. Ad di tional pi lot re ports follow ing that event and into Sep tember , summit seismic ity placed the cloud top at ~ 2.1 km alti tude. conti nued at moder ate levels with 1-2 small low-fre quency The Katmai Group of vol canoes are seis mically mon i- earthquakes per minute oc curring at shallow depths be neath tored by AVO, so it was pos sible to quickly confirm that an the summ it caldera. There were some larger events at erupti on had not taken place. SIGMETS were issued by the depths of a few ki lom eter s. Alaska Avia tion Weather Unit (AAWU) for this event and At about 1500 on 20 Septem ber 2003, first Uwekahuna an AVO In for ma tion Re lease was dis trib uted that in di cated and then Pu’u O’o started to de flate. Pu’u O’o lost ~ 1.5 that this cloud of re-sus pended ash was poten ti ally haz ard- mrad during the defla tion, and Uwekahuna lost ~ 0.9 mrad. ous to aircraft . This event is unusual in its inten sit y and ex- The de fla tion ended with a sharp infla tion in the early tent of trans port. The Katmai region is char acter ized by fre - morning on 21 Septem ber, which lasted unti l early on 22 quent high winds that can be strong enough to re-suspend Sep tember , when the tilt flat tened. large (sev eral cen tim eters in size) pumice frag ments, yet Back ground. Kilauea volcano, which overlaps the east these events typi cal ly don’t produce large, exten sive air- flank of the massive Mauna Loa shield volcano, has been borne ash clouds. Ha waii’s most ac tive vol cano dur ing his tor i cal time. Erup- Back ground. Prior to 1912, Mount Katmai was a com - tions of Kilauea are prom inent in Poly nesia n legends; writ - pound stratovolcano with four NE-SW-trending sum mits, ten doc um enta ti on extend ing back to only 1820 re cords fre - most of which were trun cated by cal dera collapse in that quent sum mit and flank lava flow erupti ons that were year. Most of the two overlap ping pre-1912 Katmai vol ca- inter spersed with peri ods of long-term lava lake acti vit y noes are Pleisto cene in age, but Ho lo cene lava flows from a that lasted un til 1924 at Halemaumau crater, within the flank vent de scend the SE flank of the SW stratovolcano summ it caldera. The 3 x 5 km caldera was formed in sev eral into the Katmai River can yon. Katmai was ini tially con sid - stages about 1500 years ago and during the 18th century ; ered to be the source of the Val ley of Ten Thousand erupti ons have also origi nate d from the lengthy E and SW Smokes ash flow in 1912. However, the 3 x 4 km wide cal - rift zones, which extend to the sea on both sides of the vol- dera of 1912 is now known to have formed as a result of the cano. About 90% of the surface of Kilauea is formed of volu m inous erupti on at nearby Novarupta volcano. The lava flows less than about 1100 years old; 70% of the vol - steep-walled young Katmai caldera has a jag ged rim that cano’s surface is younger than 600 years. A long-term rises 500-1000 m above the caldera floor and contai ns a erupti on from the E rift zone that be gan in 1983 has pro- 250-m-deep, still-rising lake. Lake wa ters have covered a duced lava flows cover ing more than 100 km2, de stroy ing small post-collaps e lava dome (Horse shoe Is land) that was nearly 200 houses and adding new coastli ne to the is land. seen on the cal dera floor at the time of the ini tial ascent to Ref er ence: Heliker, C., Swanson, D.A., and Takahashi, the caldera rim in 1916. Post-1912 glacie rs have formed on T.J. (eds), 2003, The Pu`u `O`o-Kupaianaha erupti on of a bench within Katmai caldera. 4 Anatahan Smithsonian Institution — Bulletin of the Global

In for ma tion Con tacts: Alaska Vol cano Ob ser va tory pli tude, LP events last ing up to 15 sec onds were visi ble on (AVO), a co op er a tive pro gram of the U.S. Geo log i cal Sur- the ANAT records with dom inant frequen cie s of 4-5 Hz. vey, 4200 Univer sit y Drive, Anchor age, AK 99508-4667, Some of the larger events had a short burst of 6-7 Hz en- USA (URL: http://www.avo.alaska.edu/; Email: ergy about 2.5 sec onds after the onset . The largest events [email protected]), the Geo phys i cal In sti tute, Uni ver sity were barely above background at the E Anatahan stati on of Alaska, P.O. Box 757320, Fairbanks, AK 99775-7320, (ANA2) and may have been occur ring unde tec ted for the USA (Email: [email protected]), and the Alaska past sev eral weeks. The LP events at the ANAT sta tion Di vi sion of Geo log i cal and Geo phys i cal Sur veys, 794 Uni- conti nued over the next two days at a rate of several per versit y Ave., Suite 200, Fairbanks, AK 99709, USA hour. (Email: [email protected]). Back ground. The elongate d, 9-km-long island of Anatahan in the centra l Mariana Is lands consis ts of two co- alescing vol canoes with a 2.3 x 5 km, E-W-trending sum- mit de pres sion formed by over lap ping sum mit cal de ras. Anatahan The larger western caldera is 2.3 x 3 km wide and extends eastward from the sum mit of the west ern vol cano, the is- Mariana Is lands, cen tral Pa cific Ocean land’s 788 m high point. Ponded lava flows overlai n by 16.35°N, 145.67°E; sum mit elev. 788 m pyroclastic de pos its fill the cal dera floor, whose SW side is cut by a fresh-looking smaller crater. The sum mit of the The first re corded histor i cal erupti on at Anatahan, lower east ern cone is cut by a 2-km-wide cal dera with a which began on 10 May 2003, con tin ued through that steep-walled inner crater whose floor is only 68 m above month with nearly conti nu ous ash plumes (Bul le tin v. 28, sea level. nos. 4-5). Two strong explo sions on 14 June re moved much In for ma tion Con tacts: Juan Takai Camacho and of a small lava dome that had been extrude d in the crater; Ramon Chong, Com monweal th of the Northern Mariana Is - dark ash plumes were last reporte d on 16 June, after which lands Emergency Manage m ent Offic e, P.O. Box 10007, time seis mic ity de creased sig nif i cantly (Bul le tin v. 28, no. Saipan, MP 96950 USA (URL: http://www.cnmiemo.org/, 6). Only steam ing without ash emissions was re ported by Email: [email protected] and rcchongemo@ sci en tists do ing field work im me di ately af ter wards (Bul le tin hotmail.com); Frank Trusdell, Ha wai ian Vol cano Ob ser va - v. 28, no. 7) and on overfli ghts in July. Volca nic tremor and tory, P.O. Box 51, Hawaii Nati onal Park, HI 96718-0051 other seism icit y re ported by the Com monweal th of the USA (URL: http://hvo.wr.usgs.gov/cnmi/, Email: North ern Mariana Is lands (CNMI) Emergency Man age- [email protected]). ment Of fice (EMO) per sisted into early Au gust at a rel a- tively low level. This report covers observe d acti vit y from 4 August to 5 Octo ber 2003. Seism icit y was low throughout the report pe riod and no Mayon ap par ent erup tion sig nals or po ten tial pre cur sory events oc- curred. Tremor and seis mic en ergy re lease were at low lev - Phillippines els. During 2-6 August, small long-pe riod (LP) events oc- 3.257°N, 123.685°E; sum mit elev. 2,462 m curred regu lar ly. At the end of that inter val, the num ber of All times are lo cal (= UTC + 8 hours) small LP events increa sed to several hundred in 24 hours, compared to a cou ple dozen per day ear lier in the swarm, The Phil ip pine In sti tute of Vol ca nol ogy and Seis mol- but the over all en ergy re lease in crease was not sig nif icant. ogy (PHIVOLCS) reporte d on 18 Septem ber 2003 that No LP events were reporte d again unti l mid-Septem ber. On earthquake acti vit y at Mayon had been within background 5 Sep tem ber, tremor and seis mic en ergy re lease were re- levels (< 5 events/day) since 14 August with no vol canic ported to be at their lowest levels since early July. earthquakes over the previ ous five days and moder ate vol- Overfli ghts of the volcano were made by USGS and canic gas outputs. However, the sulfur diox ide (SO2) flux at EMO person nel on 30 August and 8, 9, and 11 Septem ber. 1,237 metric tons per day (t/d) was above baseli ne levels , Obser va ti ons on these days re vealed no ash emissions , and hav ing in creased from 829 t/d since 5 Septem ber. In view the fee ble plume was domi nated by steam and lesser of in creased SO2 gas emis sions, and re cent sig nif i cant amounts of vol canic gases, mainly SO2. Sporadi c emissions earth quake oc cur rences, PHIVOLCS set the haz ard status sometim es rose above the crater rim. The E crater floor was at Alert Level 1 (on a scale of 0-5). covered by dirty, sedi m ent-laden, steam ing wa ter, and an For the period 29 Septem ber-5 Octo ber, 16 low-fre- acti ve geother mal system had mud pots, mini-gey sers, and quency volca nic earthquakes (19.0 mm am pli tude), five steam jets. Steaming wa ter and sul fu rous gases were emit - high-fre quency vol ca nic earth quakes (26.0 mm am pli tude), ted from the crater walls and floor. Obser va ti ons during an and four high-fre quency short-du ra tion vol ca nic earth- 18 Sep tember over flight were simi lar to those ear lier in the quakes (2.5 mm am pli tude) were re corded, accom panied by month, although the crater floor appeare d to be covered by weak to moder ate steam ing and no visi ble crater glow. Dur- muddy wa ter inste ad of a shallow lake. A disti nct odor of ing 6-12 Oc tober, 29 low-frequency volca nic earthquakes SO2 and blue fume were noted dur ing a he li copter inspec - (14.0 mm am pli tude), four high-frequency volca nic earth- tion of the E crater lake on 27 Septem ber. On 29 Septem - quakes (6.2 mm am pli tude), and two high-fre quency short ber, geysering was seen and the odor of H2S was pres ent in du ra tion vol ca nic earth quakes (2.0 mm am pli tude) were ad di tion to SO2. recorded, with moderate steaming and faint crater glow. By 12 Septem ber USGS and EMO had rees tab li shed the PHIVOLCS reporte d on 9 Octo ber that a faint glow had origi nal, pre-erup tion Anatahan seis mic stati on (ANAT) on been seen by telescope at the inner E porti on of the sum mit the SW caldera rim. On 15 Sep tem ber, sev eral, small-am- crater betwee n 2330 on 8 Octo ber and 0048 on 9 Oc tober, Volcanism Network, Volume 28, Number 9, September 2003 Karangetang 5 and again betwee n 1630 and 1650 on 9 Octo ber. Low-fre- tin v. 28, no. 7). Al though detai led obser va ti ons were not quency volca nic earthquakes occurred four and six times, provided by the Volcanological Survey of Indo ne sia (VSI) respec tively, during 8 and 9 Octo ber. Steam emission re- for the next two weeks, the haz ard sta tus re mained at Alert mained moder ate , with visi ble plumes barely rising above Level 2 (on a scale of 1-4). the crater rim. Mayon’s SO2 flux on 9 Oc tober rose to 2,386 VSI weekly reports from 30 June through 3 August in - t/d from 1,616 t/d on 1 October. di cated that white gas plumes from the S crater typ ically On 11 Octo ber PHIVOLCS noted persis tent and signif i - rose 350-500 m above the crater rim, night glow often ex- cant in can des cence in side the sum mit crater, ap par ently tended 25 m above the crater, and white gas plumes from from lava in the E porti on of the volcano’s conduit . Seis- the N crater rose as high as 350 m. Seis mic data showed micity over the previ ous 24 hours was rel ati vely low (three that lava av alanches and shal low volca nic earthquakes in low-fre quency vol canic earth quakes). The Alert Level was early July were sig nif icantly re duced compared to the first raised to 2, sig ni fy ing in sta bil ity that may lead to ash ex plo - half of June (table 1). sions or a magmatic eruption. During 18-20 July there were ash-produc ing explo sions Back ground. Beau ti fully sym met ri cal Mayon vol cano, and lava ava lanc hes. On 21-22 July an ash explo sion pro- which rises to 2462 m above the Albay Gulf, is the Phil ip- duced a 150-m-high ash col umn and a glowing lava ava - pines’ most acti ve volcano. The structur all y sim ple vol cano lanche flowed 350 m toward the Beha river. During the has steep upper slopes aver ag ing 35-40 de grees that are week of 28 July-3 August another glowing lava ava lanc he capped by a small sum mit crater. The histor i cal erupti ons of flowed 1,500 m toward the Beha river and 350 m toward this basal tic-andesitic vol cano date back to 1616 and range the Batang river. On 29 July vol canic tremor was re corded from Strombolian to ba saltic Plinian. Erupti ons occur pre- with a maxi m um amplitude of 0.5-2 mm. dom inate ly from the centra l conduit and have also pro- Karangetang was not include d in August re ports, but the duced lava flows that travel far down the flanks. Pyroclastic report for 1-28 Septem ber noted white gas emissions from flows and mudflows have com monly swept down many of the S crater rising 150-350 m and red glow at night reach - the approx i m ately 40 ravines that radi ate from the sum mit ing 25 m over the crater, with the N crater exhib it ing white and have of ten dev as tated pop u lated low land ar eas. gas emissions to 50-150 m above the crater. There were no Mayon’s most vi olent erupti on, in 1814, killed more than lava ava lanc hes during this pe riod. The Alert Level 1200 people and devastated several towns. remained at 2. In for ma tion Con tact: Phil ip pine In sti tute of Vol ca nol- Back ground. Karangetang (Api Siau) vol cano lies at ogy and Seismol ogy (PHIVOLCS), De part ment of Science the northern end of the is land of Siau, north of Sulawesi. and Technol ogy, PHIVOLCS Building, C.P. Gar cia Ave - The 1784-m-high stratovolcano contai ns five sum mit crat- nue, Uni versit y of the Philip pines Cam pus, Diliman, ers along a N-S line. Karangetang is one of Indo ne sia ’s Quezon City, Philip pines (URL: http://www.phivolcs. most acti ve volca noes, with more than 40 erupti ons re- dost.gov.ph/). corded since 1675 and many addi ti onal small erupti ons that were not doc u mented in the his tor i cal re cord (Cat a log of Ac tive Vol ca noes of the World). Twen ti eth-cen tury erup- tions have in cluded fre quent ex plo sive ac tiv ity some times Karangetang accom panied by pyroclastic flows and lahars. Lava dome growth has occurred in the sum mit crat ers; collaps e of lava Sangihe Is lands, In do ne sia flow fronts has also produced pyroclastic flows. 2.78°N, 125.48°E; sum mit elev. 1,784 m In for ma tion Con tacts: Dali Ahmad, Hetty Triastuty, and Nia Haerani, Volcanological Survey of Indo ne sia Ash explo sions have been frequent at Karangetang dur- (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indo ne - ing 2003 (Bul le tin v. 28, nos. 5 and 7). A red glow at night sia (Email: [email protected]; URL: http://www.vsi. and lava ava lanc hes were reporte d during 9-15 June (Bul le - esdm.go.id/).

Date (2003) Deep Vol ca nic Shal low Vol ca nic Ex plo sion Multiphase Emis sion Av a lanches Tec tonic

02 Jun-08 Jun 11 348 — 233 46 110 26 09 Jun-15 Jun 32 438 1 228 21 447 20

30 Jun-06 Jul 15 93 — 446 11 32 11 07 Jul-13 Jul 15 93 — 534 22 35 7 14 Jul-20 Jul 21 174 31 672 38 45 22 21 Jul-27 Jul 17 112 9 94 131 66 25 28 Jul-03 Aug 10 8 — 312 174 94 10

01 Sep-07 Sep 8 44 1 80 341 1 20 08 Sep-14 Sep 5 14 0 50 266 5 23 15 Sep-21 Sep 6 90 0 3 16 0 74 22 Sep-28 Sep 9 60 0 75 130 0 37

Table 1. Seis micity at Karangetang dur ing 2 June-28 Septem ber 2003. VSI did not is sue re ports for Karangetang during weeks not included in the ta ble; a dash indi cate s no data reporte d. Cour tesy of VSI. 6 Dukono Smithsonian Institution — Bulletin of the Global

Date Deep Shallow Emis sion Tec tonic Dukono (2003) Volca nic Volca nic Halmahera, Indo ne si a 1.68°N, 127.88°E; sum mit elev. 1,185 m 01-07 Sep 1 7 35 64 08-14 Sep 3 1 16 59 Volcanological Survey of Indo ne sia (VSI) reports for 15-21 Sep 0 1 12 57 June and July 2003 noted vol canic acti vit y and ash emis- 22-28 Sep 0 3 21 49 sions from Dukono. VSI re ported an ash explo sion com- Table 2. Seis micity at Gamalama during 1-28 Septem ber 2003. Courtesy mencing on 7 June, with ashfall in the Galela area (~ 7 km of VSI. from the sum mit) on 9 June (Bul le tin v. 28, no. 6). Explo - sive events had de creased by 9 June, but as of 10 June the and the seism ograph record was dom inate d by emission plume was still vis i ble on sat el lite imag ery. No ad di tional events. acti vit y was reporte d through the end of June. Volca nic acti vit y was low during 18-31 August, with Ash explo sions were again reporte d by VSI dur ing 9-23 white gas emissions and several small ash explo sions . July, with a maxi m um plume height of 1,000 m in clear White-gray ash plumes emitted from the crater reached 100 weather on 22 July (Bul le tin v. 28, no. 6). No Dukono ac- m high. Night glow was seen just above the crater rim. Re - tivit y was reporte d in the report for 21-27 July. Ash explo - corded emission and tec tonic earthquakes aver aged four sions were reported again during 28 July-3 August, with a events per day. Reduced acti vit y conti nued during 1-28 white-gray colum n, under weak pressure, rising 15-75 m. Septem ber 2003, again with white gas emission and small Some explo sions produced dark-gray ash colum ns reaching ash ex plo sions that oc curred sev eral times. Seis micity was 95-450 m high. On 27 and 28 July some blasting sounds dom inate d by tectoni c and emission events (ta ble 2). The were heard in the Galela area and con tin u ous blasting hazard status since 18 August has been at Alert Level 2 (on sounds were heard on 25, 26, and 29 July. Mi nor ash fell a scale of 1-4). around the crater, and ash drifted E, SE, and NE. Back ground. Gamalama (Peak of Ternate) is a Ash ex plo sions con tin ued dur ing 18-31 Au gust, pro- near-con ical stratovolcano that com prises the en tire island ducing a gray ash plume 75 m high and an ash colum n that of Ternate off the west ern coast of Halmahera and is one of rose 200-250 m accom panied by boom ing sounds. VSI re- In do ne sia’s most ac tive vol ca noes. The is land of Ternate ported that ash explo sions during the 1-28 Septem ber pe- was a major regional center in the Portu guese and Dutch riod produced a gray ash plume 50-200 m high. When there spice trade for several centu rie s, which contri buted to the was no explo sive acti vit y, white-gray ash emissions were thor ough doc u men ta tion of Gamalama’s his tor i cal ac tiv ity. observe d rising 50 m from the crater. The hazard status has Three cones, progres sive ly younger to the N, form the sum - re mained at Alert Level 2 (on a scale of 1-4) since early mit of Gamalama, which reaches 1715 m. Sev eral maars June. and vents de fine a rift zone, par allel to the Halmahera is- Back ground. Reports from this rem ote vol cano in land arc, that cuts the volcano. Erupti ons, recorded fre- northern m ost Halmahera are rare, but Dukono has been one quently since the 16th century , typi cal ly origi nate d from the of Indo ne sia ’s most acti ve volca noes. More or less conti nu - sum mit crat ers, although flank erupti ons have occurred in ous ex plo sive erup tions, some times ac com pa nied by lava 1763, 1770, 1775, and 1962-63. flows, occurred since 1933 unti l at least the mid-1990s, In for ma tion Con tact: Dali Ahmad, Volcanological when routi ne obser va ti ons were curtai led. During a major Survey of Indo ne sia (VSI) (see Karengetang). erupti on in 1550, a lava flow filled in the strait betwee n Halmahera and the N-flank cone of Gunung Mamuya. Dukono is a com plex vol cano pre sent ing a broad, low pro- file with multi ple sum mit peaks and overlap ping craters. Tongkoko Malupang Wariang, 1 km SW of Dukono’s sum mit crater com plex, contai ns a 700 x 570 m crater that has also been Sulawesi, In do ne sia active during historical time. 1.52°N, 125.20°E; sum mit elev. 1,149 m In for ma tion Con tacts: Dali Ahmad and Nia Haerani, Volcanological Survey of Indo ne sia (VSI) (see The Volcanological Survey of Indo ne sia (VSI) reporte d Karengetang). deep vol canic and A-type earthquakes at Tongkoko (also known as Tangkoko) over the period 7 Oc tober-24 Novem - ber 2002 and more deep-volca nic events during 23 De cem - ber 2002-19 Janu ary 2003 (ta ble 3). The earthquakes , Gamalama which began in May 2002, were recorded fol lowing re loca - tion of an obser va tory post to Wainenet village in the Halmahera, Indo ne si a Bitung area. The tem pera ture at Batu Angus hot spring on 0.80°N, 127.325°E; sum mit elev. 1,715 m 10 Octo ber 2002 was 70-73°C. While no visi ble acti vit y has been ob served, the haz ard sta tus was raised to Alert An erupti ve event on 31 July 2003 at Gamalama pro- Level 2 (on a scale of 1-4) on 24 Octo ber 2002 as a result of duced ashfall and pyroclastic flows (Bul le tin v. 28, no. 7). the in creased seis micity. The last re corded ac tiv ity at The Volcanological Survey of Indo ne sia (VSI) report for Tongkoko consis ted of flank lava flows and lava dome ex- the week of 28 July-3 August noted that the haz ard status trusion in 1880. was downgraded to Alert Level 3 on 2 August. A white gas Back ground. The NE-most vol cano on the is land of plume was reporte d as rising 10-50 m above the sum mit Sulawesi, Tongkoko has a sum mit that is elongate d in a Volcanism Network, Volume 28, Number 9, September 2003 Semeru 7

volcano. Vol canic acti vit y has migrat ed to the SSW from Date Deep A-type Tec tonic Singgalang and only Tandikat has had histor i cal acti vit y. (2002-03) Volcanic The sum mit of Tandikat has a parti ally eroded 1.2-km-wide crater con tain ing a large cen tral cone capped by a 07 Oct-13 Oct 4 — — 360-m-wide crater with a small crater lake. The only three 14 Oct-20 Oct — 12 23 reporte d histor i cal erupti ons, in the late 19th and early 20th 21 Oct-27 Oct — 9 34 centu rie s, produced only mild explosive activity. 28 Oct-03 Nov — 17 19 In for ma tion Con tact: Dali Ahmad, Volcanological 04 Nov-10 Nov — 9 38 Survey of Indo ne sia (VSI) (see Karengetang). 11 Nov-18 Nov — 2 37 19 Nov-24 Nov — 2 25 23 Dec-29 Dec 5 — 16 06 Jan-12 Jan 11 — 21 Dieng 13 Jan-19 Jan 5 — 28 Java, In do ne sia Table 3. Earthquakes recorde d at Tongkoko, 7 Oc tober 2002-19 Janu ary 7.20°S, 109.92°E; sum mit elev. 2565 m 2003. In addi tion, one shal low volca nic event was recorde d during 13-19 Janu ary 2003, and single B-type earthquakes each occurr ed during 21-27 The Volcanological Survey of Indo nesia (VSI) ac tiv ity Octo ber and 4-10 Novem ber 2002. Courtesy of VSI. report for the week of 4-10 August 2003 noted, for the Sileri crater in the Dieng vol cano com plex, one shallow NW-SE direc ti on with a large deep crater that in 1801 con- volca nic earthquake, a white gas plume rising 25-60 m, and tained a cone surrounded by lake water . The slightly higher wa ter tem per ature of 83°C. The haz ard sta tus was set at Dua Saudara stratovolcano is locat ed only 3 km to the SW Alert Level 2 (on a scale of 1-4). of Tongkoko, and along with Tongkoko, forms the most Back ground. The Dieng pla teau in the highlands of prom inent feature s of Gunung Dua Saudara Nati onal Park, centra l Java is renowned both for the vari ety of its volca nic a noted wildli fe preserve . Erupti ons occurred from the sum - scen ery and as a sacred area hous ing Java’s old est Hindu mit crater of Tongkoko in the 17th century and in 1801. The tem ples, dat ing back to the 9th century AD. The Dieng vol - prom inent, flat-topped lava dome Batu Angus formed on canic com plex consis ts of two or more stratovolcanoes and the E flank of Tongkoko in 1801, and, along with an adja - more than 20 small crat ers and cones of Pleisto cene -to-Ho- cent E-flank vent, has been the source of all subsequent locene age over a 6 x 14 km area. Prahu stratovolcano was eruptions. trun cated by a large Pleisto cene cal dera, which was sub se - In for ma tion Con tact: Dali Ahmad, Hetty Triastuty, Nia quently filled by a se ries of dis sected to youthful cones, Haerani, and Suswati, Volcanological Survey of Indo ne sia lava domes, and crat ers, many con tain ing lakes. Lava flows (VSI) (see Karengetang). cover much of the pla teau, but have not oc curred in histor i - cal time, when activ ity has been restricted to minor phreatic erupti ons. Toxic volca nic gas emission has caused fa tal iti es Tandikat and is a hazard at sev eral crat ers. The abun dant ther mal fea - tures that dot the platea u and high heat flow make Dieng a Sum atr a, Indo ne si a major geothermal prospect. 0.433°S, 100.317°E; sum mit elev. 2,438 m In for ma tion Con tact: Dali Ahmad and Nia Haerani, Volcanological Survey of Indo ne sia (VSI) (see Vol ca nic seis mic ity at Tandikat in creased sig nif i cantly Karengetang). follow ing a felt event (MM III) on 20 Janu ary 2002 (ta ble 4). Deep-volca nic earthquakes total ed 149 during the week of 20-26 Janu ary , a period when 174 tec tonic events were Semeru also recorded. Both types of earthquakes decrea sed signif i - cantly the next week, and gradu all y de clined further over Java, In do ne sia the follow ing two weeks. The weekly report for 27 Janu - 8.108°S, 112.92°E; sum mit elev. 3,676 m ary-2 Febru ary noted that vi sual obser va ti ons were not pos- sible due to thick fog. The hazard status was set at Alert Vol canic ac tiv ity at Semeru between 30 June and 28 Level 2 (on a scale of 1-4) on 25 Janu ary 2002 and Septem ber rem ained at high levels . Except for the middle remained at that level through 16 February. two weeks of July, ash explo sions were re ported several Back ground. Tandikat and its twin volcano to the NNE, times every week, produc ing white-gray plumes that rose Singgalang, lie across the Bukittinggi plain from Marapi 400-500 m above the sum mit. Re corded seis mic data (table 5) refle cted this conti nued ac tiv- Date Shal low Deep ity, with betwee n 447 and 804 ex- Emis sion Tremor Tec tonic (2002) Vol ca nic Vol ca nic plosion events weekly (~ 88 per day on aver age over this 90-day 13 Jan-19 Jan — 6 — — 22 pe riod). Av a lanche events, 20 Jan-26 Jan 1 149 — 2 174 tremor, tec tonic, deep-vol ca nic, 27 Jan-02 Feb — 46 4 1 54 shal low-vol ca nic, and flood-re- 03 Feb-09 Feb — 24 3 — 18 lated seis micity were also re- 10 Feb-16 Feb — 19 5 — 15 corded. A pilot report from Qantas noted a plume to twice the Table 4. Seis micity recorde d at Tandikat, 13 Janu ary -16 Febru ary 2002. Cour tesy of VSI. height of the volcano (~ 7.2 km 8 Manam Smithsonian Institution — Bulletin of the Global

volcano was quiet over the pe riod Date (2003) Ex plo sion Av a lanche Tremor Other Tectonic 25-30 June, with both crat ers gently re leas ing oc ca sional thin 30 Jun-06 Jul 611 7 6 — 7 white vapor emissions and low 07 Jul-13 Jul 615 10 18 2 deep 9 seismicity. 14 Jul-20 Jul 579 19 1 — 8 Back ground. The 21 Jul-27 Jul 529 11 7 — 10 10-km-wide island of Manam, ly - 28 Jul-03 Aug 447 21 5 — 6 ing 13 km off the N coast of Pa- 04 Aug-10 Aug 499 20 10 1 shallow 5 pua New Guinea, is one of the 11 Aug-17 Aug 550 8 16 — 6 coun try’s most ac tive vol ca noes. 18 Aug-24 Aug 516 13 2 1 shallow 10 Four large ra dial val leys ex tend 25 Aug-31 Aug 804 11 1 — 7 from the unvegetated sum mit of 01 Sep-07 Sep 735 12 0 0 6 the con i cal 1,807-m-high 08 Sep-14 Sep 699 30 1 1 flood 5 stratovolcano to its lower flanks. 15 Sep-21 Sep 731 11 5 0 8 These “av a lanche val leys,” reg u- 22 Sep-28 Sep 636 20 9 0 4 larly spaced 90 de grees apart, Table 5. Seis micity at Semeru, 30 June-28 Septem ber 2003. Courtesy of VSI. chan nel lava flows and pyroclastic av alanches that have sometim es reached the coast. Five alti tude) on 9 Septem ber that was drift ing S. The haz ard small satellitic cen ters are lo cated near the island’s shore- sta tus re mained at Alert Level 2 throughout the report line on the northern, southern and western sides. Two sum - period. mit craters are pres ent; both are ac tive, al though most his- Back ground. Semeru, the highest volcano on Java, and tori cal erupti ons have origi nate d from the southern crater, one of its most acti ve, lies at the southern end of a volca nic con cen trat ing erup tive prod ucts dur ing the past cen tury into massif extend ing north to the Tengger caldera. The the SE av a lanche val ley. Fre quent his tor i cal erup tions have steep-sided vol cano, also re ferred to as Mahameru (Great been re corded at Manam since 1616. A major erupti on in Mountai n), rises abruptly to 3,676 m above coastal plains to 1919 produced pyroclastic flows that reached the coast, and the S. Gunung Semeru was construc ted S of the overlap - in 1957-58 pyroclastic flows de scended all four ra dial ping Ajek-ajek and Jambangan calde ras. A line of valleys. Lava flows reached the sea in 1946-47 and 1958. lake-filled maars was con structed along a N-S trend cut ting In for ma tion Con tact: Ima Itikarai, Rabaul through the sum mit, and cinder cones and lava domes oc- Volcanological Obser va tory , P.O. Box 386, Rabaul, Papua cupy the east ern and NE flanks. Sum mit topog ra phy is New Guinea. com pli cated by the shift ing of crat ers from NW to SE. Fre- quent 19th and 20th century erupti ons were dom inate d by small-to-mod er ate ex plo sions from the summit crater, with Pago occa siona l lava flows and larger explo sive erupti ons ac- com panied by pyroclastic flows that have reached the lower New Britain, Papua New Guinea flanks of the volcano. Semeru has been in almost 5.58°S, 150.52°E; sum mit elev. 742 m continuous eruption since 1967. In for ma tion Con tacts: Dali Ahmad and Nia Haerani, The erupti on at Pago that began in August 2002 conti n - Volcanological Sur vey of In do ne sia (VSI)Volcanological ued during early 2003 with lava effu sion through at least 28 Survey of Indo ne sia (VSI) (see Karengetang); Dar win Vol- Feb ru ary and va por emis sions (Bul le tin v. 28, no. 3). The ca nic Ash Ad vi sory Cen tre (VAAC), Bu reau of Me te o rol- Rabaul Volcanological Obser va tory (RVO) re ports that ac- ogy, Northern Terri tory Regional Offic e, PO Box 40050, tivit y at Pago conti nued, but rem ained low, from 14 April Ca sua rina, NT 0811, Aus tra lia (URL: http://www.bom. through 9 October 2003. gov.au/info/vaac/). The line of vents on the NW slope of Pago conti nued to relea se small amounts of thin white va por over the whole of the pe riod. Oc casiona l weak audi ble boom ing noises were Manam heard (eg. on 20 April) and roar ing noises were heard on 24 April, 6 May, and 22 May. Very small traces of blue vapor Papua New Guinea were seen com ing from the lower vents on 8 May. 4.10°S, 145.061°E; sum mit elev. 1,807 m An aeria l inspec tion on 22 May showed that lava effu - sion from the NW vent had ceased since the Febru ary in- Recent ac tiv ity at Manam has con sisted of white va por spec tion; there were no indi ca ti ons of fresh lava near the emissions from both the Main and Southern craters, and vent, no movem ent of the N and S lobes, and no change in low seis mic ity (Bul le tin v. 28, no. 3). The Rabaul the height of lava against the cal dera wall. It also re vealed a Volcanological Obser va tory reporte d that the two vents in new fumarolic area to the E. the Main crater gently re leased weak, thin white va por dur - Moni tor ing instru m ents were re stored on 19 May. Lev- ing 7-12 May, with occa siona l white-gray emissions on 11 el ing mea sure ments showed a few cen ti me ters of in fla tion May. Fine ashfall result ing from occa siona l emissions of com pared to Decem ber 2002. This was consid ered by RVO thin white gray ash plumes from Main crater was reporte d to be very signif i cant when com pared to previ ous measure - on the NW side of the is land on 17-19 and 23 May. No au - ments, but may have been due to nearby roadwork. dible noise or glow was re ported. Southern crater conti nued Less than 20 vol cano-tectoni c earthquakes per day were to gently relea se small amounts of thin white va por. The recorded during 25-30 June. A local tec tonic earthquake on Volcanism Network, Volume 28, Number 9, September 2003 Rabaul 9

9 Au gust seemed to lead to an in crease in en ergy re lease marck arc, and one of Pa pua New Guinea’s most fre quently and event num bers at one seis mic stati on, but it may have acti ve. Ulawun vol cano, also known as the North Son, rises been an in stru men ta tion prob lem. An air borne above the north coast of the is land of New Brit ain across a spectrophotometer reveal ed only trace amounts of SO2 in low saddle NE of Bamus volcano, the South Son. The up- early August. Betwee n two and seven volcano-t ectoni c per 1000 m of the 2334-m-high Ulawun vol cano is earthquakes per day were re ported in the 26 Septem ber-9 unvegetated. A prom inent E-W-trending escarp m ent on the October period. south may be the re sult of large-scale slump ing. Satellitic Back ground. Pago is a young post-caldera cone that cones occupy the NW and east ern flanks. A steep-walled was construc ted within the 5.5 x 7.5 km Witori cal dera. Ex- valley cuts the NW side of Ulawun vol cano, and a flank ten sive pyroclastic-flow de pos its are as so ci ated with for- lava-flow complex lies to the south of this val ley. His tor ical mati on of the cal dera about 3300 years ago. The gently erupti ons date back to the begin ning of the 18th century . sloping outer flanks of Witori vol cano consis t pri maril y of Twen ti eth-cen tury erup tions were mildly ex plo sive un til dacitic pyroclastic-flow and airfall depos it s produced dur- 1967, but after 1970 several larger erupti ons produced lava ing a serie s of five major explo sive erupti ons from about flows and ba saltic pyroclastic flows, greatly modifying the 5600 to 1200 years ago. The Buru caldera, which may have summit crater. formed around the same time, cuts the SW flank of Witori In for ma tion Con tact: Ima Itikarai, Rabaul volcano. The post-cal dera cone of Witori, Mount Pago, Volcanological Ob ser va tory (see Manam); Dar win Vol ca- may have formed less than 350 years ago. Pago has grown nic Ash Advi sory Centre (VAAC), Bu reau of Me te o rol ogy, to a height above that of the Witori cal dera rim. A serie s of Northern Terri tory Regional Offic e, PO Box 40050, Ca sua- ten dacitic lava flows from Pago cov ers much of the caldera rina, NT 0811, Aus tra lia (URL: http://www.bom.gov. floor. The youngest of these was erupted during 2002-2003 au/info/vaac/). from vents extend ing from the summit nearly to the NW caldera wall. In for ma tion Con tact: Ima Itikarai, Rabaul Rabaul Volcanological Ob ser va tory (see Manam). New Britain, Papua New Guinea 4.271°S, 152.203°E; sum mit elev. 688 m Ulawun Reports from the Rabaul Volcanological Obser va tory New Britain, Papua New Guinea (RVO) over the period 20 March-9 Oc tober show that ash 5.05°S, 151.33°W; sum mit elev. 2,334 m erupti ons from the Tavurvur cone at Rabaul are conti nu ing. Acti vit y has been nearly con tinu ous since the major Sep- Vari able amounts of emergent va por and minor debris tem ber 1994 erupti on (Bul le tin v. 19, no. 8). flows at Ulawun were reporte d during Janu ary -March 2003 Erupti ons during 20 March-6 April were charac ter ized (Bul le tin v. 28, no. 03). Rabaul Volcanological Obser va tory by discret e, slow, convo lut ed ash plumes oc curring at long (RVO) re ports, cover ing much of the period 14 April-5 Oc - ir reg u lar in ter vals ris ing slowly to sev eral hun dred me ters tober 2003, indi cat ed the volcano re mained quiet over this over the sum mit. The ash plumes were mainly light to pale time, with out emission s from the N-val ley vent. gray, blow ing to the SE. Seis micity was gen er ally low, with The main summ it crater con tin ued to release weak to low- to inter medi ate -frequency events of 1-5 minute dura - mod er ate vol umes of white (oc ca sion ally white-gray) va por tion asso ci ate d with the ash emissions , and greater energy during 14-29 April, 7-27 May, and 11-18 June. Seism icit y expended over the first 10 sec onds of the more forceful was low except for an epi sode of vol canic tremor betwee n erupti ons. Ground defor m ati on fluctuated without showing 15 and 19 April. Gas ef fer ves cence was repor ted close off - any real trends. shore of Ulamona Jetty in the second half of April. A slight Short forceful and slow sub-conti nu ous dis crete ash increa se in seism icit y was noted between 18 and 23 May. emissions were re ported for 7-29 April. Light to pale gray The pe riod 25 June-22 July was quiet, with no audi ble ash-laden plumes rose as high as 1,500 m over the sum mit, noise or night-time glow, and weak to moder ate volum es of blowing NW and SE on vari able winds, with ash accu m ula - vapor from the main sum mit crater. The Volca nic Ash Ad- tion in Rabaul Town to the NW. Seis micity was gen er ally visory Center in Darwin re ported these plumes as being vis- low and re flected the erup tive ac tiv ity. Most ac tiv ity in- ible on weather sat ellite im ag ery. The plumes appeared volved low-frequency , low-am pli tude short- to long-dura - white-gray on occa sions and were unusu all y strong bluish tion sub-con tin u ous vol ca nic trem ors. Some high-fre- white gray over the last three days of the period. Vol canic quency earthquakes were re corded NE of Rabaul Town. seis micity was low, with sev eral strongly felt tec tonic Deformation measurements showed minor inflation. earthquakes on the night of 3-4 July. A large re gional earth - Steady ash erupti ons conti nued during 7-12 May. While quake cen tered 45 km N of Rabaul af fected the area on 16 the ash content in indi vid ual plumes was fairly low, the ac - July, lead ing to a large tiltmeter off set, which slowly cum ula ti on of ash on the ground becam e quite signif i cant recovered over the following days. within 5 km of the volcano. Seis micit y was gener all y low Reports for the pe riod 12 Septem ber-5 Octo ber indi - (low-fre quency earthquakes with dura ti ons of several min- cated that the main summ it con tin ued to release weak to utes), re flect ing summit activ ity. This in creased to mod er - moder ate volum es of white va por, with occa siona l ate seismicity over 10-12 May. Short-term ground-defor - white-gray emis sions. Seis micity was low with no sig nif i- ma tion mea sure ments were am big u ous; long-term trends cant ground movements. showed minor inflation. Back ground. The sym met ri cal ba saltic-to-andesitic There was a no ticeable de cline in ash erup tions and Ulawun stratovolcano is the highest volcano of the Bis- seism icit y during 19-30 June, from one every few minutes 10 Lam ing ton Smithsonian Institution — Bulletin of the Global to less than one per hour and then com plete cessa ti on on 29 volcano are formed by thick pyroclastic-flow de posit s. The June. Very oc casional low roar ing noises were heard early 8 x 14 km cal dera is widely breached on the east, where its in the period. Tavurvur re leased only variable amounts of floor is flooded by Blanche Bay. Two major Holo cene cal - thin white vapor through 9 August. It began to erupt again dera-form ing erupti ons at Rabaul took place about 7100 on 10 August, with slow convo lut ed emissions of mainly and 1400 years ago. Three small stratovolcanoes lie outside white to pale-gray ash at irreg u lar inter vals blowing to the the northern and NE cal dera rims. Post-cal dera erupti ons NW, includ ing over the Rabaul Town area. Discret e moder - built ba saltic-to-dacitic pyroclastic cones on the cal dera ate to large explo sions began to oc cur on 25 August (1-3 floor near the NE and western cal dera walls. Sev eral of per day). Occa siona l low rum bling noises were heard. Seis- these, includ ing Vul can cone, which was formed during a mic acti vit y was low and there were no significant ground large erupti on in 1878, have produced major explo sive ac- movements. tiv ity dur ing his tor i cal time. A pow er ful ex plo sive erup tion From 29 August to 11 Septem ber the level of erupti ve in 1994 occurred sim ulta neousl y from Vulcan and ac tiv ity was low to mod er ate, char ac ter ized by con vo luted Tavurvur vol canoes and forced the temporary abandonment ash clouds at short ir reg u lar in ter vals. Mod er ate ex plo sions of Rabaul city. (3-6 per day) produced thick colum ns of pale gray to dark In for ma tion Con tacts: Ima Itikarai and Steve ash clouds rising 2-4 km above the sum mit. The pre vail ing Saunders, Rabaul Volcanological Obser va tory (see SE winds result ed in ashfall to the NW, includ ing in the Manam); Wil liam Kiene, UCLA, 405 Hilgard Ave nue, Box Rabaul Town area. Seis mic activ ity was low, with some 951361, Los Angele s, CA 90095-1361 (Email: high-fre quency earthquakes NE of Rabaul Caldera and no [email protected]). sig nif i cant ground-deformation movements. The level of erupti ve ac tivit y was gener all y low during 12-25 Septem ber (figure 3), with light to pale gray ash Lam ing ton clouds rising 500-1,500 m above the sum mit and light downwind ashfall in the early part of the report ing period. Papua New Guinea Over 22-25 Septem ber the ash cloud emissions becam e 8.95°S, 148.15°E; sum mit elev. 1,680 m light gray, with high water vapor content . Low to moder ate rum bling noises were heard, but seism ic acti vit y was low The Rabaul Volcanological Obser va tory reporte d that and ground defor m ati on movem ents were not significant. Lam ington re mained quiet over the period 25 June-9 Octo - Erupti ve ac tivit y con tinued at a low level from 26 Sep- ber 2003. Va por emissions were diffi cult to observe be- tem ber to 9 Octo ber, with light to pale gray emissions (con- cause of the dis tance to the obser va ti on point, but on a few taining some ash but mostly wa ter vapor) ris ing 500-1,500 clear days very small volum es of thin white va por were m. The emissions occurred at long, irreg u lar inter vals, and seen in the sum mit area. The re port also noted that high-fre- many were accom panied by low roaring and rum bling quency volcano-t ectoni c-like earthquakes began in early noises. Very fine ash was blown mainly to the N and NW. July at a rate of up to five events per day and conti nued into Seism ic acti vit y was low, with no high-fre quency earth- early Oc to ber. This is the first time since the seis mic station quakes inside the caldera or NE of the cal dera. Ground-de- was re-estab li shed in 1997 that these types of earthquakes for ma tion mea sure ments showed a long-term in fla tion ary have been recorded in signif i cant numbers over a short trend betwee n May and Septem ber, but the magnitude of period of time. change was small. Back ground. Lam ington is an andesitic stratovolcano Back ground. The low-ly ing Rabaul cal dera on the tip with a 1.3-km-wide breached sum mit crater contai ning a of the Gazelle Pen in sula at NE end of New Brit ain forms a lava dome. Prior to its re nowned devas tat ing erupti on in broad shelter ed harbor uti lized by what was the is land’s 1951, the forest ed peak had not been rec ognize d as a vol- largest city prior to a major erupti on in 1994. The outer cano. Mount Lam ington rises to 1680 m above the coastal flanks of the 688-m-high asym metri cal pyroclastic shield plain north of the Owen Stanley Range. A sum mit com plex of lava domes and crater remnants rises above a low-an gle base of volcaniclastic de pos its that are dis sected by ra dial val leys. A prom i nent broad “av a lanche val- ley” extends northward from the breached crater. Mount Laming - ton sprang suddenly to life in 1951, pro duc ing a pow er ful ex- plo sive erup tion dur ing which dev as tat ing pyroclastic flows and surges swept all sides of the vol- cano, kill ing nearly 3000 persons. The erupti on conclude d with growth of a 560-m-high lava dome in the summit crater. In for ma tion Con tact: Ima Figure 3. Photo graph show ing a plume from the Tavurvur cone at Rabaul (left background) taken from the Rabaul Itikarai, Rabaul Volcanological Volcanological Obser va tory , with Rabaul Town and Harbor in the fore ground, 17 Septem ber 2003. Courtesy of Ob ser va tory (see Manam). Wil liam Kiene, UCLA. Volcanism Network, Volume 28, Number 9, September 2003 Ambrym 11

sim i lar i ties in lo ca tion, size, and dy nam ics com pared to De - Ambrym cem ber 2002. The 50-m-di am eter lava lake was con tained inside a circu lar funnel- shaped pit 100-120 m in di am eter . Ambrym Island, Vanuatu Vio lent agi ta ti on of the surface occurred most of the time. 16.25°S, 168.12°E; sum mit elev. 1,334 m Lava splashed onto the pit walls and drained back vertically All times are lo cal (= UTC + 11 hours) 25 m into the pit. Large 10-m-diam eter gas bubbles burst in the SE half of John Seach previ ously reporte d his obser va ti ons of the the lava lake with up to eight bubbles visi ble at the same Ambrym caldera made during a visit in Decem ber 2002 time. Jets of lava were ejected ev ery few sec onds, cre ated (Bul le tin v. 27, no.12). This report contains his obser va - by wave inter sec tions from the bursting bubbles . During tions of the cal dera during a 7-11 Sep tem ber 2003 visit and periods of low acti vit y, last ing tens of seconds, lava drained flyovers on 6 and 13 Sep tem ber. The level of activ ity dur - back into the middle of the pit. Surface crust ing occurred ing Septem ber 2003, with visi ble lava in six vents, was after as lit tle as one minute dur ing quiet pe riods. Subse - higher than that during his previous visit. quently, the crust was broken up by a resum pti on of degas - Ob ser va tions of Benbow. During the 6 Sep tem ber fly- sing from the SW side of the pit. On several occa sions , up over, two white plumes were rising 200 m above the crater to 80% of the lava lake surface was covered by darker crust. rim and drifting NW. On the evening of 7 Sep tem ber, or- Acid rain was ex pe ri enced on the edge of the crater and ange glows were seen from the caldera edge (3 km SE). A observ ers felt minor burning on the face. White, strong glow origi nate d N of the crater and the centra l crater light-brown, and blue-tinged vapors smell ing of sul fur were pit produced a less intens e fluctu at ing glow. During the 13 emitted from the crater. Septem ber flyover, both pits conti nued to emit white and Mbwelesu was scaled again on 10 Septem ber and ob- light-brown plumes to 200 m above the rim. serva ti ons of the lava lake (figure 4) were made over eight Obser va ti ons of Mbogon Niri Mbwelesu. Large white hours. The crater was clear, en abling detailed ob ser va tions. vapor emissions from the collaps e pit formed mush- At times 80% of the lake surface was de formed by bub- room-shaped clouds on 6 Septem ber that drifted W and at - bling. The SE porti on of the pit contai ned the most de gas- tained a height of 300 m. A visit to the S rim on 7 Sep tem - sing. Vi o lent ex plo sions reg u larly sprayed or ange lava ber showed a weak orange glow and copi ous gas emissions . mixed with black crust in all di recti ons. At one point the On 8 Septem ber, obser va ti ons from the N rim showed the whole lake sur face ro tated clock wise and lava drained back pit full of swirling brown and white vapor. The NW wall into the middle of the pit. This whirlpool was followe d by was stained with yellow and red depos it s, and pungent sul- an ava lanc he on the W side of the pit that threw black mate - furous gases were being emit ted. Loud, rhythm ic de gassing rial into the lake. A second pit with a diam eter of 75 m NE sounds were heard every few seconds. The bottom of the pit of the lava lake was sepa rat ed by an unstable 10-m-wide was visi ble on 10 Septem ber, allow ing views of two glow- wall from which num erous ava lanc hes oc curred dur ing the ing red holes 150 m below the rim sepa rat ed by a small wall day; red lava spat ter was ejected once. a few meters wide. The two vents degassed sim ul taneou sly, An after noon fly over on 13 Sep tem ber en abled ex cel- but the E vent emitted larger amounts of brown ash. lent views of the ac tive lava lake. The smaller pit NE of the Ob ser va tions of Niri Mbwelesu. During the 6 Sep tem- lava lake con tained a small lava pond with a di am eter of ber over flight, the pit of Niri Mbwelesu crater was filled ~ 8-10 m. with white vapor. The crater was climbed on 8 Sep tem ber Ob ser va tions of Marum. Two ar eas of fumarolic activ - and obser va ti ons from the S rim showed the crater still ity were seen at the edge of the 1953 crater (be tween filled with vapor; no sounds were heard. During that eve- Marum and Mbwelesu). Brown ash was being emit ted from ning, an orange glow was observe d. Excel lent visi bil ity on the ground at these loca ti ons. 10 Sep tem ber en abled sight ing of a 10-m-di am e ter, crusted In for ma tion Con tact: John Seach, PO Box 4025, Port lava pond. Red lava was visi ble through surface cracks, and Vila, Vanuatu (Email: [email protected], URL: lava spat ter rose 10 m above them at infrequent intervals. http://www.volcanolive.com/). Loud cannon-li ke explo sions about every 20 minutes shook the ground and were accom panied by the sounds of cracking rock. During the eve ning, glowing projec ti les were ejected into the air, although none fell outside the crater. Loud, roaring degas sing noises like a jet engine at take-off were also heard. The roar would gain inten sit y over 30 seconds, cease for 15 sec onds and then re-start. During peri ods of intens e roaring, red lava was observe d through cracks in the crusted surface. Both types of intens e degas sing were ac com panied by gentl e emissions of brown vapor. A pit, 6 m in di am eter , lo- cated N of the crusted pond in the crater wall, emit ted brown ash. Fumaroles were high on the N inner crater wall. Brown ash was emitted from the S crater floor. Ob ser va tions of Mbwelesu. Mbwelesu crater was ob- served for 3 hours during mid-day on 8 Sep tem ber from a po si tion on the SW rim. At times, the crater was filled with Fig ure 4. Lava lake in side Mbwelesu crater at Ambrym on 10 Sep tem ber vapor, but obser va ti on of the lake surface was only possi ble 2003. Sur face crusting and degas sing are clear, note new crater at top of about 60% of the time. The lava lake showed re markable photo. Cour tesy of John Seach. 12 Momotombo Smithsonian Institution — Bulletin of the Global

with a frequency of 7.5 Hz in both July and August. Seis- Momotombo micity in creased in Au gust with a small seis mic clus ter and 176 reg is tered earth quakes, mainly vol cano-tec tonic. The Nic a ra gua major it y of the ac tivit y took place on 1 and 2 August, in- 12.422°N, 86.540°W; sum mit elev. 1,297 m cluding one event felt by staff at the geother mal plant. Seis- mic ity dropped dra mat i cally in Sep tem ber, Oc to ber, and Instituto Nicaraguense de Estudios Territoriales Novem ber, with 7 and 12 vol cano-tectoni c events in Sep- (INETER) re ports from March 2002 through Septem ber tem ber and Oc tober, re spec tively, and none in Novem ber. 2003 in di cate that seism icity has gen er ally been low. Oc ca - Visit s were made on 19, 20, 21, and 22 Novem ber for gas sional visit s to the sum mit of Momotombo (figure 5) are sam pling and tem per a ture mea sure ments. Temper a tures made to sample gases and take temper ature measurements. were measured in 12 fumaroles and around the seism ic sta- The first visit during this time period was on 13 April tions at the base of the volcano. The highest tem pera ture s 2002. Temper ature measure ments in the crater fumaroles were found at fumaroles 3, 4, 5, 8, and 9, with the maxi - showed lit tle vari a tion from pre vi ous mea sure ments, ex cept mum tem pera ture of 768°C at fumarole 9. Tem pera ture s at for fumarole 14, which showed an increa se from 434 to the three fumaroles around the seism ic stati on were 89.9°C, 583°C. There were no visit s in May; seism ic moni tor ing re - 99.1°C, and 90.2°C. corded only one earthquake. Seis micity increased again in De cem ber 2002 and Jan u - Seism icit y increa sed during the early part of June, with ary 2003. A seism ic cluster of 88 events was recorded dur- a seism ic cluster from 1 to 11 June SW of Momotombo ing 24-25 De cem ber. Loca ti ons deter mined for 18 of the consis ting of more than 120 earthquakes . Thirty of these eventsput them all very close to the volcano. In Janu ary 55 earthquakes occurred on 9 June. An event on 8 June was tec tonic earth quakes were reg is tered. Af ter Jan u ary, seis- felt at the geother mal plant W of the volcano. The major it y micit y dropped consid er ably . No earthquakes were regis - of these events were volcano- tectonic earth quakes with fre - tered in Febru ary , and only one was recorded in March. quencie s betwee n 15 and 20 Hz. The unusual tornillos Site vis its in Febru ary include d walking around the (screw-type events) have conti nued to oc cur at crater; no morpho log i cal changes were observe d. The visit Momotombo, usuall y last ing 2-5 seconds with a dominant also in cluded gas sam pling and tem per a ture mea sure ments. frequency of 5 Hz. Fumaroles 8 and 9 measured 759°C and 762°C, respec - Only 16 earthquakes were re corded in July, four of tively; more moni tor ing on 8 and 27 March showed that them on 12 July; none were locat ed. Tornillos conti nued temper a tu res were staying rela tiv ely constant. No visits were made in April, May, or June, but seis mic mon i tor ing con tin ued. Although only one volcano-t ec- tonic earth quake reg is tered in April, tornillos con tin ued, with frequen cie s above 12 Hz. There were 35 vol cano-tectoni c events in May, includ ing a three-hour-long clus ter on 30 May. Six seis mic events reg is- tered in June. A visit was made to the vol- cano on 12 July 2003; tem pera - tures were sim ilar to the pre vi ous months, ranging from 243°C at fumarole 13 to 737°C at fumarole 9. Two earthquakes regis ter ed in Au gust; seis mic ity stayed low through Sep tem ber. Back ground. Momotombo is a young, 1297-m-high stratovolcano that rises prom i- nently above the NW shore of Lake Managua, form ing one of Nic a ra gua’s most fa mil iar land- marks. Momotombo began grow- ing about 4500 years ago at the SE end of the Marrabios Range and consis ts of a somma from an older edi fic e that is surm ounted by a sym met ri cal youn ger cone with a 150 x 250 m wide sum mit crater. Young lava flows from Figure 5. Photo graph of Momotombo (unknown date) showing the E flank and the 1905 lava flows. Note that a Momotombo have flowed down small steam plume is rising from the crater fumaroles. Lake Managua is in the background. Courtesy of INETER. the NW flank into the 4-km-wide Volcanism Network, Volume 28, Number 9, September 2003 Concepcíon 13

Monte Galán cal dera. The youthful cone of Momotombito Num ber of Month Notes forms a 391-m-high island offshore in Lake Managua. earth quakes Momotombo has a long re cord of strombolian erupti ons, punc tu ated by oc ca sional larger ex plo sive ac tiv ity. The lat - Feb 2002 24 est erupti on, in 1905, produced a lava flow that travele d Mar 2002 9 from the sum mit to the lower NE base. A small black plume Apr 2002 1,433 Most activ ity on 5, 9, and 10 April. was seen above the crater af ter an April 10, 1996 earth- May 2002 346 Total of 76 earth quakes on 19 May; quake, but later obser va ti ons noted no signif i cant changes tech ni cal prob lems may have in the crater. A major geo ther mal field is located on the S low ered num ber. flank of the volcano. Jun 2002 865 In for ma tion Con tact: Martha Navarro, Emilio Jul 2002 1,229 Talavera, and Vir ginia Tenorio, Instituto Nicaraguense de Aug 2002 1,219 Most activ ity on 29 and 30 August. Estudios Territoriales (INETER), Dirección Gen eral de Sep 2002 1,250 Most activ ity on 26-27 Septem ber; Geofísica, Apartado Postal 2110, Managua, Nic ara gua no records 1-2 Septem ber. (Email: [email protected]; URL: http://www.ineter. Oct 2002 1,031 Ten days worth of records; most gob.ni/geofisica). activ ity on 28 and 31 Octo ber. Nov 2002 784 Most activ ity on 1 and 2 Novem ber. Dec 2002 389 Jan 2003 179 Miss ing four days of record ings. Concepcíon Feb 2003 108 Nic a ra gua Mar 2003 700 Higher am plitude events re corded 11.538°N, 85.622°W; sum mit elev. 1,700 m betwee n 2 and 18 March. Apr 2003 1,400 Ma jor ity re corded af ter 11 April. Reports from March 2002 through Septem ber 2003 May 2003 476 were provided by Instituto Nicaraguense de Estudios Jun 2003 1,298 Territoriales (INETER). Ac tiv ity has been gen er ally con- Jul 2003 > 1,100 Miss ing three days of record ings. stant from 2001 through 2003, with tremor and very low Aug 2003 1,586 magni tude earthquakes , usuall y detec ted by the stati on on Sep 2003 828 Most activ ity on 12-13 Sep tem ber. the N side of the volcano (CONN). Throughout the sum- Table 6. Monthly count of earthquakes regis ter ed at Concepcion, mary pe riod, there were oc ca sion ally tech ni cal dif fi cul ties Feb ru ary 2002-Sep tem ber 2003. Cour tesy of INETER. at the Mombacho stati on, so no ac tivit y was regis ter ed on those days. Peri ods of noti ceably high seism icit y occurred 149 on 26 Septem ber and 152 on 27 Septem ber. In Oc tober, betwee n June and Octo ber 2002, in April 2003, and during tech ni cal prob lems pre vented re cord ings un til af ter 21 Oc- June-August 2003 (table 6). tober. However, in those ten days 1,031 microearthquakes Seismic ity betw een April 2002 and Febru ary 2003. In regis ter ed, with 161 and 172 on 28 and 31 Octo ber, re spec - April 2002 there were 1,433 microearthquakes detec ted, a tively. Both CONN and URBN de tected lahars on the N signif i cant increa se over the total of 33 recorded during flank on 28 and 31 Octo ber, during a time of moder ate rain - Feb ru ary-March; the major ity of the seis micity was re- fall. Ac tivit y de clined in Novem ber, although 784 earth- corded on 5, 9, and 10 April. The major it y of acti vit y was quakes were still recorded. Acti vit y was highest on 1 and 2 classi fie d as long-period (LP) events with fre quencie s be- November, with 115 and 129 earthquakes respectively. tween 1 and 4 Hz; some events re lated to rock frac turing Ac tiv ity de clined fur ther in De cem ber, with 389 had frequen cie s betwee n 8 and 10 Hz. Acti vit y in May was microearthquakes, al though no re cordings were obtai ned sim ilar , with low-magni tude earthquakes and tremor. How- on five days due to techni cal problem s. Sim ilar to the past ever, due to problem s with CONN, only 346 earthquakes sev eral months, ac tiv ity was classi fied as gen er ally LP or were de tected. On the day of the highest acti vit y, 19 May, degas sing events. Only 179 microearthquakes were re- 76 microearthquakes were re corded. One earthquake, only corded in Janu ary (data was not re ceived on four days). In recorded at CONN, occurred on 28 May with an S-P time Febru ary , only 108 microearthquakes were de tected. All differ ence of 0.8 sec onds, suggesting the hypocenter was at events ranged betwee n 1.5 and 3.5 Hz frequency and were ~ 6.4 km depth. classi fied as LP or degassing events. June-Au gust ac tiv ity was con sis tent with pre vi ous Seismic ity betw een March and June 2003. Be gin ning months. June re corded 865 microearthquakes, while July in March 2003 and conti nu ing through April and May, ac- recorded 1,229 events, mostly early in the month. CONN tivit y increa sed to unusual levels . Be tween 2 and 18 March reg is tered 1,219 earth quakes in Au gust. Seis mic ity was CONN regis ter ed a serie s of 31 earthquakes with consid er - heavi est on 29 and 30 August, with 116 and 139 earth- able ampli tude; they were not felt by res idents in the area. quakes, re spec tively. The earth quakes were clas sified as Because the sta tions at Urbaite (URBN) and Maderas mainly LP. On 4 August an earthquake of M 2.7 occurred (MADN) were not working, only CONN recorded the ac- ~ 15 km S of the volcano at a depth of 12.5 km. On 14 Au- tiv ity. How ever, the dif fer ence in ar rival times be tween the gust an other seis mic station (URBN) was in stalled around S and P waves indi cat ed a depth of 15-16 km. The seis mic Concepcion, this one in the com munit y of Urbaite, on the S signals began at low fre quencie s, fol lowed by an increa se in flank. the spectral frequency content. In Sep tem ber ac tiv ity lev els were again gen er ally sta ble. On 19 March the volcano enter ed a new period of in- Recep ti on problem s conti nued but by 2 Septem ber the sig - creased acti vit y. By the end of March more than 700 events nal was re es tab lished. There were 1,250 earth quakes re- were regis ter ed by the seis mic stati on. Although during the corded, the major it y at the end of the month, with highs of first week of April very few earth quakes were recorded, by 14 Arenal Smithsonian Institution — Bulletin of the Global

11 April the stati on began to regis ter a se ries of earthquakes cano have produced chains of spat ter cones, cinder cones, of con sid er able am pli tude, sim i lar to the se ries in March. lava domes, and maars lo cated on the NW, NE, SE, and More than 1,400 events were recorded, mainly LP events. southern sides extend ing in some cases down to Lake Nica - Only 476 events were recorded in May, also mainly LP ra gua. Concepción was construc ted above a basem ent of events. A total of 1,298 events were recorded in June. lake sedi m ents, and the modern cone grew above a largely Seis mic ity be tween July and Sep tem ber 2003. Un usual bur ied cal dera, a small rem nant of which forms a break in seis mic ac tiv ity, in clud ing har monic tremor that be gan at slope about halfway up the north flank. Fre quent explo sive the end of June, conti nued in July. Starting 1 July, CONN erupti ons during the past half century have increa sed the be gan to reg ister a se ries of LP events ac compa nied by height of the sum mit signif i cant ly above that shown on cur- low-fre quency har monic tremor and a satu rated seis mic sig - rent topo graphi c maps and have kept the upper part of the nal like the one that oc curred in March. Har monic tremor volcano unvegetated. occurred throughout July, with epi sodes of 7 minutes on 2 In for ma tion Con tact: Emilio Talavera, Instituto July, 45 minutes on 4 July, and about 60 minutes on 13 Nicaraguense de Estudios Territoriales (INETER), July. Long-period earthquakes and harm onic tremor in- Dirección Gen eral de Geofísica, Apartado Postal 2110, creased be tween 23 July and the end of the month. Managua, Nic a ra gua (URL: http://www.ineter.gob.ni/ A total of 43 earthquakes with sat urat ed am pli tudes geofisica). were regis ter ed only by CONN in July, but it was not possi - ble to deter mine loca ti ons or magni tudes . The time dif fer- ence in the S-P arriv als im plied hypocenters 15-16 km be- neath the vol cano. They lasted a lit tle over a minute and had Arenal a com bina ti on of high and low fre quencie s. The earth- quakes with sat urat ed signals had frequen cie s of 2-4 Hz; Costa Rica some were accom panied by a low-energy high-fre quency 10.463°N, 84.703°W; sum mit elev. 1,657 m signal. The major it y of these events (7) occurred on 15 and All times are lo cal (= UTC - 6 hours) 16 July, and had ceased by 23 July. Taking the spectra l con- tent into account, these appear to be LP events; however, it On 5 Septem ber the Observatorio Vulcanologico y is not very com mon for LP events to begin with low fre- Sismologico de Costa Rica (OVSICORI-UNA) reported quencie s followed by high. No data were recorded on 18, that a new se quence of pyroclastic flows started at 1055 21, and 22 July due to techni cal problem s at Mombacho, that day (fig ure 6). At least eight sig nals re lated to the col - but a total of more than 1,100 earthquakes were recorded by lapses were recorded within the next two hours by seism o - seismic stations. graphs at the obser va tory . Ma teria l shed from high-ele va - With 1,586 earthquakes regis ter ed, seism icit y was un- tion accu m ula ti ons of lava gener ate d the pyroclastic flows, usuall y high in August. Harm onic tremor also increa sed. which desce nded the N and NE flanks down to 800 m ele - Starting 1 August, CONN began to regis ter a se ries of LP vati on; ac com pany ing ash drifted W and NW. No inju ries earth quakes ac com pa nied by low-fre quency har monic or deaths oc curred, and the main ef fects were limited to tremor and earthquakes with sat urat ed signals , as in previ - within the Nati onal Park boundari es. Patches of vege ta ti on ous months. Frequency ranged from 1 to 2.5 Hz, with occa - at the flow ter mina tions caught on fire. Simi lar flows have sionall y higher val ues. On 16 August trem ors were regis - occurred in recent years (e.g. May 1998, August 2000, and tered that lasted for four minutes ; on 22 August, after two days with no tremor and few earthquakes , there was more un usual ac tiv ity consis ting of seven hours of intermittent tremor episodes. Seis mic ity con tin ued in Sep- tem ber with 828 total events, the major it y on 12 and 13 Septem ber. Seis mic tremor was pres ent through out Sep tem ber, with fre- quency levels sim ilar to those of the previous months. Back ground. Volcán Concepción is one of Nic ara gua’s highest and most acti ve volca - noes. The sym met ri cal stratovolcano forms the NW half of the dumbbell -shaped island of Ometepe in Lake Nic ara gua and is connect ed to neighbor ing Madera vol cano by a narrow isth- mus. A steep-walled summ it crater is 250 m deep and has a higher western rim. N-S-trending Figure 6. Photo graph of a pyroclastic flow descend ing the NE flank of Arenal, 5 Septem ber 2003. Courtesy of fracture s on the flanks of the vol- OVSICORI-UNA. Volcanism Network, Volume 28, Number 9, September 2003 Poás 15

March 2001) affect ing the sum mit and upper areas of the In for ma tion Con tacts: E. Fernández, E. Duarte, E. acti ve cone C. No explo sive erupti ons or extra ordi nary Malavassi, R. Sáenz, V. Barboza, R. Van der Laat, T. Ma - seis mic activity were associated with these latest rino, E. Hernández, and F. Chavarría, Observatorio pyroclastic flows. Vulcanológico y Sismológico de Costa Rica Un re ported ob ser va tions from 2002. At the time of the (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa last sum mary report about Arenal (Bul le tin v. 28, no. 8), in- Rica (URL: http://www.una.ac.cr/ovsi/). form ati on from Janu ary , Febru ary , and April 2002 was not avail able; those OVSICORI-UNA re ports have since been locat ed. Both seism ic and volca nic acti vit y were low during those months, without signif i cant pyroclastic flows or ener - Poás getic erupti ons. Pyroclastic flows from other months that had been descri bed in that and other reports all origi nate d Costa Rica from failures along the margins of lava flows, rather than 10.20°N, 84.233°W; sum mit elev. 2,708 m stem ming from explosive eruptive processes. Back ground. Arenal is the youngest stratovolcano in This report concerns Poás dur ing the in ter val Sep tem ber Costa Rica and one of its most acti ve. The 1657-m-high 2001 through De cem ber 2002. It draws on both a set of ex - andesitic vol cano towers above the eastern shores of Lake tensive half-year reports from UCR-ICE (Mora, 2001a, b; Arenal, which has been en larged by a hydro electric pro ject. 2002) and monthly OVSICORI-UNA re ports (avail able on The earli est known erupti ons of Arenal took place about the web, and someti mes pre pared with co-authors Or lando 7000 years ago. Growth of Arenal has been char acter ized Vaselli and Franco Tassi). OVSICORI-UNA reports were by pe ri odic ma jor ex plo sive erup tions at sev eral-hun- absent for Novem ber and December 2001. dred-year inter vals and peri ods of lava effu sion that arm or Poás was non-erupti ve during the report ing inter val. the cone. Arenal’s most re cent erupti ve period be gan with a The vol cano was last re ported on in Bul le tin (v. 26, no. 11); ma jor ex plo sive erup tion in 1968. Con tin u ous ex plo sive ac- the key fo cus of activ ity rem ains the main crater and its tivit y ac com panied by slow lava effu sion and the oc ca- fumaroles, and its low-pH, vari ably colored lake. That lake sional emission of pyroclastic flows has occurred since then is sometim es called Laguna Caliente or el Poás, but more from vents at the summit and on the upper western flank. frequentl y in past issues of the Bul le tin simply de scribed with terms like the ac tive lake, lake in the ac tive crater, hot lake, etc. Dur ing the re port ing in ter val the ac tive lake re peat edly changed pH, color, and tem pera - ture. As in the past, Laguna Caliente con tained some ther- mally active zones, sometim es dis play ing up-welling wa ter, bub - bles, and zones of nati ve sul fur. Lake Botos lies in a crater S of the active one. It remained inactive. The or i gin and ter mi nol ogy for the main crater’s dome or pyroclastic cone re mains con tro- versia l; both terms are used in this report, congru ent with those fa- vored by the authors of sum ma- rized reports and include d photos. Whatever its name or ori gin, this fea ture sup ports es pe cially ac tive fumaroles, and is fre quently masked by steam. Ob serv ers at the crater noted acous ti cal noise from vig or ous de gas sing. Again, as typ i cal, monthly re ports con sis tently men- tioned vari able sec ond ary fumarolic ac tiv ity and oc ca sional mass-wast ing along the crater walls. Seis mic ity, in clud ing tremor, conti nued and is men- Figure 7. A verti cal or sub-ver tical aeria l photo taken of the sum mit at Poás, with N to ward the bot tom left. tioned be low, but it will be dis- Num bers on the photo refer to lo cations named on the key. As an approx i m ate scale, the lake is ~ 200-300 m in diam eter . This was taken from figures in Mora (2001a and b, and 2002) that had severa l other photos around the cussed more com pre hen sively in mar gin. Construc tion lines origi nally across this photo have been re moved here, with some re sulting loss and a later report. local misrep re sen ta tion of what must have been present on the origi nal photo. Courtesy of UCR-ICE (after Mora UCR-ICE ob ser va tions. Mora 2001b and 2002). (2001b and 2002) include d an 16 Poás Smithsonian Institution — Bulletin of the Global overview photo of Poás (figure 7). Those re ports also in- cluded num erous other photos of fumaroles and mass wast - ing, most of which are not shown here. Some pronounced ar cu ate cracks as so ciated with mass wast ing along the NE side of the lake were thought possi bly relat ed to changes in lake level and pore pres sure (figure 8). A shot of the steam - ing dome appears as figure 9. Mora (2001a, b and 2002) col lected and present ed con- sid er able data on Laguna Caliente, and we in clude sev eral available plots. Lake tem pera ture and pH during 2001-2 ap - pears as figure 10; precip i ta ti on and lake level for most of 2002, as figure 11. Mora (2002) re ported March-De cem ber 2002 pre cip i ta- tion ranging from 33 to 607 mm per month (figure 11). The lake’s vari able sur face heights dur ing March-De cem ber 2002 de vi ated from an es tab lished (ar bi trary) da tum (zero point), from which heights ranged from ~ 400 mm below the da tum to ~ 100 mm above it. During this inter val the Figure 10. For Laguna Caliente at Poás, plots show ing tem per a ture and pH ver sus month during (top) 2001 and (bottom ) 2002. The var ious scales lake’s high stand oc curred in Decem ber; it then covered the are un equal. The two-year peak tem per ature measured 41.5°C in border of the low est N ter race. The lowest stand for the in- Septem ber 2002. The lowest pH measured ~ 0 during March-Octo ber ter val oc curred dur ing May. During this time inter val the 2001 and during Janu ary , July, and August 2002. (After Mora, 2001b and 2002).

Figure 11. For Laguna Caliente at Poás, a plot show ing pre cip i ta tion and lake-surface level versus month during March-Decem ber 2002. The lo ca tion where the pre cip i ta tion mea sure ments were taken was un stated. Values shown on the plot are in milli m eter s (After Mora, 2002).

vari ables of precip i ta ti on and lake height appeared to lack consistent correlation. Figure 8. Laguna Caliente, the hot lake at Poás (lower right) lies within a OVSICORI-UNA ob ser va tions. During late 2001 and crater bounded by unsta ble cliffs. This photo shows part of the lake’s NE through 2002, low-frequency earthquakes conti nued to mar gin. The per son in this scene stands on a substan tial though eroding dom inate the re cord, with OVSICORI-UNA re porting terrace and in spects ar cu ate cracks (cir cumfer ential faults) in un sta ble mate rial along the crater rim. Some of these cracks reached 40 cm wide. ~ 500 events per day on 8 Septem ber, but more typi cal ly Landslide depos its from failures along this and other cliff faces were 100-300 events per day. In addi ti on during this inter val in - mentioned frequently in re ports. Courtesy of UCR-ICE (from Mora strum ents typi cal ly recorded several hours of tremor per 2001a). month. During some months of the report ing inter val, me- dium- and high-frequency earthquakes conti nued to oc cur in conjunc ti on with new fumaroles appearing in the active crater. The OVSICORI-UNA re port dis cuss ing Sep tem ber 2002 noted that tremor rose slightly, pre vail ing for ~ 5 hours on each of several days. Long-period earthquakes num bered more than 100 per day, and typi cal ly 300-450 per day. Medium -frequency earthquakes occurred much less often, their num bers approach ing ~ 20 per day on several days, and more typi cal ly fewer than 10 per day. During the last half of 2002 the lake’s wa ter tem pera - ture rose above 30°C, at taining 39°C during Septem ber-De- cem ber 2002. Low ered air tem pera ture s in late 2002, par- ticu lar ly in Novem ber 2002, led to conden sat e form ing over the lake’s sur face and ris ing to ac cu mu late in larger, op ti- Fig ure 9. The N face of the dome (or pyroclastic cone) at Poás rises from cally dense clouds (figure 12). the lake and supports strong fumaroles. This photo was taken looking S. Ref er ences: Mora, R., 2002, Informe anual de la Scien tists par tially vis ible atop the dome were walking to fumaroles where they measured gas tem per atures and pH. Cour tesy of UCR-ICE actividad de la Cor dil lera Volcánica Centra l, 2002, Costa (from Mora, 2001). Rica (proofed and revise d by Alvarado, G., Fernández, M., Volcanism Network, Volume 28, Number 9, September 2003 Poás 17

Mora, M., Paniagua S., and Ramírez, C.): Universidad de Costa Rica, Red Sismológica Nacional, UCR-ICE, Sección de Sismología, Vulcanologíay Exploración Geofísica (publi shed June 2003 as mini-CD Rom with PDF files). Mora, R., 2001a, Informe semestral de la actividad de la Cor dil lera Volcánica Cen tral, Enero-Junio 2001, Costa Rica: Universidad de Costa Rica, Red Sismológica Nacional, UCR-ICE, Sección de Sismología, Vulcanologíay Exploración Geofísica (pub lished No vem ber 2001 as mini-CD Rom with PDF files). Mora, R., 2001b, Informe semestral de la actividad de la Figure 12. Conspic u ous conden sate hung over the active crater lake at Poás during late 2002. The conden sate Cor dil lera Volcánica Cen tral, stemmed from warm lake tem per atures (~ 39°C) com bined with cooler am bi ent air tem per atures. At the time of Julio-Diciembre 2001, Costa Rica this photo (Novem ber 2002) the lake was light green in color. Cour tesy of OVSICORI-UNA. (proofed and revise d by Alvarado, G., Fernández, M., Montero, W., and Ramírez, C.): Universidad de Costa Rica, Red Sismológica Nacional, UCR-ICE, Sección de Sismología, Fumarolic ac tiv ity and Month Lake-wa ter color Vulcanologíay Exploración OVSICORI-UNA’s comm ents. Geofísica (publi shed 6 May 2001 as mini-CD Rom with PDF files). Sep 2001 Turquoise, with centra l lake High est re corded tem per a tures, 92-110°C. Back ground. The broad, con vec tion cells of cof fee color well-veg e tated ed i fice of Poás, Oct 2001 Tur quoise Loud noises at pyroclastic cone, where es cap ing gases contin ued to be most plen tiful and vigor ous; these had one of the most acti ve volca noes mea sured tem per a tures of 91°C at an ac ces si ble spot. of Costa Rica, con tains three crat- High est re corded tem per a tures, 92-110°C. ers along a N-S line. The fre- Nov 2001 n.a. quently visit ed multi-hued sum- Dec 2001 n.a. mit crater lakes of the vol cano, Jan 2002 Dark green Pyroclastic cone vapor emissions rose to 200 m. which is one of Costa Rica’s most Max i mum fumarole tem per a tures mea sured 85-91°C. prom i nent nat u ral land marks, are Feb 2002 Blue Cone vapor emissions rose to 200 m; maxi m um fumarole eas ily ac ces si ble by ve hi cle from tem per a tures mea sured 90-100°C. the nearby cap ital city of San Mar 2002 Clear blue Cone’s vapor emissions rose to 300 m; maxi m um tem per a tures reached 93-98°C. José. A N-S-trending fissure cut- Apr 2002 Celeste (a gray ish blue to pale 300 m; 93-99°C. ting the 2,708-m-high com plex pur plish blue) stratovolcano extends to the lower May 2002 Tur quoise Noisy, audi ble from northern crater margin; 97-107°C; northern flank, where it has pro- new fumaroles ap peared. duced the Congo stratovolcano Jun 2002 Turquoise- green to celeste Prom i nent cracks cross ing lake terrace; new fumaroles and sev eral lake-filled maars. The appear ed but had low gas flux rates. southern m ost of the two sum mit Jul 2002 Turquoise to celeste 300-400 m high; 119°C; sulfur depo si tion. crater lakes, Botos, is cold and Aug 2002 Turquoise to celeste 300 m high; new bubbling notice d at lake’s center and S clear and last erupted about 7,500 mar gin; max i mum re ported tem per a ture, 119°C. years ago. The more prom inent Sep 2002 Turquoise to celeste 119°C. geothermally heated northern lake Oct 2002 Turquoise to celeste Noisy; 400 m high; sul fur depo sition; low gas fluxes; is one of the world’s most acidic max i mum tem per a ture, 130°C. natu ral lakes, with a pH of near Nov 2002 Turquoise to celeste A com par atively warm lake sur face and cooler air tem per a tures led to con spic u ous clouds form ing over the zero. It has been the site of fre- lake sur face. A max i mum tem per ature was seen at a N quent phreatic and phreato-mag- terrace fumarole (122°C). matic erup tions since the first his - Dec 2002 Tur quoise Max temp 119°C. tor i cal erup tion was re ported in Table 7. For the active crater at Poás, a sum mary on lake-water color and visi ble and therm al obser va tions dur ing 1828. Poás erupti ons often in- the inter val Sep tem ber 2001 through De cem ber 2002. The fumarolic ac tivity typi call y refers to outgassing at the clude geyser-like ejection of pyroclastic cone (dome). Miss ing data is indi cate d by n.a. (not available) . The source reports excluded the exact crater lake water. dates and detail s descri b ing the collec tion of these obser va tions. Courtesy of OVSICORI-UNA. 18 Barva Smithsonian Institution — Bulletin of the Global

In for ma tion Con tacts: R. Mora (Amador), C. Ramírez, Satellitic cones are found on the northern and southern and M. Fernández, Universidad de Costa Rica, Laboratorio flanks. Lava flows blanket the south side of Barva vol cano. de Sismologia, Vulcanología y Exploración Geofisica, The Los Angele s flow, one the most re cent, desce nds Aptdo. 560-2300, Curridabat, San José, Costa Rica (Email: nearly to the city of Heredia. A large plinian erupti on oc- [email protected]); E. Fernández, E. Duarte, E. curred at Barva during the early Holo cene . Erupti ons were Malavassi, R. Sáenz, V. Barboza, R. Van der Laat, T. Ma - reporte d in 1760 or 1766, 1776? (also a mudflow), and rino, E. Hernández, and F. Chavarría, Observatorio 1867, but later visit s to the sum mit did not provide evidence Vulcanológico y Sismológico de Costa Rica of eruptions during historical time. (OVSICORI-UNA); Jorge Barquero and Wendy Sáenz, In for ma tion Con tacts: Raul Mora Amador, Red Laboratorio de Química de la Atmósfera (LAQAT), Depto. Sismologica Nacional, Laboratorio de Sismologia, de Química, Universidad Nacional, Heredia, Costa Rica; Vulcanologia y Exploracion Geofisica, Universidad de María Martínez (at both af fil i a tions above), Orlando Costa Rica, Apartado 214 (2060) UCR, San Jose, Costa Vaselli and Franco Tassi, De part ment of Earth Sci ences, Rica (Email: [email protected], URL: Univer sit y of Florence , Via La Pira 4, 50121 Florence , http://www.rsn.geologia.ucr.ac.cr/). It aly.

Nyamuragira Barva DR Congo, centra l Afric a Costa Rica 1.408°S, 29.20°E; sum mit elev. 3,058 m 10.135°N, 84.10°W; sum mit elev. 2906 m The last erupti on at Nyamuragira occurred dur ing 25 Ge ol o gist Raul Mora, along with Carlos Ramirez and July-27 Septem ber 2002 (Bul le tin v. 27, nos. 7 and 10, and Maritta Alvarado, visit ed Barva vol cano during De cem ber v. 28, no. 1). Tectoni c and magm atic seism icit y conti nued 2002 and inves ti gated the Barva and Copey crater lakes. through June 2003, but there has been no confirm ed erup- Lo cated in a small crater, the Barva crater lake (fig ure 13) tive ac tiv ity. This re port cov ers ac tiv ity from early July to was very clear; at 5 m from the shore the wa ter had a tem- the be gin ning of Au gust 2003. Seis mic ity gen er ally con- pera ture of 11-12°C with a pH of 4-5. Water in the Copey sisted of long-pe riod (LP) earthquakes on the NE side of lake was amber colored and very cloudy, with a temper a- the vol cano. In addi ti on, earthquake swarms were occa sion - ture at 0.5 m depth of 12.2°C and a pH of 5. Near-surface ally observe d. black lapilli depos it s were found that were more than a me- Betwee n 6 and 12 July, seis micit y was dom inate d by LP ter thick near the Barva lake, but be came more ir reg u lar in earthquakes NE of the volcano and SE along the fracture thickness around the Copey lake. zone be tween Nyamuragira and Nyiragongo. Two large Back ground. The centra l and least known of three mas- swarms occurred on 7 and 8 July, with 161 LP earthquakes sive volca noes tower ing over the capi tal city of San José, and 10 short-period earthquakes . The earthquakes at Volcán Barva (Barba) is a com plex vol cano with multi ple Nyamuragira have been deep, betwee n 15 and 20 km. sum mit and flank vents. Its three princi pal sum mits vis ible During 13-19 July 2003, LP earthquakes NE of the vol- from the Cen tral Val ley give it the common lo cal name of cano again dom inate d seism icit y. Com pared to the previ ous Las Tres Marías. The vo lu mi nous Tiribí Tuff, exposed in week, acti vit y was low, with no swarms and only one the Cen tral Val ley of Costa Rica, was erupted about high-fre quency earthquake. The fol lowing week, betwee n 330,000 years ago from the Barva sum mit cal dera. Four 20 and 26 July, LP earthquakes conti nued in the NE and to pyroclastic cones are construc ted within the 2 x 3 km cal- a lesser ex tent along the SE fracture zone. Be tween 19 and dera at the cen tral and NW part of the summ it. The SW 21 July new se quences of earthquakes occurred, with LP peak contai ns four cones, one of which has a crater lake. events followed by short-period earthquakes , coupled with high-am pli tude tremor episodes. Betwee n 27 July and 2 August, LP earthquakes conti n - ued to dom inate seism icit y NE of the vol cano as well as along the SE frac ture zone. Seis micity increased from the previ ous week, with sequence s of LP earthquakes coupled with volca nic tremor epi sodes be tween 28 and 31 July. Av- erage seis micit y doubled to 200 earthquakes with hypocenters betwee n 3 and 20 km deep. Back ground. Af rica’s most active vol cano, Nyamuragira is a massive ba saltic shield vol cano that rises about 25 km north of Lake Kivu across a broad valley NW of Nyiragongo vol cano. Nyamuragira has a volum e of 500 cu km, and exten sive lava flows from the vol cano blanket 1500 sq km of the East Afri can Rift. The broad low-angle shield vol cano con trasts dra mati cally with its steep-sided neighbor Nyiragongo. The 3058-m-high sum mit of Nyamuragira is truncat ed by a small 2 x 2.3 km cal dera that Figure 13. Photo graph of the Barva crater lake, Decem ber 2002. The lake has walls up to about 100 m high. Histor i cal erupti ons have has an area of 9,000 m2 and a depth of ~ 7.7 m. Cour tesy of Raul Mora. oc curred within the sum mit cal dera, fre quently mod i fy ing Volcanism Network, Volume 28, Number 9, September 2003 Piton de la Fournaise 19 the morphol ogy of the caldera floor, as well as from the nu- edge of the crater. Because of the con sid er able pro jec tion of merous fis sures and cinder cones on the volcano’s flanks. A volcanic products, pilots were advised to avoid the area. lava lake in the sum mit crater, ac tive since at least 1921, Follow ing a magni tude 5.2 earthquake in the Virunga drained in 1938, at the time of a major flank erupti on. His - region on 5 August, scien ti sts from the Goma obser va tory tori cal lava flows extend down the flanks more than 30 km visit ed Nyiragongo on 14-15 August. Measure m ents in- from the summit, reaching as far as Lake Kivu. cluded de for ma tion and gas geo chem is try in frac tures, and In for ma tion Con tact: Goma Vol cano Ob ser va tory, the lava lake was mon i tored. No sig nif i cant de for ma tion Departement de Geophysique, Cen tre de Re cher che en Sci - was observe d at cracks on the S side of Nyiragongo. Gas ences Naturelles, Lwiro, D.S. Bukavu, DR Congo (Email: measure ments at Shaheru showed that lo cal CO2 con cen tra - [email protected]). tions had increa sed by 1.7%, while methane there had dou - bled. At the top of Nyiragongo, however, measure m ents on 15 August were half those on 14 August. Late on 14 August a “swirl” of air caused gas to fill the crater, and ~ 2 hours Nyiragongo later sci en tists as well as res iden ts west of Virunga felt an earthquake. Another earthquake was felt in Kibati and at DR Congo, centra l Afric a the crater on 15 August. 1.52°S, 29.25°E; sum mit elev. 3,470 m The lava lake appeare d calm on 14 August, and two small vents were visi ble; only one was visi ble the next day. New reports of acti vit y at Nyiragongo include obser va - The lava lake was measured to be 260 m in diam eter, nearly tions from visit s on 12-13 July and 14-15 August 2003. the same as on 2 August. Also during the visit sci enti sts in- Seism icit y was low during the report pe riod, but tremor re- stalled a scorimeter: Two hours worth of scoria , weighing lated to the lava lake con tin ued to char acter ize vol canic ac - 236.2 g per square meter , were sampled. tivit y. Staff at the Goma obser va tory have kept the haz ard Back ground. One of Afric a’s most nota ble vol canoes, sta tus for Nyiragongo at Yellow (Vigilance). Nyiragongo contai ned a lava lake in its deep sum mit crater During 6-12 July two long-pe riod earthquakes were de - that was ac tive for half a cen tury be fore drain ing cat a- tected. Four tectoni c earthquakes regis ter ed to the S and be- strophi cal ly through its outer flanks in 1977. In contra st to neath Lake Kivu; none of these were felt by area res idents. the low profil e of its neighbor ing shield vol cano, Frac ture measure ments at Monigi, Mugara, and the Nyamuragira, 3470-m-high Nyiragongo display s the steep Nyiragongo hut did not show any signif i cant change from slopes of a stratovolcano. Benches in the steep-walled, pre vi ous measure ments, but at Lemera frac ture spacing in - 1.2-km-wide sum mit crater mark lev els of for mer lava creased from 7.537 to 7.550 m, and there was an exten sion lakes, which have been observe d since the late-19th cen- of 8 mm at Shaheru. Also during the visit, Pele’s hair as tury. Two older stratovolcanoes, Baruta and Shaheru, are long as 10-15 cm was observe d betwee n Shaheru and the parti ally overlappe d by Nyiragongo on the north and south. crater; gas plumes were noted in the S, SW, and W, along About 100 para sit ic cones are locat ed pri maril y along radial with large scoriae. Crater obser va ti ons indi cat ed the possi - fissures south of Shaheru, east of the sum mit, and along a ble form ati on of a third platform at 650 m depth. Two small NE-SW zone extend ing as far as Lake Kivu. Many cones vents formed NE of the main lava lake and there was signif - are buried by volu m inous lava flows that extend long dis- icant degas sing along the S base of the internal wall. tances down the flanks of the volcano. The extre mely fluid Betwee n 13 and 19 July, seis mic acti vit y re mained low, 1977 lava flows caused many fatal iti es, as did lava flows with four long-pe riod earthquakes beneat h the NE flank. that inun date d porti ons of the major city of Goma in No earth quakes were felt and only seven tec tonic earth- January 2002. quakes were re corded to the S and beneat h Lake Kivu. Vol - In for ma tion Con tact: Goma Vol cano Ob ser va tory, ca nic tremor per sisted, in di cat ing ac tiv ity in the lava lake. Departement de Geophysique, Cen tre de Re cher che en Sci - Frac ture spacing measure ments were taken at Shaheru and ences Naturelles, Lwiro, D.S. Bukavu, DR Congo (Email: the Nyiragongo hut, but without noti ceable changes [email protected]). (14.778 m at Shaheru 1, 29.602 m at Shaheru 2, and 0.942 m at Nyiragongo hut). Obser va ti ons of fumarole openings had been reporte d by resi dents in the Mutwanga distri ct. Also on 18 July inves ti gati ons at Kiziba reveal ed a re cent Piton de la Fournaise tongue of lava infil trating older lava layers, found in a hole dug as a septic tank. Réun ion Is land, In dian Ocean Volca nic trem ors conti nued betwee n 20 July and 2 Au- 21.23°S, 55.71°E; sum mit elev. 2,631 m gust; no earth quakes were repor ted. Frac ture measure ments All times are lo cal (= UTC + 4 hours) at Busholoza and Kabutembo did not indi cat e signif i cant changes; tem per a ture and de for ma tion mea sure ments at the A seism ic crisis started at 2225 on 30 Septem ber 2003 top of Nyiragongo, the Nyiragongo hut, Shaheru, Mugara, beneat h the SW cor ner of Dolomieu crater ~ 2 km below and Monigi also did not reveal any nota ble changes. How- the sum mit. At 2330 erupti on tremor appeare d and was lo- ever, lo cal CH4 (methane) was pres ent at con cen tra tions of cal ized beneat h the SSW flank of Piton de la Fournaise. A 35.5%. straight 400-m-long fissure opened at 2,350 m ele va ti on. Between 1 and 3 Au gust the lava lake ap peared very ac - The erupti on tremor reached a maxi m um at 0100 on 1 Oc- tive, with lava fountai ns up to 10 m high, project ing large tober and de clined after 0200, dis appear ing completely at but light scoriae into the at mosphere . Pele’s hair was ob- 1300. served at Shaheru (2,200 m ele va ti on) and heat ra diat ing Since March 2003, the extensometer net work and GPS from the lake could be felt at the obser va ti on camp on the mea sure ments had in di cated in fla tion of Pi ton de la 20 Piton de la Fournaise Smithsonian Institution — Bulletin of the Global

Fournaise. A new erupti on that began on 30 May within grown within the youngest cal dera, which is 8 km wide and Dolomieu crater procee ded in multi ple phases through 7 breached to be low sea level on the east ern side. More than July, followed by new acti vit y through 27 August (Bul le tin 150 erupti ons, most of which have produced fluid basal tic v. 28, nos. 5, 6, and 8). lava flows, have oc curred since the 17th century . Only six Back ground. The massive Piton de la Fournaise shield erupti ons, in 1708, 1774, 1776, 1800, 1977, and 1986, have volcano on the French is land of Réunion in the west ern In- origi nate d from fissures on the outer flanks of the caldera. dian Ocean is one of the world’s most acti ve volca noes. The Pi ton de la Fournaise Volcano Obser va tory , one of Much of its >530,000 year history overlappe d with erup- several oper ate d by the Institut de Physique du Globe de tions of the deeply dissec ted Piton des Neiges shield vol- Paris, monitors this very active volcano. cano to the NW. Three calde ras formed at about 250,000, In for ma tion Con tact: Thomas Staudacher, 65,000, and less than 5000 years ago by progres sive east- Observatoire Volcanologique du Piton de la Fournaise ward slumping of the volcano. Num erous pyroclastic cones Institut de Phy sique du Globe de Paris, 97418 La Plaine des dot the floor of the cal deras and their outer flanks. Most his- Cafres, La Réunion, France (URL: http:\\vol- tori cal erupti ons have origi nate d from the sum mit and cano.ipgp.jussieu.fr:8080\re union\stationreu2.html; Email: flanks of Dolomieu, a 400-m-high lava shield that has Thomas.Staudacher@univ-re union.fr).

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