Bul Le Tin of the Global Vol Can Ism Net Work

Home , Gluck (crater), Marti (crater)

Bulle tin of the Global Vol can ism Net work Vol ume 32, Num ber 12, Decem ber 2007

Piton de la Fournaise (Re union Island) Caldera collapse in April 2007; large E-flank lava flows ...... 2

Batu Tara (In do ne sia) Ther mal anom a lies be gin ning Jan u ary 2007; ash plumes dur ing March-Oc to ber ...4

Anatahan (Mariana Is lands) During 2007-8 the crater lake dries up, contin u ing ash clouds ...... 5

Bezymianny (Kamchatka Pen in sula) Cor rec tion to plume de scrip tion in No vem ber 2007...... 7

El Chichón (México) Stable with tremor; hot spring; sig nifi cant crater-lake-volume varia tions ...... 7

Fuego (Gua te mala) Moder ate Strombolian eruptions, includ ing pyroclastic flows, continue into early 2008 ..8

Poás (Costa Rica) Small phreatic eruption from crater lake on 13 Janu ary 2008...... 11

Guagua Pichincha (Ec ua dor) Seven moder ate phreatic eruptions on 1 Febru ary 2008 ...... 12

Ed itors: Rick Wunderman, Ed ward Venzke, and Sally Kuhn Sennert Vol un teer Staff: Rob ert An drews, Hugh Replogle, Mi chael Young, Paul Berger, Jacquelyn Gluck, Margo Morell, Ste phen Bentley, Antonia Book binder, and Jeremy Book binder, Veron ica Bemis, and Ludmila Eichelberger

Global Vol canism Program · National Museum of Natural History, Room E-421, PO Box 37012 · Washing ton, DC 20013-7012 · USA Tele phone: (202) 633-1800 · Fax: (202) 357- 2476 · Email: [email protected] · URL: http://www.vol cano.si.edu/

The text of the Bul le tin is also distrib uted through the Volcano Listserv (vol [email protected]). 2 Piton de la Fournaise Smithsonian Institution — Bulletin of the Global

ically venting at the summit and proxi mal areas. Five dis tal Piton de la Fournaise eruptions occurred during 1998-2007, chiefly concen trated along the NE rift zone, and in partic u lar, on the Plaine des West ern In dian Ocean Osmondes. Pahoehoe lava flows had completely filled 21.231°S, 55.713°E; summit elev. 2,632 m Dolomieu’s floor, ac cu mu lat ing dur ing an Au gust All times are local (= UTC + 4 hours) 2006-Janu ary 2007 eruption to a thickness of 20-30 m. Prelude to collapse. On 26 Febru ary 2007 seismic ity A cal dera collapse oc curred at this massive, dy namic started below the summit zone. It progres sively increased shield vol cano during early April 2007, dis plac ing the 0.8 x and over 100 events took place daily during 28-30 March. 1.1 km floor of the ellip ti cal Dolomieu caldera downward Seismic ity reached anoma lously high levels on 30 March at by ~ 330 m (figure 1). This was both the largest collapse at 2025 local time. About 2.4 hours later, a fissure began this volcano since 1760, and one of the few large collapse erupting at 1,900 m ele va tion SE of Dolomieu and Bory events seen at this volcano. Worldwide, such events are crat ers and the cen tral cone (at the point labeled 1, fig ure 1). rarely doc u mented by eyewit ness or in stru men tal ob ser va- Discharges contin ued for 10 hours. Tremor ceased early the tions, with best known exam ples of collapses includ ing next day. those in 1968 at Fernandina (Simkin and Howard, 1970) The 30-31 March eruption included lava fountains up to and in 2000 at Miyake-jima (Kaneko and others, 2005). 50 m in height feeding volu mi nous lava flows. This event The collapse at this Piton de la Fournaise occurred in as- was the debut of a new phase of volca nism that presaged soci a tion with the early stages of one of the largest histor i - the Dolomieu cal dera collapse seen in April. cal dis charges of lava flows ever seen here. The re sult ing Col lapse. A new eruptive phase began 2 April, venting lavas trav eled E to reach the sea where they built a delta. at ~ 600 m ele va tion ESE of the cen tral cone (at point 2, fig- Con cur rent with col lapse, the seis mic ity and de for ma tion ure 1). The venting took place along a NW-trending, were cy clic in na ture, sug gest ing col lapse pro ceeded in a 1-km-long fissure. step-by-step manner. These and other events are ex plained During the next few days, seis micity rates rose to by in a recent paper by Michon and others (2007), the ~ 3-fold larger than in the previ ous (26 Febru ary) epi sode. source used to compile this report. Our last report, BGVN As seismic ity grew on 5 April, the perma nent GPS instru - 32:01, discussed events through 22 Febru ary 2007. ment SNEG situ ated just NE of Bory crater’s rim (figure 1) Piton de la Fournaise has under gone intense eruptive started to displace inward. The verti cal compo nent of mo- activ ity since 1998, with two to four eruptions per year typ- tion began with a jolt around noon and markedly pro- gressed during 1900-2300. Next, at 0048 the next day, an Md 3.2 earth quake oc curred be low the summit (Bory) crater. After that earth quake, seis mic sta tion Takamaka (Tkr, figure 1) regis - tered a sig nal in crease of ~ 50%. Co in ci dent with the earth quake, the GPS instru ment displaced ~ 15 cm outward. What followed was a se ries of cy clic de for ma tion events, epi sodes composed of displace ments pro gres sively in ward followed by ones sharply out ward. The dis place ments linked closely to a se ries of cy clical seismic and tremor epi sodes. Each of those consisted of a sharp, post col lapse tremor in crease, followed by in ter vals of sta ble tremor. Many of these initial tremor cycles oc curred on roughly two-hour in ter vals (through the first hours of 6 April), but gradu ally (with ap- proach to dawn on 6 April) these cycles occurred at about half-hour inter vals. On 6 April there occurred a parox ys mal phase during Figure 1. Maps taken from Michon and others (2007) showing loca tion and key geog ra phy of Piton de la which 200 m high lava fountains Fournaise volcano on Reunion island. The inset shows the volcano at the island’s E end and indi cates the volcano’s two major NE- and SE-trending rift zones (NERZ and SERZ). The larger map indi cates major features, vented. in clud ing the Bory and Dolomieu crat ers (arrows with heads to re spec tive crater rims), two seis mic sta tions, GPS Tremor descended to initial station SNEG, and key vents in the 30-31 March and April erup tive ep isodes (1, and the main vent, 2). Note the lev els be fore the par ox ys mal scales on the frame indi cate dis tance in ki lo me ters. phase, but cy clical seismic sig nals Volcanism Network, Volume 32, Number 12, December 2007 Piton de la Fournaise 3

Miyakejima Volcano, Japan: Bull. Volcanol., v. 67, p. 243-253, doi: 10.1007/s00445-004-0407-1. Michon, L., Staudacher, T., Ferrazzini, V., Bachélery, P., and Marti, J., 2007, April 2007 collapse of Piton de la Fournaise: A new exam ple of cal dera forma tion: Geo physi - cal Research Letters, v. 34, p. L21301, doi:10.1029/ 2007GL031248,2007. Peltier, A., Staudacher, T., and Bachélery, P., 2007, Constraints on magma transfers and structures involved in the 2003 actity at Piton de La Fournaise from displace ment data: J. Geophys. Res., v. 112, p. B03207, doi: 10.1029/ 2006JB004379.

Figure 2. Lava flows at Piton del la Fournaise during the eruption of 6 April 2007. Cour tesy of OVPF.

remained until 0100 on 7 April. Venting contin ued until 1 May, ac com pa nied then by fluc tu at ing tremor. Es timat ing the vol ume of lava emitted was compli cated by abun dant lava hav ing entered the sea at the coast, where it built a large platform, but based on topog ra phy and bathymetry before and after the event, the authors’ rough esti mate, in millions of cubic meters, was ~ 100-140. This makes this one of the most volu mi nous eruptions at this volcano during the 20th and 21st centu ries (figure 2). Col lapse mor phol ogy and struc ture. The first summit zone obser va tions on the after noon of the 6th (~ 16 hours af ter the be gin ning of the seis mic cycles) re vealed that the pre vi ous geo phys i cal ob ser va tions and in tense erup tions coin cided with cal dera collapse (fig ure 3). The 6 April col - lapse affected the Dolomieu’s N part, descend ing the zone shaded in fig ure 3 (b) along sub-verti cal scarps to the E, N, and W, with a net offset of 200-300 m. The pre-exist ing floor remained intact on the E and S, forming arc-shaped pla teaus there. On 10 April the caldera had enlarged to en gulf most of the Dolomieu struc ture. It had deepened to a maxi mum offset (de ter mined from tri an gu la tion and con firmed with AS- TER stereo images) of 320 to 340 m. Perched plateaus were restricted to the indi cated zones. Subse quent morphologic changes were minor. The post-collapse cal dera had di am e- ters of 800 x 1,100 m and encom passed 82 x 104 m2, an area 11% larger than it was prior to the April eruptions. The au thors es timated that the post-col lapse cal dera’s downward movement displaced a volume of 100-120 million cu bic me ters. This dis place ment was com pa ra ble to their esti mated volume of emitted lava (~ 100-140 million cu bic meters). The ini tial stage of col lapse (seen 6 April; figure 3b) accounted for ~ 80% of the total volume displaced in the offset. The April collapse may have followed pre-exist ing ar- cu ate faults. It may also have de scribed a magma cham ber, the size and loca tion of which were re cently de ter mined from a GPS in version (Peltier and others, 2007). That study suggested a shallow chamber with diam e ters of 1.4 km and Figure 3. Piton de la Fournaise’s Dolomieu caldera depicted in sketch 1.0 km in the respec tive E-W and N-S direc tions. maps both prior to the April 2007 eruption and at two stages during the Ref er ences: Kaneko, T., Yasuda, A., Shimano, T., eruption. The first part (a) repre sents 31 Octo ber 2006. The arrow Nakada, S., and Fujii, T., 2005, Subma rine flank eruption indi cates a fracture network (Carter and others, 2007). Af ter Michon and pre ced ing cal dera sub si dence dur ing the 2000 erup tion of oth ers (2007). 4 Batu Tara Smithsonian Institution — Bulletin of the Global

Simkin, T., and Howard, K. A., 1970, Caldera collapse on 14 March the plume was seen extend ing about 90 km in Galapagos Islands, 1968: Science, v. 169, p. 429-437. NE, af ter which it dis si pated. Later that day the low-level Geo logic Sum mary. The massive Piton de la Fournaise plume was 55 km long towards the ENE. basaltic shield vol cano on the French is land of Réunion in A contin u ous low-level plume, at or below summit the western Indian Ocean is one of the world’s most active level, was observed on im agery on 15 March extend ing SE volca noes. Much of its >530,000 year history overlapped from the summit to a distance of 65 km. The plume later with eruptions of the deeply dissected Piton des Neiges shifted around to wards the E, to a dis tance of ~ 37 km, on shield volcano to the NW. Three calde ras formed at about 16 March. Imag ery on 17 March showed another direc tion 250,000, 65,000, and less than 5000 years ago by progres - change, to the NE, extend ing a maxi mum of 74 km. Gov- sive eastward slumping of the volcano. Numer ous ern ment of fi cials, res i dents, and fish er men on Lembata Is- pyroclastic cones dot the floor of the calde ras and their land (formerly known as Lomblen), ~ 50 km S, observed outer flanks. Most histor i cal eruptions have origi nated from plumes rising from Batu Tara during 17-19 March, but the summit and flanks of Dolomieu, a 400-m-high lava there was no night glow. The plumes on 19 March were re- shield that has grown within the youn gest cal dera, which is portedly 500-1,500 m high and blowing E. Although mete - 8 km wide and breached to below sea level on the eastern o ro log i cal clouds in ter fered with sat el lite ob ser va tions, the side. More than 150 eruptions, most of which have pro- Cen tre of Vol ca nol ogy and Geo log i cal Haz ard Mit i ga tion duced fluid basaltic lava flows, have occurred since the (CVGHM) reported contin u ous eruptions with ash to 500 m 17th century. Only six eruptions, in 1708, 1774, 1776, above the summit on 20 March. A contin u ous thin plume 1800, 1977, and 1986, have orig inated from fissures on the was also seen on satel lite imag ery extend ing 37 km NE on outer flanks of the caldera. The Piton de la Fournaise Vol- 20 March. Simi lar activ ity contin ued through 21-22 March, cano Obser va tory, one of several oper ated by the Institut de with low-level plumes iden ti fied in imag ery out to dis tances Physique du Globe de Paris, moni tors this very active of 46-56 km towards the E and SE. vol cano. High waves on 22 March pre vented a science team from In for ma tion Con tacts: Laurent Michon and Pat rick landing on the is land, where CVGHM had hoped to in stall Bachélery, Laboratoire GéoSciences Réunion, Institut de instru ments that could be moni tored from the obser va tion Physique du Globe de Paris, Université de La Réun ion, post at Lewotolo volcano, ~ 52 km SSW. Obser va tions on CNRS, UMR 7154-Géologie des Systèmes Volcaniques, 22 March described ash plumes from the sum mit crater ris- La Réun ion, France; Thomas Staudacher and Valérie ing as high as 2 km and ashfall killing trees within a 500-m Ferrazzini, Observatoire Volcanologique du Piton de la radius of the summit on the southern and eastern slopes. Fournaise, Institut de Phy sique du Globe de Paris, 14 route White emis sions with in ter mittent dense gray plumes also nationale 3, 27 ème km, 97418 La Plaine des Cafres, La origi nated from a loca tion on the E foot of the mountain, Réunion, France (URL: http://ovpf.univ-reunion.fr/); Joan with the clouds rising up to 250 m. A small cone grew there Marti, In stitute of Earth Sci ences “Jaume Almera,” Consejo with a crater diam eter of ~ 10 m. From a vantage point on Su pe rior de Investigaciones Cientificas, Bar celona, Spain. Lembata, other observ ers reported minor ashfall, smelled sulfur odors, heard explo sion noises, and saw incan des cent blocks ejected to heights of ~ 500 m that landed in the sea. Me te o ro log i cal clouds con tin ued to in ter mit tently ob- scure sat ellite obser va tions during 23-30 March, but avail- Batu Tara able clear imag ery and CVGHM re ports in di cated con tin u - ing plumes at low alti tudes extend ing as far as 90 km Lesser Sunda Islands, Indo ne sia downwind (figures 4 and 5). Infra red anoma lies also con- 7.792°S, 123.579°E; sum mit elev. 748 m tinued to be recorded during this time. On the morning of All times are local (= UTC + 8 hours) 31 March a plume was seen extend ing about 150 km NNW. CVGHM reported ob serva tions from 30 March that in - On 1 July 2006 a pilot reported an ash cloud from Batu dicated the E side of the volcano had been most impacted Tara drifting NW at 1.5 km alti tude, but the Darwin VAAC by re cent ac tiv ity. Plant life on the E side was af fected by could not iden tify ash in MTSAT sat el lite imag ery around hot ashfall. White plumes rose from the summit to an al ti- the same time. No other evi dence or reports could confirm a tude of ~ 1.7 km and drifted E. Incan des cent rockslides and re newal of ac tiv ity at this small un in habited is land volcano, cooled lava flows were observed at the E foot of the vol- which last erupted during 1847-1852. Starting in Janu ary cano. Steam and occa sional ash plumes rose from the area 2007, there were sat el lite ther mal anom a lies sug gest ing an where hot mate rial in ter acted with the sea. eruption. Two months later observ ers issued reports of ash Semi-contin u ous eruptions through 3 April produced plumes from ex plo sive ac tiv ity. low-level plumes, gener ally to alti tudes of 1.5-3 km, re- MODIS in fra red sat el lite data, com piled and an a lyzed ported by ground observ ers and seen in satel lite im agery to by the Hawai’i Insti tute of Geophys ics and Plane tol ogy distance of 37-56 km downwind in vari ous direc tions. On 5 (HIGP) Thermal Alerts System, first showed anoma lies at April, plumes rose to 3 km alti tude. Based on sat el lite imag - Batu Tara on 17 Janu ary 2007. For almost a year thermal ery the CVGHM reported that on 5 April a lava flow on the sig na tures typ ically were de tected ev ery 1-3 days, some- E slope created a cen tral levee with de bris fans on ei ther times every 4-5 days, with rare gaps of 6-7 days. After no side. The delta-like shape spanned about 450 m across. A anom a lies dur ing 9-17 Jan u ary 2008, reg u lar hotspots re- lava flow also extended 100 m into the water. Diffuse turned and were contin u ing at the end of the month. plumes seen in sat el lite imag ery rose to al titudes of 1.5 km The Darwin VAAC reported that an ash cloud seen in and drifted W and NW dur ing 4-11 April. Ex plosive activ - MTSAT and Terra MODIS imag ery at 1633 on 13 March ity pro duc ing no tice able ash plumes gen er ally de clined in 2007 reached an alti tude of 4.3 km and drifted N. By 0833 April, and on the 12th the hazard status was lowered to Volcanism Network, Volume 32, Number 12, December 2007 Anatahan 5

alti tude of 3 km and drifted N and W. Despite time gaps when plumes were not seen and the de creased fre quency of explo sion plumes, MODIS data recorded thermal anoma - lies at least every few days throughout April-Octo ber 2007, and continuing into February 2008. Geo logic Sum mary. The small iso lated island of Batu Tara in the Flores Sea about 50 km N of Lembata (formerly Lomblen) Island con tains a scarp on the eastern side sim ilar to the Sciara del Fuoco of Italy’s Stromboli volcano. Vege - tation covers the flanks of Batu Tara to within 50 m of the 748-m-high sum mit. Batu Tara lies N of the main vol canic arc and is noted for its potassic leucite-bear ing basanitic and tephritic rocks. The first histor i cal eruption from Batu Tara, during 1847-52, produced explo sions and a lava flow. In for ma tion Con tacts: Cen tre of Vol ca nol ogy and Geo log i cal Haz ard Mit i ga tion (CVGHM), Diponegoro 57, Bandung, Jawa Barat 40122, Indo nesia (URL: http://portal. Figure 4. Aerial photo graph of Batu Tara erupt ing in late March 2007 with an ash plume blowing NE. View is towards the SSE from a Garuda Boeing vsi.esdm.go.id/joomla/); Dar win Vol ca nic Ash Ad vi sory 737 flight be tween Timika, Papua New Guinea and Bali, In do nesia. Cen tre (VAAC), Bu reau of Me te o rol ogy, North ern Ter ri- Lembata Island is in the right back ground. Courtesy of Michael tory Regional Office, PO Box 40050, Casua rina, Northern Thirnbeck. Ter ri tory 0811, Aus tra lia (Email: dar [email protected]. au; URL: http://www.bom.gov.au/info/ vaac/); Mi chael Thirnbeck, Ja karta, In do ne sia (http://www.flickr.com/photos/thirnbeck/); Hawai’i Insti tute of Geophys ics and Plane - tology (HIGP) Thermal Alerts System , School of Ocean and Earth Sci ence and Technol ogy (SOEST), Univ. of Hawai’i, 2525 Correa Road, Hono lulu, HI 96822, USA (URL: http:// hotspot.higp.hawaii.edu/).

Anatahan Mariana Is lands, Central Pa cific 16.35°N, 145.67°E; sum mit elev. 790 m All times are local (= UTC +10 hours)

During mid 2007 and into early Febru ary 2008, Figure 5. Aerial photo graph of Batu Tara erupt ing in late March 2007 Anatahan (fig ure 6) dis charged oc ca sional sig nif i cant show ing a steam plume and a smaller ash puff. View is to wards the SE plumes, as rest less seis mic ity as so ci ated with in ter mit tent from a Garuda Boeing 737 flight between Timika, Papua New Guinea and Bali, Indo nesia. The bay on the left opens to the E. Courtesy of Michael eruptions contin ued. Key source data for this report came Thirnbeck. from the U.S. Geolog i cal Survey (USGS), the Emergency Manage ment Office of the Common wealth of the Northern Mariana Is lands (EMO), NASA Earth Ob serva tory, and the Alert Level 2. However, hotspots continued to be recorded Washing ton Volcanic Ash Advisory Center (VAAC). on an almost daily basis. The same day MODIS ac quired this im age, the U.S. Air A pilot reported a low-level ash plume extend ing 90 km Force Weather Agency reported an odor of sul fur on the is- W on 27 April, but ash could not be identi fied in satel lite land of Guam, ~ 200 km SW of Saipan, which also suggests data. Based on sat ellite imag ery and CVGHM, the Dar win the presence of vog. USGS and EMO air quality instru - VAAC issued re ports of diffuse low ash plumes drifting W ments on Saipan recorded a maxi mum 5-minute aver age of during 5 and 10-12 May. On 19 June an ash plume rose to 959 ppb sulfur diox ide (SO2) and 99 ppb hy drogen sul fide an al ti tude of 1.7 km. Clouds inhib ited visual ob serva tions (H2S) on 18 March. Although such plumes can cause clo- on the other days during 18-25 June. However, on 19 June, sure of the Saipan airport and result in health risks to a dense white plume rising to 1,000 m high was observed. Saipan resi dents, such problems were not mentioned in Between 28 June and 1 July, diffuse white plume was ob- reports of this incident. served rising to 50-150 m. An ash column reached 750 m Crater lake disap pears. Seis mic ity re mained rest less above the summit. and in ter mit tent plumes con tin ued to dis charge from Based on ob ser va tions of sat el lite im ag ery, the Dar win Anatahan during late 2007 and into 2008. By 31 Janu ary VAAC reported that on 18 Septem ber, diffuse ash plumes 2008 the crater lake had disappeared. rose to an alti tude of 2.4 km and drifted W for 140 km. Dis tinct increases in ampli tude of seis mic tremors oc- CVGHM lowered the Alert Level to 1 on 9 Octo ber. During curred on 26 and 28 Novem ber 2007. Explo sions were also 3 Septem ber-9 Octo ber, plumes rose to an alti tude of ap- observed, with rates peaking on 28 Novem ber at several per proxi mately 1.4 km, 700 m above the summit. Satel lite im - minute. This in crease prompted rais ing the alert level to agery showed an ash plume on 13 Octo ber that rose to an Yel low/Ad vi sory on 29 November. 6 Anatahan Smithsonian Institution — Bulletin of the Global

summit caldera. The larger west ern por tion of the cal dera is 2.3 x 3 km wide, and its western rim forms the island’s 790-m high point. Ponded lava flows overlain by pyroclastic de pos its fill the floor of the west ern cal dera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern portion of the caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. A subma rine volcano, NE Anatahan, rises to within 460 m of the sea surface on the NE flank of the volcano, and numer ous other subma - rine vents are found on the NE-to-SE flanks. Sparse ness of vege ta tion on the most recent lava flows on Anatahan had indi cated that they were of Holo cene age, but the first his- tori cal eruption of Anatahan did not occur until May 2003, when a large ex plosive eruption took place forming a new Fig ure 6. Sat el lite image of Anatahan in early 2008. Bright white areas are crater inside the eastern caldera. clouds. A diffuse plume dirfting NW appears to be origi nat ing from In for ma tion Con tacts: Emer gency Man age ment Of fice fumaroles in the east ern crater. Cour tesy of Google Earth and Dig i tal of the Common wealth of the Northern Mariana Islands Globe, accessed 20 Febru ary 2008. (EMO-CNMI) and USGS Ha waii Vol cano Ob ser va tory, PO Box 100007, Saipan, MP 96950, USA (URL: http://www. On 14 Decem ber 2007 the Washing ton Volca nic Ash cnmiemo.gov.mp/ and http://volcano.wr.usgs.gov/ Advi sory Center (VAAC) reported a steam plume visi ble in cnmistatus.php); U.S. Air Force Weather Agency (AFWA)/ satel lite data, but no in di cation of ash. There was a small XOGM, Offutt Air Force Base, NE 68113, USA (Email: surge in seismic activ ity recorded on 16 Decem ber that de - [email protected]); NASA Earth Ob ser va tory creased to previ ous levels by the following day. Accord ing (URL: http://earthobservatory.nasa.gov/); Wash ing ton Vol- to the U.S. Air Force Weather Agency, a plume on 30 De- ca nic Ash Ad vi sory Cen ter (VAAC), Sat el lite Anal y sis cember con sisted pri marily of steam and gas, with lit tle ash Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science content. Seismic tremor levels increased 16 Janu ary 2008 Center Room 401, 5200 Auth Rd., Camp Springs, MD and persisted. 20746, USA (URL: http://www.ssd.noaa.gov/); Google On 31 Janu ary 2008, satel lite data showed that the lake Earth (URL: http://earth.google.com/). in the E crater, a water body whose level had been dropping since Septem ber 2007, had disap peared. Accord ing to the USGS, the tremor indi cated that the volcano may have entered a new phase within its current epi sode of unrest, and the dis ap pear ance of the lake suggested that the mag matic heat source may have moved closer to the surface. Ash emissions occurred at Anatahan on 3 Febru ary 2008. Satel lite images showed a diffuse ash plume extend - ing W for ~ 100 km. It was not possi ble to deter mine pre- cisely the al titude of this ash plume from the currently available data, but it was likely less than 1,500 m. On 5 Feb ru ary, the USGS re ported per sis tent el e vated seis mic tremor and contin ued detec tion of SO2 in sat el lite data. The USGS changed the Avia tion Color Code to Orange and the Alert Level to Watch as a re sult of the ash emissions. A satel lite image (figure 7) shows the volca nic island on 6 Febru ary 2008. Dwarfed by clouds overhead, the island re leased a faint plume (pre sumably bear ing lit tle if any ash) blowing WNW. Data from the satel lite-based Ozone Moni - toring Instru ment (OMI) showed a low-level SO2 plume ex- tending W to SW from the volcano. No thermal anoma lies have been measured by MODIS satel lites over Anataham since June 2006. In a recent publi - cation, Hilton and oth ers (2007) re ported on newly derived SO2 emission rates for Anatahan. Ref er ence: Hilton, D. R., Fischer, T. P., McGonigle, A. J. S., and de Moor, J. M., 2007, Variable SO2 emission rates for Anatahan vol cano, the Com monwealth of the Northern Mariana Is lands: Im pli ca tions for de riv ing arc-wide vol a tile Fig ure 7. Anatahan released plumes of ash and steam in early Febru ary fluxes from erupt ing vol ca noes: Geo phys i cal Re search Let - 2008, con tin u ing a pat tern of in ter mit tent ac tiv ity from the pre vi ous ters, v. 34, p. L14315, doi:10.1029/2007GL030405. De cem ber. The Mod er ate Res o lu tion Im ag ing Spectroradiometer (MODIS) on NASA’s Aqua sat el lite cap tured this image on 6 Feb ru ary Geo logic Sum mary. The elongate, 9-km-long island of 2008. In this im age, a dif fuse pale gray plume blows W from the volca nic Anatahan in the cen tral Mariana Is lands con sists of a large is land and over the Pa cific Ocean. NASA im age cour tesy the MODIS stratovolcano with a 2.3 x 5 km, E-W-trending compound Rapid Re sponse Team at NASA GSFC. Volcanism Network, Volume 32, Number 12, December 2007 El Chichón 7

the June-Oc to ber rainy sea son. The sa lin ity was greater Bezymianny when the lake had higher vol ume. This obser va tion im plies that the direct input of rainwa ter is not a major contrib u tor Kamchatka Pen in sula, Rus sia to lake volume. Instead, rainwa ter is thought to infil trate 55.978°N, 160.587°E; summit elev. 2,882 m into the crater floor and then discharge into the lake through the boiling springs. In BGVN 32:11, we erro ne ously reported a cloud height These springs alter nate between peri ods of high- and of 35 km from Bezymianny on 10 Novem ber 2007. The low-water discharge feeding the lake. The peri ods of high plume on that day was a steam plume that extended ~35 km discharge at the springs corre spond to peri ods when the down wind. lake grows. The peri ods of low discharge at the springs cor- Ref er ence: Cergey Ushakov, Kamchatkan and North- respond to vapor discharge there, inter vals when the lake ern Kuriles Vol ca nic Ac tiv ity, KVERT IN FOR MA TION shrinks. RELEASE 57-07, Satur day, Novem ber 10, 2007, 03:30 In gen eral, on go ing mea sure ments sug gest de creas ing UTC (15:30 KDT). concen tra tions for the boil ing spring and crater lake waters with time. This suggest an absence of new magmatic input

El Chichón México 17.360°N, 93.228°W; sum mit elev. 1,050 m All times are local (= UTC - 6 hours)

On 4 Novem ber 2007, at midnight, a landslide along the Grijalva river bur ied a set tlement (Juan de Grijalva, Municipio de Ostuacán, Chiapas) located ~ 25 km WSW from the 1982 crater. The event, the subject of a report in the news pa per La Jornada, was reported to have buried 40-60 dwellings and killed at least 10, but more likely 200-300 residents. Concern arose as to whether the event was triggered by El Chichón volcano. The scien tists authoring this report, which included those from the Instituto de Geofísica of the Fig ure 8. The crater lake at El Chichón when it contained the smallest Universidad Nacional Autónoma de México (UNAM), water vol ume ever re corded here (5 June 2005). The crater diam e ter is ~ 1 noted that low-frequency rumbling (presum ably tremor) km. Cour tesy of L. Rosales. can clearly be felt in side the ac tive crater. They asso ciated these per tur ba tions with the hy dro ther mal system. The authors consid ered the pertur ba tions too small to cause the distant landslide. Accord ing to the au thors, the landslide at the Grijalva river was proba bly the result of mor pho log i cal in sta bil ity af ter heavy rain fall, rather than as so ci ated with El Chichón behavior. However, in the after math of the 1982 eruption, El Chichón’s nearby flanks still contain abundant unsta ble Fig ure 9. The crater lake at El Chichón when it con tained the larg est wa ter slopes, and the new vege ta tion fails to keep up with the ero- volume ever recorded here (26 March 2007). Cour tesy M. Jutzeler. sion rate. Also, intracrater ava lanches still oc cur, par ticu - larly after heavy rainfall. Accord ing to co-author Dmitri Rouwet, the rumbling beneath the crater often triggers small intracrater avalanches. El Chichón was the scene of large Plinian eruptions in 1982, and the crater hosts a shallow crater lake that has drasti cally varied in size since Janu ary 2001. Figure 8 shows the lake in 2005, the smallest volume at this crater lake yet observed. In March 2007 (figure 9) the lake contained the largest volume yet observed (~ 6 x 105 m3). Boil ing springs. The changes in lake volume stem largely from variable discharges at a boiling spring, rather than merely re flect ing di rect input from rain fall and evap o ra tion. During 2001, 2004 and 2007 a large-volume lake was asso ci ated with a high discharge (over 10 kg/s) into the lake. Saline, near-neutral pH water pours from a boiling geyser-like spring on the lake’s N coast. This took place in Fig ure 10. The crater lake at El Chichón crater lake as seen on 20 months such as Janu ary, only a few months after the end of De cem ber 2007. Courtesy A. Mazot. 8 Fuego Smithsonian Institution — Bulletin of the Global since 1982. After the 2007 rainy season the lake volume de- Coyoacan, CP 04510, Mexico DF, Mexico (URL: http:// creased, coin cid ing with a change to pure vapor emission www.geofisica.unam.mx/vulcanologia/span ish/per sonal. from the geyser-like spring since August 2007 (figure 10). html); Nick Var ley, Cen tre of Exchange and Re search in Tremor, gas fluxes, infer ences, and ongo ing moni tor - Vol ca nol ogy, Faculty of Sci ence, Uni ver sity of Colima, ing. The authors of this report inferred that the low-fre- Av. 25 de Julio #965, Col. Villas San Sebastián, C.P. 28045 quency tremor and rumbling beneath the crater floor Colima, Colima, México (URL: http://www.ucol.mx/ciiv/ stemmed from fluid migra tions inside the boiling aquifer, nick/per sonal_en.htm); Mar tin Jutzeler, Centre for Ore De- sometimes causing small intra-aquifer phreatic explo sions. posit Research (CODES), Univer sity of Tasma nia, Austra - Nev er the less, crater floor in spec tion dur ing De cem ber lia; and Laura Rosales Lagarde, Earth and En vi ron men tal 2007 found it unbro ken (without evi dence of rupture or Sci ence De part ment, New Mex ico Tech, Socorro, NM, breach ing). The crater mor phol ogy, no ta bly the dis tri bu tion USA; La Jornada (URL: www.jornada.unam.mx/). of fumarolic fields, has on the whole remained sta ble since shortly after the 1982 eruptions. The CO2 gas fluxes from the crater lake’s sur face and floor were re cently sam pled us ing a float ing ac cu mu la tion Fuego chamber to measure the out put. The calcu lated mean emission rate at the lake’s surface in March 2007 was 1,500 g / Gua te mala (m2 @ day), and in Decem ber 2007 a prelim i nary esti mate 14.473°N, 90.880°W; sum mit elev. 3,763 m was 860 g / (m2 @ day). A prelim i nary flux rate from the All times are local (= UTC - 6 hours) crater floor in Octo ber 2007 was 1,930 g / (m2 @ day). In ad di tion, in fra red cam era im ages proved use ful to Eruptive ac tiv ity has contin ued at Fuego be tween Janu - quantify the thermal output. A good corre la tion appeared ary 2007 and early Febru ary 2008. Typi cal activ ity during between gas flux and ground temper a ture. This may offer this in ter val con sisted of ex plo sions that gen er ated ash poten tial for future monitoring. plumes up to ~ 2 km above the summit (~ 6 km alti tude) The authors inferred that future El Chichón vol ca nism and caused local ashfall (reported up to ~ 15 km away, but might take the form of intracrater dome growth. Such from one eruption, ~ 25 km away). Strombolian eruptions, growth could fol low changes in chem istry, tem pera ture and ava lanches, and lava flows up to ~ 1.5 km long were also dy namics of the crater lake, the de gas sing re gime, seismic - commonly reported. Pyroclastic flows traveled up to ~ 2 ity, geomag ne tism, crater morphol ogy, or other unrest such km. Blocks detach ing from the front of the flows and as the onset of phreatic ex plosions. Such processes can oc- bounc ing downslope were of ten in can des cent. Sat el lite im - cur very rapidly, as recently shown by the dome growth at agery often detected hotspots. Shock waves and rumbling Kelud, Indo ne sia, in Novem ber 2007. However, the au- or loud noises, sometimes described as simi lar to a passing thors’ inves ti ga tion found no evidence to support current air plane, were com monly no ticed. Out last re port discussed dome growth. events through Decem ber 2006 (BGVN 32:11). Future updates on the activ ity of El Chichón can be Details in cluded in the text below were provided by the found on the CVL-IAVCEI website (http://www.ulb.ac.be/ Instituto Nacional de Sismologia, Vulcanología, sci ences/cvl/in dex.html). Meteorología e Hidrologia (INSIVUMEH), the Geo logic Sum mary. El Chichón is a small, but power ful Coordinadora Nacional para la Reducción de Desastres trachyandesitic tuff cone and lava dome complex that occu - (CONRED), and the Washing ton Volca nic Ash Advi sory pies an isolated part of the Chiapas region in SE México far Cen ter (VAAC). from other Holo cene volca noes. Prior to 1982, this rela - The photo graphs in cluded in this re port are by Richard tively unknown volcano was heavily forested and of no Roscoe, who on his website (www.photovolcanica.com) greater height than adja cent non-volca nic peaks. The larg- features more Fuego photos than we can include here. He est dome, the former summit of the volcano, was con- also includes a brief ani ma tion of a small Fuego eruption. structed within a 1.6 x 2 km summit crater created about His site also provides a begin ner’s guide to vol cano photog - 220,000 years ago. Two other large domes are located on raphy as well as cautions about safety and trekking in the the SW and NW flanks. A horse-shoe shaped explo sion area. All of his photos are used with his permis sion. They crater on the SE flank of El Chichón wit nesses past explo - were taken during 29-31 De cem ber 2007. A com panion site sive ac tiv ity, now host ing the Agua Caliente thermal by his col leagues M. Rietze and Th. Boeckel also de scribes springs. Eleven large explo sive eruptions have occurred their photo excur sion. Figures 11-13 are broadly repre sen - during the last 8,000 years. The power ful 1982 explo sive tative of the kinds of eruptions com mon at Fuego during the eruptions of high-sulfur, anhydrite-bearing magma de- report ing inter val, and they provide a feel for the regional stroyed the summit lava dome and were accom pa nied by setting and geography. pyroclastic flows and surges that dev as tated an area ex tend - During 4-5 Jan u ary 2007 gas-and-ash clouds rose to 4. ing about 8 km around the volcano. The eruptions cre ated a 2-4.8 km al ti tude and con stant in can des cent av a lanches new 1-km-wide, 300-m-deep crater that now contains an from the cen tral crater and a lateral crater ~ 70 m from the S acidic crater lake. edge of the cen tral crater de scended SW to wards Taniluyá In for ma tion Con tacts: Dmitri Rouwet, Istituto ravine. Fine ashfall was noted in areas S and ~ 9-15 km SW Nazionale di Geofisica e Vulcanologia (INGV-Palermo), of the summit. On 12 Janu ary there was explo sive ejecta Sezione di Palermo, Via Ugo La Malfa 153, CAP 90146, and ash plumes up to 4 km alti tude. Incan des cent mate rial Palermo, It aly (URL: http://www.pa.ingv.it/); Agnes was propelled up to 75 m above the sum mit and incan des - Mazot, Loic Peiffer, and Yuri Taran, Instituto de Geofisica, cent blocks rolled W towards Taniluyá ravine and Santa Universidad Nacional Autonoma de Mexico, Ciudad Teresa ra vine, and S to wards Cenizas ra vine. Ex plo sive ac - Universitaria, Circuito Ex te rior s/n, Col. Copilco, Del. tivity was reported again during 21-29 Janu ary when incan - Volcanism Network, Volume 32, Number 12, December 2007 Fuego 9

Figure 11. A view of Fuego in eruption as seen from the city of Antigua. Note twin church spires along the photo’s lower mar gin. Fuego (erupting at left) is only one of several volca noes in this photo; progres sively farther towards the right peaks consist of Meseta, Acatenango (highest), and Yepocapa. This copy righted photo is from around 29-31 Decem ber 2007. Used with per mis sion of pho tog ra pher Rich ard Ros coe.

des cent mate rial and blocks were ejected 100 m above the summit; blocks rolled ~ 500 m S and SW. On 26 and 29 Janu ary glowing blocks from lava-flow fronts rolled S towards Cenizas ravine. During an overnight visit to a neigh- boring summit, Craig Chesner and Sid Halsor saw Strombolian eruptions at roughly half-hour intervals. No ac tiv ity was re ported af ter late Jan u ary un til 9-13 March 2007, when lava flows were noted extend ing ~ 100-150 m W toward Taniluyá ravine and explo sive ash plumes rose to 4-4.2 km alti tude. On 12 March glowing material was ejected ~ 15-20 m above the central crater. Lava flows on 15 March and explo sive incan des cent ejecta thrown 200 m above crater rim were accom pa nied by an Figure 12. An explo sive plume rising verti cally above Fuego’s summit on 29 Decem ber 2007, with wisps of fall ing ash visi ble on the right side. The ash plume. The longest lava flows traveled ~ 1.5 km W to- photo was taken from Antigua. Copy righted photo by Richard Ros coe. ward Taniluya ra vine. Sim i lar ac tiv ity con tin ued the next day, with previ ous lava flows advanc ing and new flows seen in differ ent ravines. Pyroclastic flows also oc curred, ash plumes rose to 4-6 km alti - tude. Shockwaves were felt ~ 15 km away, and Strombolian eruptions propelled glowing tephra 300 m above the summit. Two pyroclastic flows traveled about 800 m; one NW, and another W and SW. During most days 21-27 March Fuego emitted explo sive gas-and-ash plumes that rose to ~ 4.7-5.1 km alti tude, causing ashfall in ar eas 5-8 km SSE and 9 km W. On 24 March explo sions were followed by lava blocks roll- ing down the W flank toward Taniluyá ra vine. Sim i lar ac tiv ity on 26 March caused ashfall in areas 10-25 km to the W and SE. The next reports of activ ity, during 20-23 April, were of lava flows, pyroclastic flows, explo - Figure 13. Incan des cent ejecta from Strombolian eruptions of Fuego taken from the N on Acatenango volcano sive in can des cent ejecta 50-75 m (~ 4 km ele va tion). The exact date was surmised from text as 30 Decem ber 2007. The shape of Fuego’s sum mit above the vent, and a gas-and-ash has been modi fied by the growth of a sharp peak, presum ably due to the accu mu la tion of spatter and cinder. The plume up to 4 km alti tude. Incan - night-time expo sure also captured in the background the lights of towns on the Pacific coastal plain to the S. des cent ma te rial de scended 300 m Copyrighted photo by Richard Ros coe. 10 Fuego Smithsonian Institution — Bulletin of the Global down the S and W flanks. The Washing ton VAAC reported alti tude. Ava lanches from cone building in the inner crater that an intense hotspot seen on satel lite im agery on 21 April went W into the Taniluyá and Santa Teresa ravines. was likely caused by a lava flow to the SW. On 23 April a On 12 Octo ber, INSIVUMEH reported that explo sions pyroclastic flow and in can des cent av a lanches trav eled from Fuego produced ash plumes that rose to alti tudes of 4. down SE and SW ra vines; ash explo sions caused light 2-4.8 km and caused ashfall in areas to the W. The explo - ashfall in areas S. sions were accom pa nied by rumbling, and degas sing Obser va tions during 17-19 May were of fumarolic sounds; shock waves were detected up to15 km away. The emissions ~ 600 m high along with active lava flows ex- Washing ton VAAC reported a thermal anomaly on satel lite tending ~ 100 m SW toward the Taniluyá ravine and ~ 500 imag ery along with ash plumes that drifted W and NW. m SW toward the Cenizas ravine. The lava flow from the Ac cord ing to Wash ing ton VAAC, sat el lite im ag ery de- edge of the central crater contin ued on the S flank (~ 150 m tected multi ple ash “puffs” emitting from the volcano be- long); landslides of blocks of in candes cent mate rial spalled tween 24-30 Octo ber. They also reported ash plumes on 20 from the front of the flow into the Taniluya ravine. Activ ity Novem ber (4.6 km in alti tude) and 29 Novem ber. Addi - the follow ing week, 26-27 May, consisted of explo sive tional weak to moder ate explo sions occurred on 7 Decem - ejecta ~ 100 m above vent, gray steam-and-ash plumes up ber and 12 Decem ber, expel ling ash and causing degas sing to 4-4.6 km alti tude, and block ava lanches to the S and SW. sounds. Shock waves were noticed up to 15 km away. On 28 May the lava flow on the S flank contin ued to ad- On 15 De cem ber, Fuego gen er ated a sig nif i cant vance and produce incan des cent blocks that rolled W in ash-and-steam plume that was observed from Antigua and Taniluya ra vine. Explo sive in can des cent ejecta was seen on Guate mala. It also produced a consid er able flow of ash (and 29 May, along with lava flows that extended ~ 400 m SW possi bly lava) down its E slopes. Accord ing to the Wash- to ward Cenizas ra vine and in can des cent material rising tens ing ton VAAC, sat el lite im ag ery de tected a ther mal anom aly of meters above the vent. on 15-16 De cem ber. There af ter, Fuego’s ac tiv ity de clined On 1-2 August, pyroclastic flows occurred and explo - to normal levels, although a few moder ate explo sions con- sive ejecta was thrown 50-75 m above the crater rim; an ash tinued, along with an occa sional ash plume. An ash cloud plume rose to 5.3 km alti tude. Incan des cent ava lanches from Fuego was observed on 21 December and 26 traveled 500-700 m down the S and W flanks. On 2 August, December 2007. a moder ate eruption produced a pyroclastic flow that trav- For 11 Janu ary and 24 Janu ary 2008, INSIVUMEH re- eled ~ 2 km SSW down the Cenizas ravine. A resul tant ported weak explo sions from Fuego that produced ash plume produced ashfall S, SW, and W for several minutes. plumes that rose to alti tudes of 4-5 km. Small ava lanches of On 8-9 August, pyroclastic flows and explo sive blocks traveled W toward the Taniluyá ravine. Based on re- Strombolian activ ity occurred with a gas-and-ash cloud to ports from INSIVUMEH, CONRED reported on 28 Janu - 4.4-5.6 km alti tude. This eruption was visi ble from the city ary that the Alert Level was low ered to Green. On 30 Jan u - of Antigua, even though the result ing lava flows primar ily ary, sat ellite imag ery de tected a nar row plumes of gas and trav eled down the S and W flanks, which were on the side pos si ble ash. On 4 Feb ru ary, sat el lite im ag ery de tected ash op po site from Antigua. Clouds obscured the view of possi - plumes that rose to an altitude of 5 km. ble E-flank lava flows. Ashfall was reported in ar eas to the Geo logic Sum mary. Volcán Fuego, one of Central W. Lava flows and related detached blocks traveled 1.5 km America’s most active vol canoes, is one of three large down Cenizas ra vine to the SW. Sev eral pyroclastic flows stratovolcanoes over look ing Gua te mala’s for mer cap i tal, descended the flanks. Ashfall was reported in villages to the Antigua. The scarp of an older ed ifice, Meseta, lies be tween W, SW, and S. 3,763-m-high Fuego and its twin volcano to the N, On 10-13 August, small explo sions and ash plumes rose Acatenango. Con struc tion of Meseta volcano dates back to up to 4.3 km alti tude. 11 August behav ior was charac ter - about 230,000 years and contin ued until the late Pleisto cene ized by weak explo sions that expelled gray ash to 500 m or early Ho lo cene. Col lapse of Meseta vol cano may have above the crater. On 27 August, lahars carried tree trunks, pro duced the mas sive Escuintla de bris-av a lanche de posit, branches, and blocks down the Lajas drainage to the SE. On which extends about 50 km onto the Pacific coastal plain. 28 August, explo sive ash plumes rose to 4.1 km alti tude. Growth of the modern Fuego volcano followed, contin u ing On 31 August, a lahar 8 m wide and 1.5 m thick descended the Sward migra tion of volca nism that began at W down the Santa Teresa ravine. Acatenango. In contrast to the mostly andesitic Acatenango On 3-4 Septem ber, explo sive ash plumes rose to 4.5 km volcano, eruptions at Fuego have become more mafic with alti tude. On 3 Septem ber, fumarolic plumes rose to 4 km al- time, and most his tori cal ac tiv ity has produced ba saltic ti tude and a 300 m lava flow traveled W down the Taniluya rocks. Fre quent vig or ous his tor i cal erup tions have been re- drain age. There were also av alanches in the Cenizas ra vine. corded at Fuego since the on set of the Spanish era in 1524, On 21 Septem ber explo sions of gray ash rose to ~ 5.8 km and have produced major ashfalls, along with occasional alti tude and incan des cent pulses in the crater rose to 75 m pyroclastic flows and lava flows. with ava lanches in the S and SW flank. On 24 Septem ber In for ma tion Con tacts: Instituto Nacional de 2007, mod er ate and strong ex plo sions oc curred, ac com pa- Sismologia, Vulcanología, Meteorología e Hidrologia nied by ash plumes ex tending up to 900 m above the crater, (INSIVUMEH), Ministero de Communicaciones, and constant degas sing sounds for peri ods of up to 20 min. Transporto, Obras Públicas y Vivienda, 7a. Av. 14-57, zona On 5 Oc to ber, weak to mod er ate in can des cent ex plo sions 13, Gua te mala City 01013, Gua te mala (URL: http://www. occurred, accom pa nied by ash plumes up to 800 m above insivumeh.pagina.de); Coordinadora Nacional para la the crater, and degas sing sounds. Block avalanches were Reducción de Desastres (CONRED), Av. Hincapié 21-72, noted in the Taniluyá and Santa Teresa ra vines. Zona 13, Guate mala City, Gua temala; Wash ing ton Vol ca- On 10 Octo ber, weak to moder ate explo sions occurred, nic Ash Advi sory Center (VAAC), Sat el lite Anal y sis Branch the largest accom panied by ash plumes that rose to 4-5 km (NOAA/NESDIS), 4700 Silver Hill Road, Stop 9910, Volcanism Network, Volume 32, Number 12, December 2007 Poás 11

Washing ton, DC 20233-9910, USA (URL: http://www.ssd. crev ices on top of that ter race were also rap idly wid en ing as noaa.gov/); Rich ard Ros coe, PhotoVolcanica.com (URL: joint blocks detach. http://www.photovolcanica.com/); M. Rietze, R. Ros coe, Geo logic Sum mary. The broad, well-vege tated ed ifice and Th. Boeckel, (website) Vol canoes of Cen tral America, of Poás, one of the most active volca noes of Costa Rica, Volcan Fuego, Guate mala 29th-31st of Dec. 2007 (URL: con tains three craters along a N-S line. The fre quently vis- http://www.tboeckel.de/EFSF/efsf_wv/fuego_07/ ited multi-hued summit crater lakes of the ba- fuego_07_e.htm); Craig Chesner, East ern Il li nois Uni ver- saltic-to-dacitic vol cano, which is one of Costa Rica’s most sity, Charleston, Il linois, USA; Sid Halsor, Wilkes Barre prom i nent nat u ral land marks, are eas ily ac ces si ble by ve hi - University, Wilkes Barre, PA 18766, USA. cle from the nearby cap ital city of San José. A N-S-trending fissure cutting the 2,708-m-high com plex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The Poás southern most of the two summit crater lakes, Botos, is cold and clear and last erupted about 7,500 years ago. The more Costa Rica 10.20°N, 84.233°W; sum mit elev. 2,708 m All times are local (= UTC - 6 hours)

A small phreatic eruption took place from the crater lake at Poás (figure 14) on 13 Janu ary 2008. Vari ous changes such as the loss of fumaroles and minor mass wast - ing have also occurred at the intracrater dome. The 13 Janu - ary erup tion was de scribed in a re port by Eliecer Duarte of the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA). Our previous re port dis cussed Sep tem ber 2006-Sep tem ber 2007 and noted hydro ther mal varia tions and a minor phreatic erup tion (BGVN 32:09). A small phreatic eruption occurred at 0900 on 13 Jan u- ary from the hot, acidic Laguna Caliente. Carlos Cordero, a park ranger who witnessed the event, indi cated that the event ejected wa ter and sed iments from the lake’s center to a height of ~ 200 m. This mate rial mainly fell back into the lake, changing its color from a dark green to an intense white (figure 15). The event was also seen by a group of tourists who watched from the main viewpoint ~ 1 km S of the lake. The eye-wit ness re port em pha sized the calm con - ditions of the lake and dome before the eruption. Post-eruption inspec tion of the crater by OVSICORI staff revealed that the explo sion left a 1.5-m-wide band of Figure 14. Topo graphic map of Poás and en vi rons em pha siz ing the crater sedi ment up to 10 cm thick along the entire rim of the lake lake, scene of a 13 Janu ary phreatic eruption. Note the dome and the area (figure 16). Some sedi ment also extended about 8 m from la beled ‘ter race’ on its mar gin. Map by E. Duarte, OVSICORI-UNA. the shore at the S rim, near the ter race of the dome. The de - posits, clearly debris from the lake bottom, included many shin ing crys tals; larger clasts were ab sent. Af ter the ex pul - sion, water flowing back into the lake seem ingly scoured or removed some sediment. Dur ing a visit of OVSICORI staff, the lake’s color changed over about a 3-hour period as a result of gas expul - sion. The rapid degas sing of thick columns of toxic gases obscured visi bil ity of the other side of the lake. Compared to measure ments at the end of Novem ber 2007, the lake’s tem pera ture had dropped (to 45ºC) and the water level had risen 1.5 m. The OVSICORI's staff also found a small landslide (8 x 20 m) on the dome’s N face (figure 17). They described the landslide as a chaotic deposit of heavily altered angu lar blocks in a gray matrix that had been altered by hydro ther - mal activ ity. A slurry of yel lowish ma te ri als reached the edge of the lake. Based on field ev idence, the team con- Figure 15. A picture of the ac tive crater of Poás taken a short time after the cluded that the small land slide took place imme di ately af ter phreatic eruption had ended and the main col umn had collapsed on 13 the emission of sediments. Janu ary 2008. The dome is in front of the steam-covered lake. The shot Figure 18 shows a photo of the dome’s steep E cliff was captured by park ranger Carlos Cordero who stood at the main face. Fumaroles had re cently ceased emerging. Cracks and view point S of the lake. Courtesy of OVSICORI-UNA. 12 Guagua Pichincha Smithsonian Institution — Bulletin of the Global promi nent geothermally heated northern lake, Laguna tori cal eruption was reported in 1828. Poás eruptions often Caliente, is one of the world’s most acidic nat u ral lakes, include geyser-like ejections of crater-lake water. with a pH of near zero. It has been the site of frequent In for ma tion Con tacts: E. Duarte and E. Fernández, phreatic and phreatomagmatic eruptions since the first his- Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori. una.ac.cr/).

Guagua Pichincha Ecua dor 0.171°S, 78.598°W; sum mit elev. 4,784 m All times are local (= UTC - 5 hours)

Fol low ing De cem ber 2007 seis mic ity, Guagua Pichincha gener ated phreatic eruptions multi ple times on 1 Febru ary 2008. The summit lies only ~ 8 km W of the limits Figure 16. A remnant of the dried and solid i fied sedi ments expelled during the 13 Janu ary eruption at Poás. The sedi ments, fine grained and of Ecua dor’s capi tal, Quito. Our last report summa rized light in color, appeared to have come directly from the bottom of the crater events through Janu ary 2004 (BGVN 29:06). lake. Note pocket knife for scale. Cour tesy of OVSICORI-UNA. In lead-up to the phreatic eruptions, the Instituto Geofísico Escuela Politécnica Nacional (IG-EPN), reported that an M 4.1 earthquake occurred in the vicin ity on 6 De - cember 2007, fol lowed a week later by an increase in frac - ture earthquakes. These events, contin u ing through 23 De- cember, were below M 3 and occurred at shallow depths within the volcano. On 24-30 Decem ber 2007, IG-EPN indi cated that the fumaroles were stable. IG-EPN re ported that a slight in crease in activ ity had been observed over a few weeks at the end of Janu ary 2008. This activ ity cul minated on 1 Febru ary with seven phreatic explo sions of moderate size. IG-EPN went on to say that these phreatic eruptions gener ally occur during rainy peri - ods, so these ex plo sions are not nec es sar ily in dic a tive of any in crease in ac tiv ity. Since this type of event may oc cur again, however, IG-EPN recom mended that visi tors not descend into the caldera. This was mentioned in a 2 Febru ary Figure17. This 18 Janu ary photo of the crater lake, shoreline, and adja cent news re port in El Pais, which further mentioned that strong dome at Poás, in di cates the lo ca tion of sev eral small areas where 13 rains that had recently fallen in Quito and the crater. Janu ary depos its still remained. In addi tion, a small por tion of the dome As of 14 Febru ary, Ash Advi so ries cata loged by the had detached and moved downslope in a minor landslide that reached the Washing ton VAAC’s lacked reports describ ing the 1 Feb- lake. Cour tesy of OVSICORI-UNA. ruary, or any subse quent, phreatic eruptions. Geo logic Sum mary. Guagua Pichincha and the older Pleisto cene Rucu Pichincha stratovolcanoes form a broad volca nic mas sif that rises imme di ately to the W of Ec ua- dor’s cap ital city, Quito. A lava dome is located at the head of a 6-km-wide breached caldera that formed during a late-Pleisto cene slope failure of Guagua Pichincha about 50,000 years ago. Subse quent late-Pleisto cene and Holo - cene erup tions from the central vent in the breached cal dera consisted of ex plosive ac tiv ity with pyroclastic flows ac- compa nied by peri odic growth and destruc tion of the central lava dome. Many minor eruptions have occurred since the begin ning of the Spanish era at Guagua Pichincha, which is one of Ecua dor’s most active volca noes. The largest histor i cal eruption took place in 1660, when ash fell over a 1,000 km radius, accu mu lat ing to 30 cm depth in Quito. Pyroclastic flows and surges also occurred, primar - ily to the W, and affected agricultural activity, causing great Figure 18. A photo of the E wall of the dome at Poás, a zone of ac tive slope failure. In this area previ ously active springs and fumaroles had recently economic losses. disap peared leaving only native sulfur depos its at the mouth of former In for ma tion Con tacts: Instituto Geofísico Escuela fumaroles. At the foot of the cliff lies a terrace of de bris from mass Politécnica Nacional (IG-EPN), Apartado 17-01-2759, wast ing. Cour tesy of OVSICORI-UNA. Quito, Ecua dor (URL: http://www.epn.edu.ec/~igeo/).