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 i cally vent ing 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; sum mit elev. 2,632 m Dolomieu’s floor, ac cu mu lat ing dur ing an Au gust All times are lo cal (= 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 tical 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 be gan this volcano since 1760, and one of the few large col lapse erupt ing 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 ex amples of collapses in cluding next day. those in 1968 at Fernandina (Simkin and Howard, 1970) The 30-31 March erup tion included lava foun tains 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 vol canism 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 Dur ing the next few days, seis micity rates rose to by in a recent paper by Michon and oth ers (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 sit u 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 com po 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) reg is- 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 dis- place 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 seis- mic and tremor epi sodes. Each of those consisted of a sharp, post col lapse tremor in crease, fol- lowed 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 oc- curred a parox ysmal phase during Figure 1. Maps taken from Michon and others (2007) showing loca tion and key geog raphy of Pi ton de la which 200 m high lava fountains Fournaise volcano on Re union island. The in set shows the vol cano at the is land’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 fea tures, 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 Vol cano, 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 Pi ton 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 struc tures 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 af ter 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, form ing arc-shaped pla teaus there. On 10 April the caldera had enlarged to en gulf most of the Dolomieu struc ture.