Cooperation on Congo Volcanic and Environmental Risks

Transcription

1 Eos, Vol. 88, No. 6, 7 April 7 VOLUME 88 NUMBER 6 7 APRIL 7 EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL UNION PAGES Cooperation on Congo Volcanic and Environmental Risks PAGES 77,8 On 7 January, the Nyiragongo volcano (.5 S, 9.5 E, 369 meters above sea level), located about 8 kilometers north of Lake Kivu in the Democratic Republic of Congo, erupted, releasing a volume of -3 million cubic meters of lava. Lava flows originated from north-south oriented fractures that rapidly developed along the southern flank of the volcano. Two lava flows divided the nearby city of Goma (-5, people) into two parts, forcing a rapid exodus of the population into Rwanda. One of these lava flows ran into Lake Kivu, encroaching 6 meters below lake level with a submerged lava volume of million cubic meters. About 5% of the town was directly affected, leaving approximately, people homeless. At least 7 people died as a direct consequence of the eruption. Following a United Nations fund-raising event, the U.N. began a -year scientific project with the Goma Volcanological Observatory (GVO) by forming the International Scientific Coordination Committee (ISCC). The goals and objectives of the ISCC were to build up the capabilities of GVO by setting up () a monitoring network with international standards; () a fluid geochemistry laboratory; and (3) an Internet-based system of communication with the international scientific community. The U.N. Office for the Coordination of Humanitarian Affairs sought the involvement of researchers from several Italian scientific institutions. D. Tedesco (a coauthor on this article), who had been involved in a U.N.-sponsored response to a 995 Nyiragongo volcanic crisis, formed a team of researchers R Papale, O. Vaselli, and J. Durieux to work during the January eruptive event. This article describes various proposals later organized by the Italian scientists who were instrumental in helping with the volcano monitoring effort. From May to April, a series of foreign volcanologists and other scientists each spent -month periods at GVO implementing their own projects and upgrading GVO. Among these activities was the establishment of a simple connection to the Internet, which integrated GVO into the volcanological community. Further, training abroad of GVO scientists allowed them to acquire the experience and skills necessary to use modern techniques for volcano monitoring and surveillance. GVO was then able to start a new phase of monitoring and surveillance of the two active volcanoes, Nyiragongo and Nyamulagira, and to disseminate monthly reports. For the first time, GVO was able to participate actively in the international volcanological community. GVO researchers as well as foreign volcanologists who have worked in Goma since have recognized the need to establish a new and updated seismic network to replace the previous analogue seismic network that was looted during Congo's civil war. The GVO staff along with the ISCC developed the technical characteristics of the new seismic network, which was provided by the Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV) and consists of seven broadband telemetered digital stations. In addition, the Italian Civil Defence of the Ministry of Interior, via INGV and in collaboration with GVO personnel, supported a project that investigated likely paths of future lava flows toward Goma. U.N. funds were also used to establish a geochemical laboratory at GVO to provide complete geochemical assistance for the study and monitoring of inland (including the Nyiragongo crater) and sublacustrine gas and water discharges. both the hardware and software had originally been designed for the INGV Seismic Network. The digitizing unit, named Geophysical All Inclusive Acquisition (GAIA) system, is a very low noise, modular system with a portable configuration. The network is composed of enlargedband or three-broadband component sensors that have a -bit analog to digital converting unit, GPS synchronization at the remote station, a radio modem link on the -7 megahertz frequency band, solar panels, and batteries. Lennartz (LE3D-5s seismometer) and Nanometrics Trillium broadband seismometers, each with a Satellite 3A5 radio modem by Satel, were used. Seismic stations are compact, have low power demands, and can transmit a 9. kilobits per second flow using 5 kilohertz of bandwidth. The digital link allows maintenance of the complete -bit dynamic range of the converter. Each remote station is equipped with two or three Helios Technology solar panels, one charge controller, and one battery. GVO scientists and technicians were trained by INGV researchers in Goma and in Rome to maintain the whole system and interpret the seismic data. Owing to difficult security conditions caused by ongoing conflict within the Democratic Republic of Congo, scientists could only install the instruments in seven 'safe havens' that had been established by GVO. To obtain a suitable seismic network geometry around the volcano, three sites (Katale-KTL, Kibumba-KBB, and Kibati-KBT, in Figure la) were located on the eastern side of Nyiragongo, using the third site as relay for the other two stations. The adopted geometry is reliable for efficient monitoring of Nyiragongo volcano and allows seismic activity of Nyiragongo and Nyamulagira volcanoes to be distinguished. Figure la shows the location of the seven telemetered digital stations, with the Nyiragongo and Nyamulagira realms identified. Examples of the new records made available by the network records are shown in Figures la, lb, and lc. BY D.TEDESCO, L. BADIALI, E. BOSCHI, P PAPALE, FTASSI, O. VASELLI, C. KASEREKA, J. DURIEUX, G. DENATALE, A. AMATO, M. CATTANEO, H. CIRABA, G. CHIRICO, A. DELLADIO, M. DEMARTIN, G. FAVALLI, D. F^ANCESCM, V LAUCIANI, G. MAVONGA, G. MONACHESI, N. M. PAGLIUCA, D. SORRENTINO, AND M.YALIRE The Digital Seismic Network The digital telemetered seismic network was especially designed for the Goma volcanic area. The digital acquisition system is a customized version of the INGV seismic acquisition system (namely "frontnet-backnet"), and The Geochemical Network During the eruption, a fracture system developed and generated fumaroles that were monitored by GVO every 5 days by a geochemistry laboratory that was set up at

2 Eos, Vol. 88, No. 6, 7 April 7 ' I ' I GOMA EBZ Z NOV 5 (3), Fig.. (a) Map of Nyiragongo and Nyamulagira volcanoes. Seismic stations, marked as black dots, are located in sites that are both efficient and safe, (b) A local earthquake that occurred on 5 November. (c) A regional earthquake that occurred in Tanzania on November 3 (:3:8.69 ML.3 also in ISC), (d) A teleseism from Sumatra on 5 July (:3:9.9 ML 7. CSEM 69993). Original color image appears at the back of this volume. GVO and equipped with the minimal require ments for a c h e m i c a l laboratory, including spectrophotometers and portable gas analyz ers. GVO scientists were trained in G o m a and in Italy on how to collect and analyze gas and water samples. 'Mazukus' C -rich gas emanations that are c o m m o n l y found at the foot of the v o l c a n o but are deadly for animals as well as humans are also now monitored weekly by the geochemistry labo ratory. Nearly 9 % of the existing mazukus have b e e n identified, mapped, and analyzed by GVO and Italian researchers. GVO pro vides results of its research and r e c o m m e n dations to local authorities, who have modi fied plans for urban development b a s e d on these recommendations. GVO also releases appropriate warnings to inhabitants who live c l o s e to these gas discharges. Another particularly sensitive area is around Lake Kivu ( 6 square kilometers) where G o m a and Gisenyi, Rwanda, are located. This lake is o n e of the deepest (75 meters) in Africa and is the site of a huge C - C H reservoir below 5 meters. Vertical profiles (Figures a and b) have b e e n con structed to a s s e s s the c h e m i c a l stratification of the lake in terms of dissolved gases and isotopic parameters to evaluate the risk asso ciated with a sudden gas release that could affect people living nearby. A release could c o m e from either a sublacustrine eruption or the injection of future lava flows below the critical threshold of 5 meters below the surface. As nearly million people live along the shore of Lake Kivu, such potential events, although unlikely, c a n n o t b e ignored. In May, volcanic activity resumed within the main crater of Nyiragongo, where a new lava lake (presently discharging up to 6, tons per day of sulphur dioxide) had formed. Since S e p t e m b e r, when the vol c a n i c plume r e a c h e d a relatively stable, high emission rate, meteoric waters westward of the main crater (along the main east-west wind direction) have b e e n collected. T h e volcanic plume c a n affect people living along the western flank of the volcano who rely on drinkable meteoric waters. T h e inter action between rainfall and the gas-rich plume often produces acidic waters with ph as low as, and fluoride, chloride, and sul fate contents up to 3,, and milli grams per liter, respectively. (For compari son, the World Health Organization r e c o m m e n d s that drinking water contain no more than.5 milligrams per liter of fluoride to avoid fluorosis.) Crops and vegetation are also affected. GVO currently monitors con centrations of these c h e m i c a l s in meteoric waters. Hazard From Lava Flow Invasion in Goma T h e fissure eruption of Nyiragongo highlights Goma's high risk from lava flow invasion. T h e very fluid and quickly advancing lava that is most c o m m o n l y erupted c a n threaten urban settlements.

3 Eos, Vol. 88, No. 6, 7 April 7 To support GVO's activities, the risk to a r e a s in G o m a m o r e prone to invasion by t h e s e lava flows w a s a s s e s s e d in a long series of numerical simulations, with the s a m e m e t h o d used during Mount Etna eruptions. This m e t h o d is b a s e d on the principle of steepest d e s c e n t path and allows a probabi listic estimate of the a r e a s inundated by lava flows originating from s e l e c t e d s o u r c e s. T h e m e t h o d w a s validated for Nyiragongo lava and topography by repro ducing the paths of the two main lava flows that devastated G o m a in. It w a s then applied to two relevant c a s e s (Figure 3 ) : the arrival of lava flows in town from the north (as in J a n u a r y ), and the further extension of the main eruptive fissure formed in 977. This fissure w a s reactivated and e x t e n d e d in, nearly reaching G o m a. T h e s e simulations have shown that the Kibwe district in G o m a has the least susceptibility to lava flow invasion. In addi tion, further e x t e n s i o n of the eruptive fis sure would result in c o m p l e t e destruction of the international airport (already dam a g e d by lava flows in ), though it would not p r o d u c e much risk to the nearby city of Gisenyi. T h e s e results are being used by GVO personnel w h o have asked l o c a l authorities to incorporate them into plan ning city reconstruction, urban develop ment, and e m e r g e n c y r e s p o n s e to future fis sure eruptions at Nyiragongo. Ib) ?-5 - ' -- - CD > * Kabuno Basin E : ^% CL -35- f- 3 <» -35 Q -- Q -5- Kivu Lake C O. (mmoi) i * i i * i * t 6 i * i * i * i * i C H, (mmoi) Fig.. Chemical and isotopic profiles have been constructed for sites A and B (dots in figure ), located in Lake Kivu. Examples of (a) carbon dioxide (CO^ and (b) methane (CH^ profiles from one of the several chemical, isotopic, and physical studies carried out at Lake Kivu. Squares represent data collected from site A (Kivu Lake) in Figure la and circles from site B (Kabuno basin). Original color image appears at the back of this volume. Conclusions T h e c o o p e r a t i o n b e t w e e n Italian institu tions a n d the D e m o c r a t i c R e p u b l i c of C o n g o via t h e United Nations h a s pro d u c e d a m o d e r n monitoring network a n d a system of t e c h n i c a l a n d scientific relation ships that have improved the c a p a b i l i t y of GVO for v o l c a n i c s u r v e i l l a n c e, v o l c a n i c hazard evaluation, a n d risk a s s e s s m e n t at Nyiragongo a n d Nyamulagira v o l c a n o e s. T h e installation of t h e s e i s m i c network h a s b e e n simplified by t h e availability of wellp r e p a r e d sites a s well a s by the qualifica tion a n d d e d i c a t i o n of GVO staff. Visits by GVO r e s e a r c h e r s to Italian r e s e a r c h institu tions and v i c e versa a r e fostering further c o l l a b o r a t i o n a n d t h e planning of future i m p r o v e m e n t s to t h e monitoring in G o m a. S i n c e the J a n u a r y eruption, the n e w skills a n d c a p a b i l i t i e s of GVO p e r s o n n e l have a l l o w e d t h e m to survey continuously the two a c t i v e v o l c a n o e s in the D e m o c r a t i c R e p u b l i c of C o n g o, a n d their ability to monitor the v o l c a n i c activity and r e a c t to impending h a z a r d s h a s a l s o improved. Regardless of the history of strong vol c a n i c activity, most donors and a g e n c i e s within the United Nations unfortunately con sider the volcanic crisis in the D e m o c r a t i c Republic of Congo to b e over b e c a u s e of a lack of (volcanic) activity outside the crater within the past few years. Despite dramatic shortages of funds, though, several other Fig. 3. (left) Map of the city of Goma illustrating the susceptibility to lava flow invasion for flows arriving from the North, (right) Predicted paths of lava flows from the further extension of the main eruptive fissure system of January. Original color image appears at the back of this volume. projects are now under way to better monitor volcanic hazards in the area. Author Information D.Tedesco, Department of Environmental Sciences, University of Napoli,Caserta,Italyand CNR-IGAG Rzale Aldo Moro, Rome; dtedesco@unina.it; L. Badiali and E. Boschi, Istituto Nazionale di Geofisica evulcanologia,rome;ppapale,istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy; ETassi and O. Vaselli, Department of Earth Sciences, University of Firenze, Florence, Italy; C. Kasereka and J. Durieux, Goma Volca no Observatory Goma, Democratic Republic of Congo; G. DeNatale, Osservatorio Vesuviano, Istituto Nazionale di Geofisica e Vulcanologia, Naples, Italy; A. Amato and M.Cattaneo, Istituto Nazionale di Geofisica e Vulcano logia, Rome; H. Ciraba, Goma Volcano Observatory; G. D. Chirico, Istituto Nazionale di Geofisica e Vulcanologia, Pisa, and Department of Earth Sciences and Environ mental Geology University of Bologna, Italy; A. Delladio and M. Demartin, Istituto Nazionale di Geofisica e Vulcanologia, Rome; G. Favalli, Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy; D. Franceschi and VLauciani, Istituto Nazionale di Geofisica e Vulcano logia, Rome; G. Mavonga, Goma Volcano Observatory; G. Monachesi, N. M. Pagliuca, and D.Sorrentino, Istituto Nazionale di Geofisica e Vulcanologia, Rome; and M. Yalire, Goma Volcano Observatory

4 Eos, Vol. 88, No. 6,7 April 7 X + Fig.. (a) Map of Nyiragongo and Nyamulagira volcanoes. Seismic stations, marked as black dots, are located in sites that are both efficient and safe, (b) A local earthquake that occurred on 5 November. (c) A regional earthquake that occurred in Tanzania on November 3 (:3:8.69 ML.3 also in ISC), (d) A teleseism from Sumatra on 5 July (:3:9.9 ML 7. CSEM 69993). Page 77

5 Eos,Vol. 88, No. 6,7 April C (mmoi) C H (mmoi) Fig.. Chemical and isotopic profiles have been constructed for sites A and B (blue dots in figure J), located in Lake Kivu. Examples of (a) carbon dioxide (CO^ and (b) methane (CHJ profiles from one of the several chemical, isotopic, and physical studies carried out at Lake Kivu. Green dots represent data collected from site A (Kivu Lake) in Figure la and red circles from site B (Kabuno basin). Fig. 3. (left) Map of the city of Goma illustrating the susceptibility to lava flow invasion arriving from the North, (right) Predicted paths of lava flows from the further extension main eruptive fissure system of January. for flows of the