Report on Nyiragongo (DR Congo) — October 2002

Bulletin of the Global Volcanism Network, vol. 27, no. 10 (October 2002)
Managing Editor: Richard Wunderman

Nyiragongo (DR Congo) New fissure vents and lava fountains; largest regional earthquake in 30 years

Please cite this report as:

Global Volcanism Program, 2002. Report on Nyiragongo (DR Congo). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 27:10. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN200210-223030.

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Nyiragongo

DR Congo

1.52°S, 29.25°E; summit elev. 3470 m

All times are local (unless otherwise noted)


An expedition visited the summit of Nyiragongo during 17-18 May 2002 to look for possible extrusive activity (BGVN 27:05). During the visit, a small lava fountain was observed on the floor of the crater.

A team ascended to the summit by foot during 16-17 July 2002. As they climbed the team first observed a gray-black plume at 2,700 m elevation, and began to clearly smell SO2 at 3,100 m. From the crater rim (3,425 m) the inner crater was only partially visible because of dense fog and the dark plume. Sounds of molten lava (fountains and spatters) falling on rocks were heard. Despite the extremely poor visibility, it was possible, around 0600, to witness some lava fountaining. The height was estimated as 100 m above the crater floor. During the night, a continuous and strong ashfall affected the upper part of the volcano. On the morning of 17 July the ashfall had ended and only a white plume exited the crater. It was clear that the lower and central part of the crater was extremely active and the presence of a new lava lake was suspected.

On 20 July, the Goma Volcano Observatory (GVO) reported that during the previous weeks, episodes of tremor (some lasting for 23 hours per day) were recorded on several seismic stations around the volcano. Because of poor atmospheric conditions, no helicopter flights were organized. From very limited views through clouds, a white to gray plume was suspected to rise above the crater.

A series of Nyiragongo crater observations were made in September and October of 2002. During 29-30 September the level of the bottom of the crater was stable and occupied by accumulated debris. The crater also contained several vents, the largest of which continued to eject gases at very high pressure. The red coloration of the plume at night was attributed by the GVO to Strombolian explosions and combustion of gases. Burned plants were seen on the crater's E side. An 8 October flight found the crater to be entirely filled by visible vapor as a result of magma degassing. An 11 October flight revealed a new crack at the top of Nyiragongo (at 01°36.840' S and 029°14.505' E), trending in an E-W direction. Scientists conducted gas measurements on 12 October on the ground at Kibunga (Binza); the sampled gases lacked indications of deep origin.

Dario Tedesco indicated that during the two nights preceding a large earthquake on 24 October (see "Regional seismicity" below), incandescence was visible above Nyiragongo's crater from Goma. Witnesses also reported that around this time they saw projections of incandescent lava rising above the crater's confines (perhaps signifying a particularly intense episode of lava fountaining).

Regional seismicity. During 29 September-5 October, GVO noted a slight decrease in high-frequency (HF) and a strong increase in long-period (LP) seismicity compared to mid-August. Specifically, a total of 260 HF and 1,024 LP earthquakes occurred during the week (compared to 290 HF and 287 LP events during 18-24 August). Volcanic tremor was registered at all seismic stations (except in Lwiro), consistent with the eruption at Nyamuragira and a gas plume at Nyiragongo. The tremor was slightly less significant at Nyamuragira (Katale station) than at Nyiragongo (Rusayo station). The spatial distribution of the epicenters revealed that the LP earthquakes were mostly located in the vicinity of Nyamuragira. In contrast, HF epicenters were dispersed, occurring both in the N, at Virunga and Masisi, and in the S, at Lake Kivu. Located magmatic and HF earthquakes tended to be distributed to the E of Nyamuragira and Nyiragongo, at depths of 5-15 km. Tremor, practically constant in amplitude, duration (several hours per day), and temporal distribution, registered at Katale and Rusayo stations. The tremor was taken to indicate great activity at Nyamuragira and Nyiragongo. At each volcano, there was a negative correlation between the abundance of tremor and presence of LP swarms.

During 6-12 October, GVO noted a total of 342 HF and 996 LP earthquakes. Magmatic and HF earthquakes at Nyamuragira and Nyiragongo yielded hypocenters at 5-20 km depths. Other observations of seismicity were similar to the previous week.

A tectonic earthquake was felt in Goma and surrounding areas on 8 October 2002. The region had been the scene of an unusual number of recent earthquakes (table 4). The U.S. Geological Survey's National Earthquake Information Center (NEIC) catalog for 2002 included an anomalously large swarm of tectonic earthquakes in the area, including many events over M 4 during January 2002. Epicenters in the January swarm were commonly within 50 km, and in one case 6 km, of Nyiragongo. The 8 October earthquake mentioned above is absent from table 4, perhaps because of insufficient magnitude or depth.

Table 4. A list containing all earthquakes of M 2 or greater within 200 km of Nyiragongo during 1 January 2002-26 November 2002. Bulletin editors accessed these data on the US Geological Survey's NEIC website using their catalog of historical and preliminary data. Bruce Presgrave (NEIC) first brought the anomalously large number of earthquakes in January 2002 to our attention.

Magnitudes include mb, Ms, Mw, and Mn; all are computed magnitudes for the earthquakes (where available). The moment magnitude Mw is a preferred magnitude scale for large earthquakes; it is in common use, computed from a long-period body- and mantle-wave moment tensor-inversion method. The surface-wave magnitude, Ms, gets computed from the vertical component of surface waves of 20-second period. Ms does not increase beyond magnitude 8, and thus indicates smaller values than some other magnitude scales for large earthquakes (not a big factor here). The body-wave magnitude, mb, gets computed using short-period P waves. The term mb has been used since the 1950's, but for large natural earthquakes it is generally less uniform and reliable than the moment magnitude (Mw). The term Mn may be less familiar. It is sometimes calculated for North America E of the Rocky Mountains, or other parts of the world using different calibrating functions. Mn is computed from the vertical component of 1-second Lg seismic-waves (short-period surface waves), and some workers label it MbLg.

[Skip text table]
    Date              Coordinates            Magnitudes            Radial
                   (decimal degrees)     mb   Ms  Contributed   distance (km)

    04 Jan 2002    0.136°S, 29.758°E    4.8  4.5      --            162
    17 Jan 2002    1.629°S, 29.152°E    4.3   --    4.30 Mn          16
    17 Jan 2002    1.684°S, 29.077°E    4.7   --    4.90 Mn          26
    18 Jan 2002    1.578°S, 29.031°E    4.2   --    4.70 Mn          25
    18 Jan 2002    1.780°S, 29.076°E    4.3   --    4.70 Mn          34
    18 Jan 2002    1.662°S, 28.866°E    4.2   --     --              45
    19 Jan 2002    1.761°S, 28.969°E    3.9   --    4.40 Mn          41
    19 Jan 2002    1.931°S, 29.579°E    4.6   --    4.70 Mn          58
    19 Jan 2002    1.879°S, 29.059°E    4.2   --    4.40 Mn          44
    20 Jan 2002    1.681°S, 28.981°E    4.9  4.6    5.20 Mn          34
    20 Jan 2002    1.641°S, 29.042°E    3.9   --    4.40 Mn          26
    20 Jan 2002    1.599°S, 29.050°E    4.2   --    4.60 Mn          23
    20 Jan 2002    1.726°S, 29.168°E    3.8   --    4.20 Mn          24
    21 Jan 2002    1.726°S, 28.854°E    4.6   --    4.90 Mn          49
    21 Jan 2002    1.505°S, 28.941°E    4.2   --    4.50 Mn          34
    21 Jan 2002    1.776°S, 29.041°E    4.9  4.5    5.10 Mn          36
    21 Jan 2002    1.903°S, 29.117°E    4.7   --    5.10 Mn          44
    22 Jan 2002    1.787°S, 28.971°E    4.0   --    4.30 Mn          42
    22 Jan 2002    1.746°S, 29.095°E    3.9   --    4.50 Mn          30
    22 Jan 2002    1.515°S, 28.993°E    4.9  4.7    5.20 Mn          28
    22 Jan 2002    1.551°S, 28.995°E    4.4   --    4.70 Mn          28
    22 Jan 2002    1.461°S, 29.249°E    4.2   --    4.60 Mn           6
    30 Jan 2002    1.633°S, 28.886°E     --   --    4.60 Mn          42
    11 Feb 2002    1.386°S, 29.010°E    4.4   --      --             30
    09 Sep 2002    2.567°S, 28.867°E    4.5   --      --            123
    24 Oct 2002    1.899°S, 28.904°E    5.8  6.3  6.10-6.20 Mw       56
    24 Oct 2002   -1.988°S, 28.875°E    5.3  5.5    5.50 Mw          66


A violent earthquake (Mw 6.1-6.2), one of the two largest in at least 30 years in this area, occurred at 0808 on 24 October (table 4). GVO reported that it was felt in surrounding areas, including Rutshuru, Goma, Bukavu, Butare, Kigali, and Bujumbura. GVO's seven operating seismic stations (Lwiro, Goma, Kunene, Katale, Kubumba, Rusayo, and Bulengo) recorded the earthquake but the high amplitude of the signals caused saturations, thwarting attempts to use local data to obtain rapid, meaningful solutions for seismic parameters. A second large-magnitude event (Mw 5.5) occurred about an hour later. Both earthquakes struck SW of Nyiragongo, at distances of 56 and 66 km (tables 4 and 5).

Table 5. A list containing earthquakes of M 5 or greater located within 300 km of Nyiragongo during 1 January 1973-26 November 2002. Earthquake depths were typically ~ 10-33 km. Editors accessed these data on the U.S. Geological Survey's NEIC website using the catalog of earthquakes located by the NEIC and its predecessors. See the caption for table 4 for a discussion of the magnitude determinations.

[Skip text table]
    Date              Coordinates            Magnitudes            Radial
                   (decimal degrees)     mb   Ms  Contributed   distance (km)

    21 Nov 1973    3.607°S, 28.186°E    5.1   --      --            258
    25 Apr 1974    0.995°N, 30.091°E    5.0   --      --            292
    06 Jan 1977    2.509°S, 28.702°E    5.3   --      --            124
    14 Apr 1977    2.456°S, 28.940°E    5.2   --      --            108
    29 Dec 1977    0.013°S, 29.683°E    4.8  5.4      --            175
    29 Jan 1978    3.929°S, 29.350°E    5.3   --      --            266
    25 Oct 1979    3.412°S, 29.070°E    5.2   --      --            209
    09 Jan 1980    3.445°S, 27.442°E    5.0  4.6      --            292
    21 May 1981    2.698°S, 28.661°E    5.0   --      --            145
    20 Jul 1981    2.709°S, 28.461°E    5.0  4.0      --            157
    09 Jan 1982    1.671°S, 28.338°E    5.0   --      --            102
    03 Jul 1982    3.737°S, 28.951°E    5.2   --      --            246
    04 Jul 1982    3.778°S, 28.917°E    5.0   --      --            251
    15 Jan 1983    0.513°N, 30.199°E    5.2  4.1      --            247
    24 Sep 1983    1.563°S, 28.381°E    5.2   --      --             96
    04 Sep 1990    0.479°S, 29.085°E    5.0  5.0      --            116
    18 Sep 1990    4.060°S, 29.483°E    5.0  4.3      --            281
    05 Feb 1994    0.593°S, 30.037°E    5.8  6.0    6.20 Mw         249
    29 Apr 1995    1.315°S, 28.605°E    5.1  4.9      --             75
    24 Mar 1996    0.565°N, 30.169°E    5.0   --    5.40 Mw         251
    02 Mar 2000    2.582°S, 27.826°E    5.4  4.5      --            196
    02 Mar 2000    2.371°S, 28.026°E    5.0  4.1      --            165
    29 Jun 2001    0.292°N, 29.972°E    5.0  4.4    5.30 Mw         215
    20 Jan 2002    1.681°S, 28.981°E    4.9  4.6      --             34
    21 Jan 2002    1.776°S, 29.041°E    4.9  4.5    5.10 Mn          36
    21 Jan 2002    1.903°S, 29.117°E    4.7   --    5.10 Mn          44
    22 Jan 2002    1.515°S, 28.993°E    4.9  4.7    5.20 Mn          28
    24 Oct 2002    1.899°S, 28.904°E    5.8  6.3  6.10-6.20 Mw       56
    24 Oct 2002    1.988°S, 28.875°E    5.3  5.5    5.50 Mw          66

Soon after the earthquakes, a GVO team measured the temperature and composition of gas released from fractures on the S flank of Nyiragongo and along the N shore of Lake Kivu. No significant changes were found with respect to the measurements taken in the previous days.

Damage was reported at Bukavu (fissures in house walls), Lwiro (some houses destroyed, roof of the seismic station collapsed, and walls of laboratories fissured), Mugeri (a church destroyed), Goma (several house walls fissured, and a truck accident killed two people), and Kigali (walls of several houses fissured, and a school wall collapsed, causing panic).

Since earthquakes commonly occur and are expected to occur again in the future in the active rift, GVO recommended an education campaign discussing seismic hazards and response related to Africa's Great Lakes region.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. In contrast to the low profile of its neighboring shield volcano, Nyamuragira, 3470-m-high Nyiragongo displays the steep slopes of a stratovolcano. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: Kavotha Kalendi Sadaka, Celestin Kasereka, Jean-Pierre Bajope, Mathieu Yalire, and Paolo Papale, Goma Volcano Observatory, Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo (Email: ocha.volcan@wfp.org); Jacques Durieux, Dario Tedesco, and Jack Lockwood, Groupe d'Etude des Volcans Actifs, 6, rue des Razes, 69320 Feyzin, France (Email: jdurieux@chello.fr, dtedesco@unina.it, jpl@alumni.princeton.edu); Bruce Presgrave, National Earthquake Information Center, P.O. Box 25046, MS 966, Lakewood, CO 80225, USA (URL: http://neic.usgs.gov/, Email: presgrave@neis.cr.usgs.gov); United Nations Office for the Coordination of Humanitarian Affairs (OCHA), United Nations, New York, NY 10017, USA (URL: http://www.reliefweb.int).