January 2002 volcano‐tectonic eruption of Nyiragongo volcano, Democratic Republic of Congo

Abstract

In January 2002, Nyiragongo volcano erupted 14–34 × 106 m3 of lava from fractures on its southern flanks. The nearby city of Goma was inundated by two lava flows, which caused substantial socioeconomic disruption and forced the mass exodus of the population, leaving nearly 120,000 people homeless. Field observations showed marked differences between the lava erupted from the northern portion of the fracture system and that later erupted from the southern part. These observations are confirmed by new 238U and 232Th series radioactive disequilibria data, which show the presence of three different phases during the eruption. The lavas first erupted (T1) were probably supplied by a residual magma batch from the lava lake activity during 1994–1995. These lavas were followed by a fresh batch erupted from fissure vents as well as later (May–June 2002) from the central crater (T2). Both lava batches reached the surface via the volcano's central plumbing system, even though a separate flank reservoir may also have been involved in addition to the main reservoir. The final phase (T3) is related to an independent magmatic reservoir located much closer (or even beneath) the city of Goma. Data from the January 2002 eruption, and for similar activity in January 1977, suggest that the eruptive style of the volcano is likely to change in the future, trending toward more common occurrence of flank eruptions. If so, this would pose a significant escalation of volcanic hazards facing Goma and environs, thus requiring the implementation of different volcano‐monitoring strategies to better anticipate where and when future eruptions might take place.

Magma sources involved in the 2002 Nyiragongo eruption, as inferred from an InSAR analysis

“…The presence of the deep dike could have facilitated the connection between the deep dike and the southern part of the shallow dike, leading to the eruption of magma from the deep source south of the eruptive fissure. This scenario involving the lava lake, a shallow reservoir and a deep reservoir for the southernmost fissure is consistent with the geochemical analysis and model of Tedesco et al [2007].…”

“…[57] The model is also consistent with 38 U and 232 Th series radioactive disequilibria data, calculated from lavas emitted during the eruption [Tedesco et al, 2007], which suggest that the eruption was fed by up to three different magmatic sources. These authors infer that the northern lava flows were probably supplied by the lava lake and a shallow magma reservoir, while the southern lava flows were related to a second, deeper reservoir, probably located beneath Goma city and Lake Kivu.…”

“…Between 4 and 16 January 2002, and after the effusive activity had stopped, seismic activity remained high [Kavotha et al, 2002[Kavotha et al, /2003]. About 100 tectonic earthquakes with magnitudes greater than 3.5 were recorded in the five days following the eruption over the whole Lake Kivu area [Tedesco et al, 2007], culminating in a 6.2 M w event on 24 October, 2002 [Mavonga, 2007]. Although the seismic network was not capable of accurately determining the location of the seismic events, they generally cluster along the faults on the western side of the Kivu basin, as found for previous recorded events [Zana and Hamaguchi, 1978;Mavonga, 2007].…”

“…Durieux, personal communication, 2005). These measurements were repeated at irregular intervals until March 2002 [Komorowski et al, 2002[Komorowski et al, /2003Tedesco et al, 2007] and showed an asymmetric increase in the water level of Lake Kivu, which reached a maximum of about 37 cm at the Goma shore (Profile A in Figure 3). Due to the agitation of the water surface by waves, and given possible additional sources of perturbations such as water discharge at the 100 km-distant Ruzizi hydroelectric dam, seasonal effects, seiches, etc., uncertainties can conservatively be estimated to be of the order of 30 cm.…”

“…14-34 c [Tedesco et al, 2007] 1977 155 [Tedesco et al, 2007] 234 [Tazieff, 1977;Komorowski et al, 2002Komorowski et al, /2003 212 d [Tazieff, 1977;Komorowski et al, 2002Komorowski et al, /2003 22 c [Tazieff, 1977;Komorowski et al, 2002Komorowski et al, /2003 a The crater rim is located at 3,425 m above sea level. b Estimated from the volume drained from the crater lava lake.…”