November 2011 eruption

ERUPTION ALERT – Nov. 2011 – Apr. 2012 eruption of Nyamulagira
Information report n°7 – 6th June, 2012

Final summary

The last eruption of Nyamulagira volcano started on 6th November 2011, 5:55 PM (UTC+2) until April 2012. This eruption was located ± 12 km east-northeast of the Nyamulagira crater, close to one of the 1989 eruptive sites. A first fissure opened with a ~ East-West orientation, from which lava escaped, forming lava fountains and lava flows. After a week of eruption, the lava flows reached their maximum length of ~11.5 km. An elongated spatter-and-scoria cone (i.e. the western cone) formed along this fracture. In early December 2011, a new cone (the eastern cone) formed east to the first one, on a new eruptive fracture. The next days, the volcanic activity progressively migrated to this new volcanic edifice. During the 3 last months of the eruption, the eruptive activity was mainly represented by a temporary lava lake within the eastern cone. Lava flows were fed through lava tunnels, fresh lava being mainly visible during the night. The local population named the two new volcanic cones “Umoja” (western cone) and “Tuungane” (eastern cone). Our preliminary estimates for the 2011-12 eruption indicate a volume of emitted lavas of at least 81.5 x 106 m3. These lava flows did not reach inhabited areas and only affected the vegetation of the Virunga National Park.

Panoramic view of Nyamulagira volcano and the two cones of the 2011-12 eruption.

The previous eruption of Nyamulagira occurred 22 months earlier, in January 2010. The 2011-12 eruption is the biggest event of the volcano since the 1991-1993 eruption, which lasted nearly 1.5 years and emitted a lava volume estimated to ~ 131 x 106 m3 (Smets et al., 2010).

Starting from the end of February 2012, degassing occurred in the Nyamulagira’s caldera. The emission site is located inside the pit crater, but all fractures inside de caldera are degassing. On several occasions, sulfur smells reached the city of Goma due to unusual meteorological conditions.