ERUPTION ALERT – Nov.-Dec. 2011 eruption of Nyamulagira
Information report n°6 – 7th December, 2011
Nyamulagira volcano has started to erupt on 6th November 2011, 5:55 PM (UTC+2). This eruption is located ± 12 km east-northeast of the Nyamulagira crater, close to one of the 1989 eruptive sites. The previous eruption of this volcano occurred 22 months earlier, in January 2010. The eruptive fracture is oriented approximately East-West, perpendicularly to the rift direction. After a week of eruption, the lava flows reached their maximum length of ~11.5 km.
Information from optical satellite imagery
Optical images acquired during the second half of November 2011 do not allow a good observation of the Nyamulagira eruption due to important cloud cover. The Landsat 7 ETM+ image acquired on 21st November 2011 shows that the lava flow did not grow in length, but widened and developed new branches (Fig. 1).
Information from SAR satellite imagery
A new ENVISAT-ASAR radar image was acquired on 2nd December 2011. Comparison between pre- and post-eruptive radar images allowed us detecting and mapping part of the new lava flow, where it overlap the former 1989 lava flow (Fig. 2). A second branch is detected in the northern half part of the flow and a third smaller one has developed on the western side of the main flow (pink arrows on Fig. 3).
The surface change which is linked to the presence of the lava flow represents an area of about 14.7 x 106 m². Assuming a mean thickness of 3 m, a common value for Nyamulagira, the estimated corresponding volume of lava is ~44 x 106 m³. This estimation based on coherence images only refers to part of the new lava flow that overlaps the former 1989 lava flow and is therefore underestimating the actual volume of the ongoing eruption.