November 2011 eruption

ERUPTION ALERT – November 2011 eruption of Nyamulagira
Information report n°5 – 15th November, 2011

Eruption summary

On 6th November 2011, 5:55 PM (UTC+2), Nyamulagira volcano has started to erupt after two days of intense seismic activity. 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.

Figure 1 – Picture of the 2011 eruptive site of Nyamulagira volcano.

Information from optical satellite imagery

ASTER, Hyperion and ALI images were acquired on November 12 and allow for the first time estimating the length of the lava flow. Within 6 days of eruption, the lava flow reached 11.5 km long. The path followed by lavas corresponds to the most western one suggested by the lava flow simulations (Fig. 2 and 3). On November 12, the lava flow front was located 5 km far from the road Kelengera-Tongo. According to the lava flow simulations, this road could be threatened by the lava flow.

Figure 2 – Probability of invasion by lavas (log) for a ±20 km long and 3 m thick lava flow (5000 iterations). The black lines show the paths currently followed by the lava flows until November 12. (c) B. Smets, RMCA, 2011

Figure 3 – Map with a sketch of the ALI image acquired on 12/11/2011. After 6 days of eruption, the lava flow length reached 11.5 km long. At the date of the image acquisition, the lava flow front was 5 km far from the Kalengera-Tongo road. The red circle on the map highlights the threatened part of this road according to the lava flow simulations. (c) B. Smets, RMCA, 2011

Information about ground deformations

Satellite radar images acquired on November 11 revealed major ground deformation features associated to the eruption. It is actually the largest deformation ever detected by that method (InSAR) since the early 1990’s over that volcano.
Very preliminary estimation of the observed deformation signal suggest an affected area spreading over much more than 250 km2.
Under the pressure of the ascending magma, the ground rose up to more than 50 cm at the eruptive site where the spatter cone is developping. Another 15 cm deformation is detected within the Nyamulagira caldera accompanied with a deflation observed on the flanks. In contrast, no apparent deformation can be noticed on Nyiragongo until that image acquisition.

More detailed analysis is under way and additionnal satellite images are due for the coming days.

The GORISK scientific network would like to thank A.G. Davies1, D. Pieri1 and G. Vaughan2 for their help in acquiring ASTER, Hyperion and ALI images. A special thank to Sergey Samsonov3 for the production of the first SAR interferogram of the eruption.

1- Jet Propulsion Laboratory, USA
2- U.S. Geological Survey, USA
3- Canada Center for Remote Sensing, Canada