Report on Nyamuragira (DR Congo) — December 1981
Scientific Event Alert Network Bulletin, vol. 6, no. 12 (December 1981)
Managing Editor: Lindsay McClelland.
Nyamuragira (DR Congo) Fissure eruption; lava flow and tephra column
Please cite this report as:
Global Volcanism Program, 1981. Report on Nyamuragira (DR Congo) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 6:12. Smithsonian Institution.
1.408°S, 29.2°E; summit elev. 3058 m
All times are local (unless otherwise noted)
A 400-m-long fissure opened before dawn 26 December in the saddle between Nyamuragira and Nyiragongo. The exact location of the fissure was not known at press time, but there are numerous old vents within the 14 km, NNW-trending rift zone between the two volcanoes. Activity began, probably at about 0130, with a strong explosion from the upper end of the fissure (at 2,300 m altitude) that ejected a 3-4 km-high tephra cloud. After the initial explosion, lava was extruded from the lower end of the fissure and flowed N. Residents fled the area. Images from the NOAA 7 satellite showed a large hot area between the volcanoes at 0230 on 27 December that had not been present 24 hours earlier. By the afternoon of 30 December, the lava flow was 15-20 km long, but only 300-400 m wide. Lava fountaining was continuing and a cone was growing at the vent. Tephra ejection was also continuing, preventing aircraft from flying near the active fissure, although it was not as vigorous as during the initial explosion.
Shallow earthquakes occurred 18 November at 1118 and 1234 at 2.11°S, 22.83°E and 2.22°S, 22.52°E, about 725 km ESE of Nyamuragira in an area that is not normally seismically active. Kampala Domestic Service reported a felt earthquake in the Bushenyi district of Uganda, ~150 km NE of Nyamuragira at 0300 on 30 December.
Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.
Information Contacts: M. Krafft, Cernay; M. Matson, NOAA; USGS/NEIS; Kampala Domestic Service, Uganda; WCBS Radio, USA.