VII. International Activity

1. Cooperative Observation of Volcanic Activities at Nyiragongo and Nyamuragira Volcanoes in Africa

Nyiragongo volcano standing at the northern edge of lake Kivu in the western rift valley was nominated as the African Decade Volcano by IAVCEI. This volcano is characterized by the existence of a persistent lava lake. This is the rare case of long-lived activity within one open vent. Though the lava lake in the summit crater had been dormant since 1982, it was rejuvenated on June 23, 1994. Almost simultaneously, the population of refugees fleeing from the neighboring countries had abnormally increased in the volcanic area where the potential hazardous condition had been enhanced. The geophysical monitoring of volcanic activity has been urgently carried by the joint team of Goma Volcano Observatory of CRSN, Rep. Dem. of Congo and Tohoku University, Japan. The observation was initially supported by UNHCR and the Japanese Government. However, it is unfortunate that all monitoring stations operated around the volcano were completely destroyed in October 1996 when a huge throng of refugees started all at once to return to their home countries. Since then, instrumental monitoring in and around the Nyiragongo volcanic area had been dead completely. The variation of the lava lake level in the summit crater has been monitored intermittently by using the EDM method. The surface of lava lake rose by 110 m during the period from August 1994 to September 1996 and is now located about 120 m below the first terrace. The supplied magma volume in this period was estimated to be about 1.3 x 10**8 m**3. Activity of volcanic tremor events terminated in August 1996.

Nyamuragira volcano is located about 13 km northwest of Nyiragongo volcano. New eruption started on October 16, 1998. The newly created cone called "Mapambone" was located at the NW flank of the summit, close to Ndakaza and Shabubembe cones that erupted in November 1951. Huge amount of fluidal basaltic lava was emitted and two lava flows were witnessed by local people: one flow was about 18 km in length toward the west and the other was abour15 km toward the north. The eruptive activity stopped on October 26, 1998.

(Hiroyuki Hamaguchi)

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