The third geophysical survey of Nyiragongo which lava lake appeared on June 21, 1982.

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The results obtained by the third geophysical survey in Virunga volcanic region, Zaire, are summarized as follows. (1) The lava lake of Nyiragongo was observed to increase in amount of furmarole without temperature change. (2) Seismic activity in 1988 was high at the southeast of Nyamuragira crater, where new eruptions took place in April, 1989. (3) The expansion of Nyamuragira crater reached to a value of 1x10^<-4> in strain after the 1989 eruption. (4) By the magneto-telluric method, a high conductive area being interpreted as partial melting part was found to be along a narrow zone of old eruption places. (5) Aphyric type elements of ejecta from the 1975-1989 Nyamuragira eruptions changed to mafic with time, increasing in amount of MgO, CaO and decreasing in K_2O and Na_2O.