The Virunga volcanoes in D. R. CONGO

The main objective of this work is to present a description of the precursory phenomena of the volcanic eruptions of two active volcanoes Nyiragongo and Nyamulagira. The volcanism of Virunga, like the whole volcanism in the divergence zones, is the Hawaiian type characterized by a passive overflowing of basaltic magma, i.e., very fluid and at very high temperature. The source data for our study are the earthquake data collected in the stations installed around the active volcanoes and that of Lwiro located at about 90 Km away of Virunga region. The discrimination in frequency content of earthquake leads to the classification of volcanic earthquake in 3 classes or types, namely: A-type, B-type and C-type earthquake to which are added the volcanic tremors. The identification of volcanic earthquakes and the associated parameters and the collateral phenomena made possible to group the precursors of volcanic eruptions in 3 classes which are remote, close and imminent precursors. The impact of the activity of the one of the two volcanoes to on another has been established as well as that of the tectonic activity of the Western Branch of the Rifts on the Nyiragongo.