Nyiragongo especially, has been subject to much attention because of a pit crater within a 3,600ft deep caldera with an active lava lake. This appeared in 1928 but in 1977 a flank emission of lava drained the lake killing 70 people. Since 1982 the lava lake has built up again. Haroun Tazieff, the well-known volcanologist, has made an especial study of this mountain. The rocks of the region are variously described as potassic basanites, leucite basalts or leucite nepheline melilite basalts.
Stress is laid on their variability in different centres.
The nepheline is usually potassic and may be kalsilite. In fact the basanites appear similar to those of Tristan or Gough Islands. Melilite is usually found only in high Ca rocks. East Virunga Province. The fingerprint shows a negative K, a sure sign of a sodic magma though the level of LILE is very high.