An exceptional eruption: Mt. Niragongo,Jan. 10th, 1977

The two westernmost volcanoes of the Virunga range (Zaïre Rep.) have just offered simultaneous eruptions. The volcano Niragongo delivered an exeeptionally short, yet important, eruption on 10 Jan. 1977. More than 20 × 10 m³ of molten melilite nephelinite were drained from the 3,270 m suspended lava-lake and spread over 20 km² in less than one hour. This put an end to the half-a-century old sub-permanent lava-lake activity which had rendered Niragongo known world-wide. This event happened during a flank eruption (the new Murara vent) of the close-by sister-volcano, Nyamlagira. This Murara event is quite similar to the many previous ones observed during the last 40 years. Neither of the two outbursts did have, even slightly, any detectable effect on each other. Yet, this simultaneity is probably not due to mere coïncidence.