Draining of Lava Lake in 1977 Eruption.
The lava lake drained out through a series of perpendicular (N-S and E-W)
fissures which broke open at altitudes up to approximately 2,200 m on the
nothern side of Niragongo, 2,400 on the western side and 2,700 m in the south. Observations showed that the lava lake drained completely in a hour, and most of it was gone in 30 minutes.
The lava flows were:
1. Murara lava flows. (W)
2. Mudjoga-Kibati-Minigi flows. (SSE)
3. Shaheru crater flow. (S)
4. Western Niragongo slope, fracture and flows.
5. Baruta-Mihaga fractures and northern flows.
To the north and west, two lava fows spread out, approximately 2 sq km each. The main flows ran sonthwards and southeastwards to more than 10 km from their origin covering an area about 18 sq km.
To the North and West, lava was poured out into deserted jungle, to the
South and East into populated areas. Several villages were wiped out, with 60 to 300 people were burnt alive. The main road linking Northern and Southern Kivu
province was cut over a length of 10 km. The eruption drained, 3 to 5 million cubic m of lava drained into the forest, on the northern and western slopes of the volcano. This prevented probably destruction of Goma and Gisenyi. (Note: the eruption in 2002 did not spare goma).
The 1977 crater was about 800 m deep ten days after the eruption. The fractures on the flanks of the volcano covered 20 km and had an average width of 10 m. An estimated volume of 50,000 cubic m of lava was expelled by the phreatomagmatic eruption which immediatelyfollowed the collapse of the inner parts of the crater.
Sequence of events for the eruption.
1) Ascent of magma followed by lava lake overflow.
2) Very fast draining of the lava-lake.
3) Almost immediate collapse of all the concentric large platforms inside the summit crater. Collapsed platforms contains groundwater which flashed to steam on contact with hot rock. A volcanic plume reached 35,000 ft altitude and was accompanied by roaring noise.
4) New ascent of magma into conduits drained through radial fissures.
According to eye-witnesses, lava flows reached the outskirts of Goma in 20 minutes, at a speed of 30 km/hr. Further uphill lava flowed at 60 km/hr, reaching 100 km/hr at the fracture point. Fast lava flows generated strong winds which unrooted eucalyptus trees and destroyed banana plantations.
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