The eruption has been initiated by 3 different fractures, or fractures systems, on July 25th, at 03.30 pm, local time. One fracture was open in the central caldeira : lava flows have covered a major part of the floor and partially filled the pit crater (Crater B).
Another fracture was active on the South flank, with lava fountains and one lava flow traveling towards the S-W. This fracture has been active during the first hours of the eruption only ; extension of the lava flow is not known yet.
The fractures open on North flank extended for about 2 Km from the crater rim (2.959m) down to an altitude of approx. 2.540m. At the beginning of the activity, typical of Nyamuragira, lava fountains appeared along the fractures and important amount of spatters accumulated around it. Numerous lava flows (either pahoehoe and aa) have been emitted from several points of the fracture system, following the usual pattern of Nyamulagira eruptions.
On August 6th, only the lower part of the fracture was active : an important cone (several hundreds meters long, approx 70m high) contained 3 very active lava fountains ejecting scoriae at an altitude of about 100m. From a breach in the lowest part of the cone (South) a very fast moving lava flowed in the N-E direction; production rate of lava was estimated, at that time, to approx. 3 millions cubic-meters per day, which is the normal average for the volcano.
The activity of fountaining and lava emission regained some intensity at the beginning of the night, but later on, in the early morning August 7th dropped dramatically.
At that time, only one weak lava fountain remained active in the new crater. No correct estimations have been possible on the lava flow.
The decreasing activity has also been detected by the lowering of the tremor level recorded on the whole seismic nertwork of the GVO : low level tremor was predominant on the morning of August 8.
Due to poor weather conditions, but also due to the presence of non-desired journalists aboard the commercial GLBC helicopter, the planned flight above the entire lava flow of Nyamulagira and Nyiragongo was not made possible. Further flights with MONUC will allow to estimate the extension of the North lava flow of Nyamulagira and the possible activity inside Nyiragongo crater.
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