Field of Science

Nyamuragira and Nyiragongo: History of two dangerous volcanoes

Many active, dormant and extinct African volcanoes are like the pearls of a necklace located along the Great Rift Valley, an active rift which almost splits Africa in half.

It's in the mid position of this rift-system, near lake Kivu, that the most active and dangerous African volcanoes can be found, the Nyiragongo (3.469m) and the Nyamuragira (3.085m). The Nyamuragira erupted between 1894 and 1979 for fifteen times (and is still active) forming large lava-streams (well recognizable on satellite imagines), however not affecing a densely populated area. In contrast the last eruption of the Nyiragongo in the Democratic Republic of Congo in January 2002 killed more than 100 people and caused great havoc in the nearby city of Goma - a foreseen catastrophe.

Fig.1. Igneous provinces of the Great Rift Valley (modified after U.S. Geological Survey, 2002).

The Nyiragongo, or mother of Gongo, after a spirit said to be living on the mountain, became famous for the lava lake in his 400m deep crater that persisted from 1927 until 1977. In 1958 an expedition by the Centre National Volcanologique Belge explored the lake, and after bypassing two platforms of solidified lava, the former surface of the lake, they analyzed the petrological composition of the peculiar basaltic lava, characterized by the presence of Leucite and Nepheline (minerals that from in lava with low silica-value) and measured a temperature of 1025-1095°C.

Fig.2. Simplified geological map with main lava-streams (name/year of formation from historic events) of the region of Nyamuragira (lava-deposits of this volcano yellow-orange) and Nyiragongo (blue-violet-red) projected on a satellite imagine (modified after PICHLER 2007, satellite imagine acquired in December 11, 2001 by NASA).

In 1964 the lava lake slowly begun to rise, and on January 10, 1977 a fissure opened on the flanks of the volcano. The very fluid lava reached a velocity of 15 to 60km/h, many villages were destroyed and on the street to the city of Goma the lava flow overtook and killed a group of peasants. The estimated number of victims ranges from a minimum of 72 to some hundred killed people.

After the eruption the volcanologist Maurice Krafft discovered in the solidified lava on the flanks of the Nyiragongo large hollows. After breaking apart some of them it was discovered that these hollows were the moulds of elephants and humans, killed and engulfed by the lava.

Fig.3. Mould and bones of an elephant, photo taken by Maurice Krafft after the eruption of 1977 (KRAFFT 1990, this image is taken from DECKER & DECKER 1992). The very fluid lava (with low silica content) killed and engulfed a small herd of elephants.

On June 21, 1982 a new lava lake begun to form in the crater and after three months it reached a level of 400m above the former ground. Until 2001 this new lake experienced various fluctuations, and between June and October 1982 the volcanic activity increased, despite this the eruption affected only the inside of the crater, until 2002.

In 2001 the high lake level aroused preoccupation, and it was expected that like before the flanks of the mountain would collapse - in January 2002 a new fissure opened near the old ones, diverging the lava in direction of the airport and the city of Goma.
The city was caught unprepared, and thousands of inhabitants fled in panic, it wasn't even attempted to diverge the lava flows by earth-dams.
The missing political awareness, the fail of mitigation measurements and the missing monitoring program of such a dangerous volcano, practically inexistent since 1985, led to this avoidably catastrophe, and is unfortunately a direct result of the chaotic political situation in this part of Africa.


Bibliography:

DECKER, R. & DECKER, B. (1992): Vulkane. W.H. Freeman & Company, New York - Oxford: 267
KRAFFT, M. (1990): Führer zu den Virunga-Vulkanen. Enke-Verlag, Stuttgart: 187
PICHLER, T. (2007): Vulkangebiete der Erde. Spektrum Akademischer Verlag, München: 261

2 comments:

  1. when was the Nyamuragira volcano formed

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  2. when was the Nyamuragira volcano formed

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