Nyos, Monoun and Kivu : The Killer Lakes

17 Ottobre 2014

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    Nyos, Monoun and Kivu : The Killer Lakes





    They are located between Cameroon and the border between Rwanda and the Democratic Republic of Congo.
    The feature they have in common is that all three lakes are subject to limnic type eruption, also known as "overturning of the lake."
    This type of eruption is a rare type of natural disaster in which carbon dioxide (CO2) in solution suddenly erupts from deep lake water, suffocating wildlife and wild plants, livestock and humans. It can also cause a tsunami because the CO2 rise can cause rapid water movement in the lake and can be triggered by landslides, volcanic activity, or explosions. The lakes in the occurrence of this phenomenon may be known as limnically active lakes or explosive lakes.
    Characteristics of lakes limnically active, are,for example:
    CO2-saturated incoming water
    A cool lake bottom indicating an absence of direct volcanic interaction with lake waters
    An upper and lower thermal layer with differing CO2 saturations
    Proximity to areas with volcanic activity
    Scientists have recently determined, from investigations related to the large number of victims in the 80 'in Monoun Lake and Nyos Lake, that limnic eruptions and volcanic eruptions, although they are indirectly related, however, are catastrophic events of different types.

    Nyos Lake



    Nyos Lake correct


    It is located in the north-western Cameroon province , about 315 km north-west of Yaounde.
    It is a deep lake located in the crater of a dormant volcano in the massif of Mount Oku, in the line of volcanoes in Cameroon.
    A natural dam of volcanic rock enclosing the waters of the lake.
    A bag of magma lies beneath the lake causing the leakage of carbon dioxide (CO2) that saturate water.
    On August 21, 1986 night, the valley of the lake was hit by a natural disaster that killed more than 1,700 people in their sleep, as well as 3500 cattle heads. Initially, the representatives of the authorities arrived to investigate thought about a sudden issue of sulfur gas, being the area affected by volcanic activity, but later they verified that the victims were killed by a CO2 cloud. The phenomenon was linked to the similar, but much smaller scale, that happened at the lake Monoun two years earlier, and scientists were able to reconstruct the dynamics of disaster: a sudden event, probably a landslide, had moved the waters of the lake freeing dioxide dissolved carbon in them in large concentrations.
    It was noted that indigenous peoples considered the lake a place inhabited by murderer spirits, so none of the victims was from the area. Scientific investigations made ​​it possible to trace the causes of the phenomenon: the waters of Lake Nyos, two hundred meters deep, are affected by meromixis, (the physical condition of a body of water with a constant stratification. Practically surface water are not mixed with those in background, creating two overlaid lakes with different physical and chemical conditions.) and hold a huge amount of CO2 in solution; the surface layer of the lake, about fifty meters deep and fed mainly by rainwater and rivers, has no trade with the lowest layer of the lake which unlike the first presents an important anomaly: it is powered by a source of sodium carbonate which contributes to saturating the water with carbon dioxide. Given that in the point of greatest depth of the lake up to ten liters of anhydride per liter of water are dissolved , the eruption of 86 liberated into air eighty million cubic meters of gas.



    Some estimates have suggested that, following the 1986 limnic explosion limnica , the concentration of CO2 is returned to the levels prior to the disaster in 1992, and no precautions were taken to prevent a recurrence of the tragedy. The area surrounding the lake was evacuated by the Cameroon government in the following years and, to prevent a recurrence of the limnic eruption, in 2001 was installed a degassing system. It consists of a siphon that draws water from the bottom of the lake so as to cause a slow and steady gas leakage. Two additional tubes were installed in 2010.



    Un ulteriore potenziale elemento di rischio è dato dall'indebolimento della diga naturale di roccia che circonda il lago. Un suo crollo potrebbe causare la fuoriuscita dell'acqua del lago con effetti disastrosi sui villaggi circostanti. L'area stimata interessa circa 10.000 persone.

    Monoun Lake





    On August 15, 1984 in the lake took place that which was later recognized as a limnic type eruption, which caused an abundant emission of carbon dioxide (CO2) and as a result of which 37 people died of asphyxiation. The cause of mortality of people did not have an explanation, and it was initially assumed a terrorist act. Extensive investigations, deriving mostly from the next and most important event that occurred in Lake Nyos two years later, led to the death by asphyxiation of approximately 1,700 people in more than 3500 head of cattle, and led to the understanding of what had happened.


    Kivu Lake





    Lake Kivu is one of the great African lakes, situated on the border between the Democratic Republic of the Congo and Rwanda, at 1460 m asl It has an area of 2700 km ². Its waters house some islands and Idjwi Island, with its area of ​​340 km2, is the second largest lake island in Africa, after the island Ukerewe in nearby Lake Victoria.
    It has an emissary, the Ruzizi River, which carries its waters to the south to Lake Tanganyika.



    Like the other two lakes, Nyos and Monoun, the Kivu has been a limnic eruption. The analysis of the geological history of the Kivu shows that over the past millennia, there have been incidents of biological extinction. It is not clear the cause of these phenomena for the Kivu, but it is suspected that it is connected to volcanic activity.
    The chemical composition of lakes subject to limnic explosions is specific to each individual case, but in the case of the Kivu it seems to be tied to a mixture of carbon dioxide (CO2) and methane, instead of just CO2 as in the other two cases. Methane seems to come from microbial reduction of CO2 of volcanic origin. The impact of a massive eruption in the case of Kivu would be catastrophic, since the area of its basin is home to about two million people.



    Coring in the Bukavu Bay revealed in the lake bottom three layers interspersed with deposits of rare mineral monohydrocalcite with diatomaceous conglomerates, overlying sapropelic sediments with high content of pyrite. It is believed that the sapropelic sediments are derived from hydrothermal discharge while diatoms were the result of a bloom which reduced the concentration of carbon dioxide to a level that would allow the precipitation of monohydrocalcite.
    It is assumed that sufficient volcanic interaction with the water of the lake bottom is characterized by a high concentration of gas that may heat the water mass, release methane and trigger a nearly simultaneous release of carbon dioxide.

    The carbon dioxide thus released could lead to death by asphyxiation of a large number of people around the lake, but also trigger a tsunami connected to the explosion of the gas.


    *Attention please* - - "This translation (and / or content) is made by Sylvhia exclusively for "I Nove Mondi Forum". In case of partial or full release is mandatory to link to the original source and the required credits".




    http://it.wikipedia.org/wiki/Lago_Kivu

    http://it.wikipedia.org/wiki/Lago_Monoun

    http://it.wikipedia.org/wiki/Lago_Nyos
     
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0 replies since 17/10/2014, 21:12   185 views
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