Volcanic Activity- Lake Nyos

					Volcanic Activity-
Stage 1 Geology A, 2009




Lake Nyos
Helene McKie
                                  Stage 1 Geology A, 2009
                              Volcanic Activity Assignment
                                             Helene McKie




      Lake Nyos 2008


      Lake Nyos
     Max. Length- 2km
     Max. Width- 1.2km
     Max. Depth- 208m
Maar Formed- Approx. 1600CE
                                                                            Stage 1 Geology A, 2009
                                                                        Volcanic Activity Assignment
                                                                                       Helene McKie

Lake Nyos is a crater lake which lies within the Oku Volcanic Field on the northern boundary of the
Cameroon Volcanic Line, a zone of crustal weakness and volcanism. It is located in western
Cameroon, adjacent to Nigeria, in the elbow region of West Africa.




                                  Location of Lake Nyos in Cameroon.




                                  Location of Lake Nyos in the world.
                                                                              Stage 1 Geology A, 2009
                                                                          Volcanic Activity Assignment
                                                                                         Helene McKie




Though no information could be found on the tectonic setting of the Crater Lake, I surmise that it is
located in a subduction zone on a convergent plate boundary. I have come to this conclusion due to
the fact that Lake Nyos lies within the Oku Volcanic Field, which consists of Scoria (Cinder) cones and
Volcanic Maars. It also shares the same volcanic line as Mt. Cameroon, a stratovolcano.




                                       Cameroon Volcanic Line
                                                                                   Stage 1 Geology A, 2009
                                                                               Volcanic Activity Assignment
                                                                                              Helene McKie

The most famous “eruption” of Lake Nyos occurred on the night of the 21st of August 1986. A deadly
CO - rich cloud was expelled from the southern floor of the lake. The cloud, containing about 1.6
million tonnes of CO₂, rose at the rate of 100km/h and quickly enveloped houses located within the
crater, 120 metres above the shoreline of the lake. The cloud, which is thought to have been about
50 metres thick, then travelled downhill in a concentrated form for over 23km. As CO₂ is 1.5 times as
dense as air, humans and animals in the villages of Nyos, Kam, Cha and Subum and their
surroundings were deprived of oxygen. Most victims appeared to have simply fallen asleep and died
from asphyxiation. Many died in their beds.

One survivor, Joseph Nkwain of Subum was able to recount what had happened to him that night.

    "I could not speak. I became unconscious. I could not open my mouth because then I smelled
      something terrible . . . I heard my daughter snoring in a terrible way, very abnormal . . . When
    crossing to my daughter's bed . . . I collapsed and fell. I was there till nine o'clock in the (Friday)
   morning . . . until a friend of mine came and knocked at my door . . . I was surprised to see that my
  trousers were red, had some stains like honey. I saw some . . . starchy mess on my body. My arms
 had some wounds . . . I didn't really know how I got these wounds . . .I opened the door . . . I wanted
     to speak, my breath would not come out . . . My daughter was already dead . . . I went into my
  daughter's bed, thinking that she was still sleeping. I slept till it was 4:30 p.m. in the afternoon . . . on
  Friday. (Then) I managed to go over to my neighbours’ houses. They were all dead . . . I decided to
leave . . . . (because) most of my family was in Wum . . . I got my motorcycle . . . A friend whose father
 had died left with me (for) Wum . . . As I rode . . . through Nyos I didn't see any sign of any living thing
    . . . (When I got to Wum), I was unable to walk, even to talk . . . my body was completely weak."


The lethal cloud killed over 1700 people, thousands of cattle and many more bird and animals.
Following the eruption, many survivors were treated at the main hospital in Yaoundé, the country's
capital. Doctors found that many of the victims had been partially poisoned by the mixture of such
gases as hydrogen and sulfur. He described that poisoning by these gases would lead to burning
pains in the eyes and nose, coughing and signs of asphyxiation similar to being strangled, as like
"being gassed by a kitchen stove".




                 Lake Nyos after 1986 “Eruption”                              Dead Livestock
                                                                             Stage 1 Geology A, 2009
                                                                         Volcanic Activity Assignment
                                                                                        Helene McKie

There were no warning signs recorded before the expulsion of the CO₂- rich cloud. Two years earlier,
on August 15th 1984 a similar expulsion occurred thirty kilometres away at Lake Monoun, killing 34
people. US investigators concluded that this earlier event was caused by a landslide, an earthquake
or abnormally heavy rains. This, however, could not explain the “Eruption” of Lake Nyos as none of
the occurrences was recorded at the time. The only explanation was a “gas-rich volcanic eruption” in
which the gaseous bottom layers of the lake were somehow brought up to the surface.

Today, French scientists are working on degassing the lake. The method consists of a pipe set up
vertically between the lake bottom and the surface. A small pump raises the water in the pipe up to
a level where it becomes saturated with gas, thus lightening the water column; consequently, the
diphasic fluid rises to the surface.




          Diagram of method of degassing              “Fountain” formed when degassing in process


It has been suggested that the natural dam of volcanic rock that keeps in the lake’s water may
collapse in the near future. If the wall were to give way 50 million cubic meters of water would flood
downhill into areas of the Northwest Province and the Nigerian states of Taraba and Benue. It is
estimated this area is home to over 10,000 people. So far no measures have been taken to
strengthen the lake’s wall.

				
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Description: Volcanic Activity- Lake Nyos