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.