The Exploding Lakes of Cameroon

　　What #es to mind when you think of a lake? You probably imagine a pretty scene with

　　blue water，birds，and fish．For the people in the northwestern Cameroon，however, the image is

　　very different.  For them，lakes may mean terrible disasters.  In 1984，poisonous gases exploded

　　out of  Lake Monoun and came down into the nearby villages，killing thirty—seven people．Two

　　years later,Lake Nyos erupted A cloud of gases rolled down the hills and into the valleys and

　　killed 1,700 people．

　　Lake Nyos and Lake Monoun are crater(火山口)lakes They were formed when water

　　collected in the craters of old volcanoes The volcanoes under Lake Nyos and Lake Monoun are

　　not active anymore.  However, poisonous gases from the center of the earth continue to flow up

　　through cracks in the bottom of the lake. This is normal in a crater lake. In most crater lakes，these

　　gases are released often because the water‘turns over’regularly．That is，the water from the

　　bottom of the lake rises and mixes with the water at the top，allowing the gases to escape slowly．

　　However，in Lakes Nyos and Monoun，there is no regular turning over．No one knows the

　　reason for this fact，but as a result，these lakes have more gases tapped at the bottom than other

　　crater lakes.  In fact，scientists who have studied Lakes Nyos and Monoun have found 16,000

　　times more gases．When a strong wind，cool weather a storm，or a landslide(滑坡)causes the

　　water to turn over suddenly，the gases escape in a violent explosion．

　　In the past，no one knew when the gases might explode，so there was no way for the villagers

　　to escape disaster.  Now scientists from the United States，France，and Cameroon have found a

　　way to reduce the gas pressure at the bottom of Lake Nyos．They stood a 672-foot plastic pipe in

　　the middle of the lake，with one end of the pipe near the bottom and the other end in the air．Near

　　the top of the pipe，the team put several holes that could be opened or closed by a #puter．Now，

　　when the gas pressure gets too high，the holes are opened and some of the gas-filled water shoots

　　up through the pipe into the air like a fountain．With less pressure，a disastrous explosion is much

　　less likely．However, the scientists are not sure that one pipe will be enough to prevent explosions．They hope to put in others soon and they plan to install a similar pipe and a #puter system at Lake Monoun as well． 

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