The Exploding Lakesof Cameroon

What comes to mindwhen you think of a lake?You probably imagine a pretty scene with bluewater,birds,and fish.For the people in the northwestern Cameroon,however,the

image is verydifferent. For them,lakes may mean terrible disasters.In 1984,poisonous gasesexploded out of Lake Monoun and came down intothe nearby villages,killing

thirty-sevenpeople.Two years later,Lake Nyos erupted.A cloud ofgases rolled down the hills and into the valleys and killed 1,700 people.

Lake Nyos and LakeMonoun are crater（火山口）lakes.They were formed when water collected in the craters of old volcanoes.Thevolcanoes under Lake Nyos and Lake

Monoun are notactive anymore.However,poisonous gases from the center of the earth continue toflow up through cracks in the bottom of the lake.This is normal in a crater

lake.In most craterlakes,these gases are released often because the water"turnsover"regularly.That is,the water from the bottom of the lake rises andmixes with the water at

the top,allowing thegases to escape slowly.

However,in Lakes Nyosand Monoun,there is no regular turning over. No one knows the reason for thisfact,but as a result,these lakes have more gases trapped at the bottom

than other craterlakes.In fact,scientists who have studied Lakes Nyosand Monoun have found 16,000 times more gases. When a strong wind , coolweather, a storm, or a

landslide（滑坡）causes the water to turn oversuddenly,the gases escape in a violent explosion.

In the past,no oneknew when the gases might explode,so there was no way for the villagers toescape disaster. Now scientists from the United States,France,andCameroon

have found a way toreduce the gas pressure at the bottom of Lake Nyos.Theystood a 672-foot plastic pipe in the middle of the lake,with one end of thepipe near the bottom

and the other end inthe air. Near the top of the pipe,the team put several holes that could beopened or closed by a computer. Now,when the gas pressure gets too high,the

holes are opened andsome of the gas-filled water shoots up through the nine into the air like afountain.With less pressure,a disastrous explosion is much less

likely.However,thescientists are not sure that one pipe will be enough to prevent explosions.Theyhope to put in others soon and they plan to install a similar pipe and a

computer system at Lake Monounas well.

To protect peoplenearby until all of the pipes are in place,the scientists have installed earlywarning systems at both lakes.If the gas pressure rises to a dangerous

level,computers willset off loud sirens（警报）andbright lights to warn the people in the villages. In that way,they will havetime to escape from the dangerous gases.What do we learnfrom the last paragraph?

A.Scientists areplanning to install pipes in all crater lakes.

B.Scientists stilldo not know how to prevent gas explosions.

C.Explosiondisasters could be avoided in the future.

D.Warning systemshave been set up in the villages nearby.