The Exploding Lakesof Cameroon

What comes to mindwhen 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 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.Theywere formed when water collected in the craters of old volcanoes.The volcanoesunder Lake Nyos and Lake

Monoun are notactive anymore.However, poisonous gases from the center of the earth continueto flow 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"turns over"regularly.That is,the water from the bottom of the lake rises and mixes withthe 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 Nyos and Monoun have found16,000 times more gases.When a strong wind,cool weather,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 pipe 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.