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銆€銆€The Exploding Lakes of Cameroon

銆€銆€What comes to mind when you think of a lake? You probably imagine a pretty scene with blue water锛宐irds锛宎nd fish.For the people in the northwestern Cameroon锛宧owever, the image is very different. For them锛宭akes may mean terrible disasters. In 1984锛宲oisonous gases exploded out of Lake Monoun and came down into the nearby villages锛宬illing 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.

銆€銆€Lake Nyos and Lake Monoun are crater(鐏北鍙�)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锛宼hese gases are released often because the water'turns over'regularly.That is锛宼he water from the bottom of the lake rises and mixes with the water at the top锛宎llowing the gases to escape slowly.

銆€銆€However锛宨n Lakes Nyos and Monoun锛宼here is no regular turning over.No one knows the reason for this fact锛宐ut as a result锛宼hese lakes have more gases tapped at the bottom than other crater lakes. In fact锛宻cientists who have studied Lakes Nyos and Monoun have found 16,000 times more gases.When a strong wind锛宑ool weather a storm锛宱r a landslide(婊戝潯)causes the water to turn over suddenly锛宼he gases escape in a violent explosion.

銆€銆€In the past锛宯o one knew when the gases might explode锛宻o there was no way for the villagers to escape disaster. Now scientists from the United States锛孎rance锛宎nd 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锛寃ith one end of the pipe near the bottom and the other end in the air.Near the top of the pipe锛宼he team put several holes that could be opened or closed by a computer.Now锛寃hen the gas pressure gets too high锛宼he holes are opened and some of the gas-filled water shoots up through the pipe into the air like a fountain.With less pressure锛宎 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 computer system at Lake Monoun as well.

銆€銆€To protect people nearby until all of the pipes are in place.the scientists have installed early warning systems at both lakes. If the gas pressure rises to a dangerous level锛宑omputers will set off loud sirens(璀﹀牨)and bright lights to warn the people in the villages.That way, they will have time to escape from the dangerous gases.

銆€銆€41 What will happen when Lake Nyos and Lake Monoun explode?

銆€銆€A Water will flow down the hills

銆€銆€B Poisonous gases will be released suddenly.

銆€銆€C A strong wind will rise from the lakes

銆€銆€D The volcanoes will come to life.

銆€銆€42 Which of the following statements about Lake Nyos and Lake Monoun is true?

銆€銆€A They were formed in 1984.

銆€銆€B They are at the top of two active volcanoes.

銆€銆€C They are not like most other crater lakes.

銆€銆€D Water in them turns over regularly.

銆€銆€43 Lake Nyos and Lake Monoun explode because

銆€銆€A the gases rise to the top and mix with air.

銆€銆€B people from the villages turn over the water.

銆€銆€C scientists have put in a computer system.

銆€銆€D they have more gases trapped at the bottom than other crater lakes

銆€銆€44 A team of scientists has

銆€銆€A erected a pressure-releasing pipe in the lake

銆€銆€B identified the gases at the bottom of the lake

銆€銆€C built a beautiful fountain near the lakes

銆€銆€D removed all dangerous gases from the lakes

銆€銆€45 What do we learn from the last paragraph?

銆€銆€A Scientists are planning to install pipes in all crater lakes.

銆€銆€B Scientists still do not know how to prevent gas explosions

銆€銆€C Explosion disasters could be avoided in the future

銆€銆€D Warning systems have been set up in the villages nearby.

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