環(huán)球英語 — 584：The Language of Volcanoes
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Hello. I’m Ruby Jones
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And I’m Marina Santee. Welcome to Spotlight. This programme uses a special English method of broadcasting. It is easier for people to understand, no matter where in the world they live.
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‘Suddenly you know that the volcano is speaking to you. And you understand the language. This is a defining moment.’
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Scientist Bernard Chouet said these words. He was talking about an important time in his work. It was when he discovered a secret that would save thousands of lives. For years, scientists had wanted to know how to predict the time a volcano would erupt. If they could warn people that a volcanic mountain would soon explode, people living near it could escape.
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In today’s programme we look at the work of a man called Bernard Chouet - and how he has shaped the course of volcano science.
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A volcano is an amazing sight, but also very frightening - a huge mountain with a mouth that blows out hot melted rock and gases. Volcanoes permit gases to escape from deep below the earth. And they permit liquid rock, called magma, to escape. The magma moves up and up. If the top of the volcano is closed there is nowhere for the magma to go. The high pressure pushes against the top of the volcano. Finally, it pushes through the top - causing the volcano to explode or erupt.
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In the past, there has been no clear warning as to exactly when a volcano would erupt. This has resulted in many injuries and deaths.
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In 1985 the Nevado del Ruiz Volcano erupted. More than twenty thousand people died. This tragic event deeply troubled scientists. How could they prevent volcanoes from causing such great loss of life? They had to find a way to predict when a volcano would erupt. The answer came through the work of one particular scientist - Bernard Chouet.
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Bernard Chouet was different from other volcanologists. Yes he studied volcanoes, and examined their behaviour. But his earlier training was in other areas of science. This gave Chouet extra skills in understanding one of the key instruments for studying volcanoes - seismographs. Seismographs record earthquakes that happen inside the volcano. These records are called seismograms. The seismograms show the sounds of the rocks breaking. There is only one thing that can break solid rock inside a volcano - liquid rock - magma. As magma moves up the volcano, it breaks through rock. And so seismograms show the travel path of magma. For many years, scientists studied seismograms and eruptions of volcanoes. They looked for a link between the two. However, there did not seem to be a link. Scientists could not see any repeats in the behaviour.
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Bernard Chouet studied the seismograms. He saw the main signal that other scientists had studied. But he was particularly interested in a second layer of information - a weaker signal hidden under the main signal. Scientists knew about it, but they did not know what it meant. However, Chouet’s particular scientific skills caused him to notice something more. He saw the shapes repeating themselves beautifully on the seismogram!! He called these shapes ‘long period events.’
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Chouet explained that the magma moves up the volcano, breaking rock on its way. The hot magma blowing through the broken rock produces a signal that the seismograph can sense. Scientists call this signal “resonance”. Resonance is the same effect that produces sound when a person blows air into a pipe. In the seismogram, the resonance signal shows as the series of long shapes - the ‘long period events.’ Chouet discovered that there are more long period events when the volcano is closer to exploding. So, long period events could show when a volcano would soon erupt.
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However, Chouet was not the only scientist trying to understand volcanoes. Another scientist was working on a completely different method. His name was Stanley Williams. Williams climbed into volcanoes to learn about them! And, he believed the answer was in measuring gases. Magma releases gases into the air above the volcano. The gases are the force behind the eruption. The amount of gas increases as the magma rises under the ground. Williams believed that measuring the gas would help to predict the eruption.
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In 1993, the two ideas came against each other. Some scientists met together at Galeras. Galeras is a volcano in southern Colombia. They planned to go into the volcano to study it. Williams’ gas readings showed that the volcano was safe. But Chouet’s long period events warned that the volcano may erupt. The scientists discussed what to do. Chouet’s methods were not well known. And, Chouet was unable to be at the meeting - to explain more. And so the scientists decided to go ahead and trust the gas method. They went into the volcano.
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On the 14th of January, 1993 Galeras erupted. It killed six of the scientists. Stanley Williams survived. But he suffered permanent injuries.
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On the Galeras trip, Chouet’s methods had proved to be correct. But the cost was high. The tragic event created respect for Chouet’s work. And people began to listen to his theory.
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In December 2000, Mexican scientists used Chouet’s methods. They saw the long period events on the seismograph for the volcano Popocatepetl. The events were greatly increasing. Bernard Chouet said,
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‘This is like a warning song. The volcano is telling you, "OK I am under pressure here. I am going to blow at the top."’
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The experts in Mexico decided to trust the long period event warning. They showed that Popocatepetl volcano would explode on the eighteenth of December. So, the authorities gave the order. Thirty thousand people had to leave their homes - in less than twenty-four hours. And, on the 18th of December 2000 Popocatepetl erupted. It was the largest eruption for a thousand years. But no one was hurt.
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Today, Bernard Chouet’s method is one of several that scientists use to try to predict volcanic eruptions. It is still too early to say if the method will always work. But Chouet has made great progress in understanding the science of volcanoes. He said;
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‘Science works through a painful process of research and testing. You have to show that process works for other volcanoes as well. Because there is so much more richness in nature than anyone can imagine.’
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Bernard Chouet’s work has proven what many scientists already knew. Humans do not have to be powerless victims in natural tragedies. There are warnings and signs in nature. It is just a case of understanding the language.
