美国国家公共电台 NPR--美国宇航局估计汤加火山爆发威力相当于10兆吨TNT炸药

NASA scientists estimate Tonga blast at 10 megatons

NASA researchers have an estimate of the power of a massive volcanic¹ eruption² that took place on Saturday near the island nation of Tonga.

"We come up with a number that's around 10 megatons of TNT equivalent," James Garvin, the chief scientist at NASA's Goddard Space Flight Center, told NPR.

That means the explosive force was more than 500 times as powerful as the nuclear bomb dropped on Hiroshima, Japan, at the end of World War II.

The blast was heard as far away as Alaska and was probably one of the loudest events to occur on Earth in over a century, according to Michael Poland, a geophysicist with the U.S. Geological Survey.

"This might be the loudest eruption since [the eruption of the Indonesian volcano] Krakatau in 1883," Poland says. That massive 19th-century eruption killed thousands and released so much ash that it cast much of the region into darkness.

In the case of this latest event, Garvin says that he believes the worst may be over — at least for now.

"If the past precedent³ for volcanic eruptions⁴ in this kind of setting has any meaning at all," he added, "then we won't have another one of these explosions for a while."

Even three days after the blast, Tonga remains⁵ largely cut off from the world. Undersea communications cables appear to have been cut, and the airport is covered in ash, preventing relief flights from arriving at the capital city of Nuku'alofa.

Reconnaissance flights by the government of New Zealand showed ash had blanketed houses and many other structures. New Zealand's Foreign Ministry⁶ reported that two people had been confirmed killed and that a tsunami⁷ had inundated⁸ the western coast of the main island of Tongatapu, causing major damage. Wire reports cite the government of Tonga claiming one additional death and even more damage on outlying islands, including Mango island, where all homes have been destroyed.

The volcano behind the eruption had been the subject of study by the NASA team in the years running up to this explosive event. The islands that form Tonga lie along a subduction zone where one part of the Earth's crust dips under another, according to Garvin.

"In this particular case, we don't know when, a kind of volcano with a big summit ring of hills and things formed," Garvin says.

In late 2014 and early 2015, along the rim⁹ of that caldera, volcanic activity built a platform that rose up out of the sea, creating a new island. Layers of steam and ash eventually connected the island, known as Hunga Tonga-Hunga Ha'apai, to two much older islands on either side of it.

Hunga Tonga-Hunga Ha'apai was completely destroyed by Saturday's explosion, says Dan Slayback, a research scientist for NASA's Goddard, as well as Science Systems and Applications Inc. Slayback says the blast was so massive it even appears to have taken chunks¹⁰ out of the older islands nearby.

"They weren't ash — they were solid rock, blown to bits," he says. "It was quite amazing to see that happen."

Garvin says the island's formation also probably seeded its destruction. As it rose from the sea, layers of liquid magma filled a network of chambers¹¹ beneath it. He suspects the explosion was triggered by a sudden change in the subterranean¹² plumbing¹³, which caused seawater to flood in.

"When you put a ton of seawater into a cubic kilometer of liquid rock, things are going to get bad fast," he says.

But for all its explosive force, the eruption itself was actually relatively¹⁴ small, according to Poland, of the U.S. Geological Survey. Unlike the 1991 eruption of Mount Pinatubo, which spewed ash and smoke for hours, the events at Hunga Tonga-Hunga Ha'apai lasted less than 60 minutes. He does not expect that the eruption will cause any short-term changes to Earth's climate, the way other large eruptions have in the past.

In fact, Poland says, the real mystery is how such a relatively small eruption could create such a big bang and tsunami.

"It had an outsized impact, well beyond the area that you would have expected if this had been completely above water," he says. "That's the thing that's just a head-scratcher."

Garvin says that scientists want to follow up with additional surveys of the area around the volcano's caldera. Satellite imagery analysis is already underway and may soon be followed with missions by drones. He hopes the volcano will be safe enough for researchers to visit later in the year.

Poland says he believes researchers will learn a lot more in the days and months to come, as they conduct new surveys of the area.

"This is just a horrible event for the Tongans," he says. But "it could be a benchmark, watershed¹⁵ kind of event in volcanology."

1 volcanic   

adj.火山的；象火山的；由火山引起的

参考例句：

• There have been several volcanic eruptions this year.今年火山爆发了好几次。
• Volcanic activity has created thermal springs and boiling mud pools.火山活动产生了温泉和沸腾的泥浆池。

2 eruption   

n.火山爆发；（战争等）爆发；（疾病等）发作

参考例句：

• The temple was destroyed in the violent eruption of 1470 BC.庙宇在公元前1470年猛烈的火山爆发中摧毁了。
• The eruption of a volcano is spontaneous.火山的爆发是自发的。

3 precedent   

n.先例，前例；惯例；adj.在前的，在先的

参考例句：

• Is there a precedent for what you want me to do?你要我做的事有前例可援吗？
• This is a wonderful achievement without precedent in Chinese history.这是中国历史上亘古未有的奇绩。

4 eruptions   

n.喷发，爆发( eruption的名词复数 )

参考例句：

• There have been several volcanic eruptions this year. 今年火山爆发了好几次。 来自《简明英汉词典》
• Over 200 people have been killed by volcanic eruptions. 火山喷发已导致200多人丧生。 来自辞典例句

5 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

6 ministry   

n.(政府的)部；牧师

参考例句：

• They sent a deputation to the ministry to complain.他们派了一个代表团到部里投诉。
• We probed the Air Ministry statements.我们调查了空军部的记录。

7 tsunami   

n.海啸

参考例句：

• Powerful quake sparks tsunami warning in Japan.大地震触发了日本的海啸预警。
• Coastlines all around the Indian Ocean inundated by a huge tsunami.大海啸把印度洋沿岸地区都淹没了。

8 inundated   

v.淹没( inundate的过去式和过去分词 )；（洪水般地）涌来；充满；给予或交予（太多事物）使难以应付

参考例句：

• We have been inundated with offers of help. 主动援助多得使我们应接不暇。
• We have been inundated with every bit of information imaginable. 凡是想得到的各种各样的信息潮水般地向我们涌来。 来自《简明英汉词典》

9 rim   

n.(圆物的)边，轮缘；边界

参考例句：

• The water was even with the rim of the basin.盆里的水与盆边平齐了。
• She looked at him over the rim of her glass.她的目光越过玻璃杯的边沿看着他。

10 chunks   

厚厚的一块( chunk的名词复数 )； （某物）相当大的数量或部分

参考例句：

• a tin of pineapple chunks 一罐菠萝块
• Those chunks of meat are rather large—could you chop them up a bIt'smaller? 这些肉块相当大，还能再切小一点吗？

11 chambers   

n.房间( chamber的名词复数 )；（议会的）议院；卧室；会议厅

参考例句：

• The body will be removed into one of the cold storage chambers. 尸体将被移到一个冷冻间里。 来自《简明英汉词典》
• Mr Chambers's readable book concentrates on the middle passage: the time Ransome spent in Russia. Chambers先生的这本值得一看的书重点在中间：Ransome在俄国的那几年。 来自互联网

12 subterranean   

adj.地下的，地表下的

参考例句：

• London has 9 miles of such subterranean passages.伦敦像这样的地下通道有9英里长。
• We wandered through subterranean passages.我们漫游地下通道。

13 plumbing   

n.水管装置；水暖工的工作；管道工程v.用铅锤测量（plumb的现在分词）；探究

参考例句：

• She spent her life plumbing the mysteries of the human psyche. 她毕生探索人类心灵的奥秘。
• They're going to have to put in new plumbing. 他们将需要安装新的水管。 来自《简明英汉词典》

14 relatively   

adv.比较...地，相对地

参考例句：

• The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
• The operation was relatively painless.手术相对来说不痛。

15 watershed   

n.转折点，分水岭，分界线

参考例句：

• Our marriage was at a watershed.我们的婚姻到了一个转折关头。
• It forms the watershed between the two rivers.它成了两条河流的分水岭。