『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 48 Lec 2听力练习：What is the lecture mainly about?原文题目答案解析，TPO/Official 48 Lec 2听力原文范文音频翻译。

托福TPO/Official 48 Lec 2听力原文What is the lecture mainly about?【新东方在线】

旁白：听地球科学课的部分讲座。

Narrator: Listen to part of a lecture in an Earth Science class.

教授：好的。我们知道地球的表面，地壳，是由构造板块组成的，这些巨大的岩石地壳块正在缓慢地在彼此之上或之下滑过或者擦肩而过，

Professor: Okay. We know the Earth's surface, the crust, is made up of tectonic plates, and these huge slabs of rocky crust are slowly sliding over or under or past each other,

我们说世界上大多数火山发生在这些构造板块的边界在那里有热的熔融岩石从板块之间的缝隙挤压而出。

and we said that most of the world's volcanoes occur at the boundaries of these tectonic plates where you have hot molten rock squeezing up through gaps between the plates.

但一些火山不出现在边缘，而是在大陆或海洋板的中间。

But some volcanoes occur not at the edges, but in the middle of a continental or oceanic plate.

例如，夏威夷群岛，距离任何板块边界都有数千公里的距离，但有大量的岩浆，

The Hawaiian Islands, for example, are thousands of kilometers away from any plate boundary, and yet you have vast amounts of magma,

熔融岩石岩或熔岩向上流过地壳，这意味着，当然，火山活动不可以简单地通过板块构造解释。

molten rock or lava, flowing up through the earth's crust, which means, of course, that volcanic activity there can't be explained simply by plate tectonics.

那么，我们如何解释这些火山异常，这些超过一般规则的例外？

So, how do we explain these volcanic anomalies, these exceptions to the general rule?

好吧，早在1963年，一个名叫威尔逊的地球物理学家提出了一个热点理论来解释这种特殊类型的火山活动如何发生，

Well, back in 1963, a geophysicist by the name of Wilson came up with a hot-spot theory to explain how this particular type of volcanic activity can occur,

并可以持续发生几十甚至几亿年。

and can go on for maybe tens or even hundreds of millions of years.

威尔逊的理论是：热点存在于构造板之下，它们是引起这些火山的原因。但是什么原因导致热点？

Wilson's theory was that: hot spots exist below tectonic plates, and they're the cause of these volcanoes. But what causes the hot spots?

嗯，好吧，提出的最流行的理论是地幔柱假说。根据这个假设，地幔柱，

Hmm, well, the most popular theory that's been proposed is the plume hypothesis. According to this hypothesis, plumes,

uh, basically columns of extremely hot magma.

这些岩浆柱从地球内部的深处开始，甚至可以像地心一样深，并且一直上升融化直到地球的地壳。

These plumes well up from deep inside the planet's interior, maybe even as deep as its core, and rise all the way up to melt through the Earth's crust.

想象一个燃烧的蜡烛，想象一张很厚的纸慢慢地移动到蜡烛的火焰上。

Imagine a burning candle, and imagine moving a sheet of heavy paper slowly over the flame of the candle.

你会在纸上得到一系列烧焦的斑点，好吧，就像夏威夷群岛发生的一样，

You're gonna get a series of burned spots in the paper. Well, that's just like what's happening with the Hawaiian Islands,

但是没有纸，现在有一块构造板，它正在这束强烈的热岩浆上方移动，

but instead of a sheet of paper, you've got a tectonic plate, and it's moving over this plume of intensely hot magma,

and rather than a series of burned spots in the paper.

你得到一连串的火山岛，在那里，岩石柱融穿了太平洋下的地壳，一个点连接着一个点，而处于岩浆柱上方的新生的岛屿上形成活火山，而其它岛屿，

You're getting a chain of volcanic islands where the hot plume melts through the crust under the Pacific Ocean at one point after another with active volcanoes on the younger islands that are now just above the plume, and the other islands,

它们离岩浆柱越远，历史越悠久，并且在更早之前，它们的火山进入休眠期或彻底熄灭。

well, the farther away from the plume they are now, the older they are, and the longer ago their volcanoes went dormant or extinct.

顺便说一句，火山岛似乎很小，但被称为大岛夏威夷的岛是地球上最高的地形特征之一，

Incidentally, volcanic islands may seem small, but the island known as the Big Island Hawaii is one of the tallest topographic features on the planet,

从海底到海洋表面超过五公里，几乎同样的高度，直到它的最高峰。

more than five kilometers from the sea floor to the ocean surface, and almost that much again, up to its highest peak.

是从海底到岛上的最高点几乎有十公里，这使得它甚至比珠穆朗玛峰还高。

That's nearly ten kilometers from ocean floor to the highest point on the island, which makes it taller even than Mount Everest.

所以，你可以想象大量的岩浆或熔岩，它们喷涌而出形成一个小岛，何况整个岛屿链。

So, you can imagine the huge amounts of magma, or lava, that've flowed up to form even just this one island, much less the whole chain of islands.

现在，岩浆柱假说为火山异常提供了一个相当简明的解释，如夏威夷群岛。

Now, the Plume Hypothesis provides a pretty elegant explanation for a volcanic anomaly, like the Hawaiian Islands.

但是，虽然它的假设是有吸引力的，但是没有什么直接证据支持这个理论，

But, while it's hypothetically attractive, there's very little direct evidence to support the theory,

因为到目前为止，没有人能够实际观察到地球下方发生了什么。

because so far, no one's been able to actually observe what's happening that far beneath the Earth's crust.

一些研究已经完成，测震学，地球化学，其中数据与模型一致，但它们不是确凿的证据。

Some studies have been done, seismographic, geochemical, where the data's consistent with the model, but they aren't definitive proof.

即使是模型的支持者也不愿意声称这个理论可以解释每一种火山的异常现象。

Even the model supporters are uncomfortable claiming that it explains every volcanic anomaly.

就像任何流行的理论，我想，它有一些确定的批评。

And like any popular theory, I suppose, it has some determined critics.

这些批评者提出了一些备选理论，迄今为止还没有证明。

These critics have put forth a number of alternative theories, all unproven so far.

但一个被广泛认可的理论是裂缝假说，假设当一块地壳被拉伸得越来越薄时产生热点，并且所产生的应力导致在地壳中的薄弱点处产生小裂缝，

But one well-regarded theory is the crack hypothesis, which assumes that hot spots are created when a piece of the crust gets stretched thinner and thinner and the resulting stress causes small cracks,

并且通过这些裂缝岩浆形成火山的裂缝。

to open up at weak spots in the crust, and it's through these cracks that magma pushes up to form volcanoes.

裂隙假设的支持者认为这是一个广泛的现象，并认为岩浆不是从地球内部的深处，

Proponents of the crack hypothesis consider this a widespread phenomenon and believe that magma's not coming up from deep within the Earth's interior,

but rather from just beneath the surface crust.

这个假设是有吸引力的，因为它适用于我们已经知道的板块构造，它也适用于我们所知道的一些次要的较小热点，

This hypothesis is attractive, because it fits with what we already know about plate tectonics and it fits what we know about some secondary smaller hot spots,

但它可以很好的解释夏威夷群岛吗？

but how well does it explain the Hawaiian Islands?

一系列的随机裂纹是否会产生同样特殊的岛屿，这些岛屿的序列也是从老旧到年轻？

Could a series of random cracks produce that same particular string of Islands that's sequenced so neatly from old to young?

你知道，当一个理论依赖于巧合来得出结论时，这理论让我担心。

You know, it worries me when a theory depends on coincidence to produce results.

According to the professor, why was the hot spot theory originally proposed?

Why does the professor describe moving a sheet of heavy paper over a candle?

Why does the professor discuss how high one of the Hawaiian Islands rises above the ocean floor?

According to the crack hypothesis, what causes a hot spot?

What is the professor's opinion of the two main hypotheses he presents?

OK, we know the earth surface, the crusts, is made up of tectonic plates and that these huge slabs of rocky crust are slowly sliding over or under or pass each other. And we said that most of the world’s volcanoes occur at the boundaries of these tectonic plates, where you have hot molten rock squeezing up gaps between the plates. But some volcanoes occur not at the edges but in the middle of a continental or oceanic plate. The Hawaiian Islands, for example, are thousands of kilometers away from any plate boundaries and yet you have vast amounts of magma, molten rock or lava, flowing up through the Earth's crust, which means, of course the volcanic activity there can't be explained simply by plate tectonics. 
So how do we explain these volcanic anomalies, these exceptions to the general rule. Well, back in 1963, a geophysicist, by the name of Wilson, came up with a hotspot theory to explain how this particular type of volcanic activity can occur, and can go on for maybe tens or even hundreds of millions of years. Wilson’s theory was that hotspots exist below tectonic plates, and there the cause of these volcanoes. 
But what causes the hotspots? What the most popular theory has been proposed is the plume hypothesis. According to this hypothesis, plumes are basically columns of extremely hot magma. These plumes well up from deep inside the planet’s interior, maybe even as deep as its core, and rise all the way up to melt through the Earth's crust. Imagine a burning candle and imagine moving a sheet of heavy paper slowly over the flame of the candle, you're gonna get series of burn spots in the paper. Well that's just like what's happening with the Hawaiian Islands, but instead of a sheet of paper, you've got a tectonic plate and it's moving over this plume of intensely hot magma, and rather than a series of burn spots in the paper. And you're getting a chain of volcanic islands with the hot plume melt through the crusts under the Pacific Ocean at one point after another with active volcanoes on the younger islands that are not just bump the plume. And the other islands, well they are farther away from the plume they are now, the older they are and the longer go their volcanoes went through???extinct. Incidentally, volcanic islands may seem small, but the islands known as the big Island of Hawaii is one of the tallest topographic features on the planet, more than 5 km from the Sea floor to the ocean surface. And almost that much again, upped with highest peak. That's nearly 10 km from the ocean floor to the highest point on the island, which makes it taller even then Mount Everest. So you can imagine the huge amounts of magma or lava that have flowed up the form even just this one island much less the whole chain of islands. 
Now the plume hypothesis provides a pretty elegant explanation for a volcanic anomaly like the Hawaiian Islands. But while it's hypothetically attractive, there's very little direct evidence to support the theory, because so far no one’s been able to actually observe what's happening that far beneath the earth’s crust. Some studies have been done, seismographic, geochemical with the data’s consistent with the model that they are definitive proof. Even the model supporters are in comfortable claiming that it explains every volcanic anomaly. And like any popular theory I suppose, it has some determined critics. These critics have put forth a number of alternatives theories, all unproven so far. But one well-regarded theory is the crack hypothesis, which assumes that hotspots are created when a piece of the crust get stretched thinner and thinner, and the resulting stress causes small cracks to open up the weak spots in the crust and it's through these cracks that magma pushes up the form volcanoes. Proponents of the crack hypothesis consider this a widespread phenomenon, and believe that magma’s not coming up from deep within the Earth's interior, but rather from just beneath the surface crust. This hypothesis is attractive because it fits with what we already know about plate tectonics, and it fits what we know about some secondary smaller hotspots. But how well does it explain the Hawaiian Islands? Could a series of random cracks produce that same particular string of islands that sequence so neatly from old to young? You know, it worries me when a theory depends on coincidence to produce results.

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