<-NARRATOR:->Listen to part of the lecture in an Earth Science class. The class has been discussing volcanoes.

旁白：请听地球科学课上的部分内容。这节课讨论的是火山。

<-MALE 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.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.

教授：我们知道地球的表面也就是地壳是由地壳板块构成的，这些巨大的岩壳慢慢地滑到彼此上方或下方，或滑过对方。我们说世界上大部分的火山都是在这些地壳板块的交界处喷发的，在这些地方熔化了的炙热岩石通过这些板块之间的裂缝不断挤压上涌。

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 boundary.And yet you have vast amounts of magma, 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.

但是有一些火山不在边缘处喷发，而是在一个大洲或海洋板块的中央喷发举个例子来说，夏威夷群岛，距离任一板块界线都有数千公里远。但却有巨大数量的岩浆穿过地壳喷涌而出，这无疑意味着那里的火山活动不能简单地用板块构造论来解释。

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

那么，我们该如何解释这些异常的火山，这些一般规则的例外呢？

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, and can go on for maybe tens or even hundreds of millions of years.Wilson's theory was that: hot spots exist below tectonic plates, and they're the cause of these volcanoes.

在1963年，一位叫做Wilson的地球物理学家提出了一个热点理论来解释这种类型的火山活动是如何发生，并持续数千万年甚至数亿年的。Wilson的理论是：地壳板块下存在着热点，而它们正是这些火山产生的原因。

But what causes the hot spots?

但是什么导致了这些热点的出现呢？

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

已提出的理论中支持率最高的是地幔柱理论（Plume Hypothesis）。

According to this hypothesis, plumes, uh, 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.

根据这个理论，地幔柱......基本上就是极其炙热的岩浆柱形物。 这些地幔柱从地球内部的深层区域涌出，也许甚至有地核那么深，然后一路上涌熔化地壳。

Imagine a burning candle, and imagine moving a sheet of heavy paper slowly over the flame of the candle.You're gonna get a series of burned 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 burned spots in the paper, 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’re now just above the plume, and the other islands … well, the farther away from the plume they are now, the older they are and the longer ago their volcanoes went dormant or extinct.

想象一下一根燃烧着的蜡烛，再想象一下慢慢把一张很厚的纸移到蜡烛火焰的上方，你会看到纸上有一连串烧焦了的斑点。这和夏威夷群岛正在发生的事情是一样的，而那不是一张纸，只不过那是一个地壳板块，它正移动到这种炙热的岩浆火焰上方。与纸上一连串烧焦的斑点不同，出现的是一连串的火山岛，在这里炙热的地幔柱一个点接一个点地熔化了太平洋海底的地壳，而现在正处于岩浆火焰上方的形成时间较短的海岛上有着活跃的火山。而其他岛屿，它们现在离地幔柱越远，形成的时间就越长，它们的火山沉寂或熄灭的时间就越早。

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, more than five kilometers from the sea floor to the ocean surface, and almost that much again, up to its highest peak.That's nearly ten kilometers from ocean floor to the highest point on the island, which makes it taller even than Mount Everest.

偶尔火山岛看上去也许很小，但是像夏威夷这样知名的大岛是地球上最高的地形特征之一，从海床到海平面超过5千米，从海平面到其顶峰差不多也有那么高。从海床到这座岛的最高点将近有一万米，这使得它甚至比珠穆朗玛峰（喜马拉雅山主峰之一）还要高。

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.

所以不难想象出喷涌而出形成这一座岛的岩浆数量之巨大，更不用说这整个群岛。

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.

地幔柱理论为像夏威夷群岛这样的异常火山提供了一个非常得体的解释。但是，虽然这个理论很有吸引力，但是几乎没有直接证据能够支持这一理论，因为到目前为止，没人能够真正观察到那么深层的地壳在发生什么。

Some studies have been done, seismographic, geochemical, where the data's consistent with the model, but they aren't definitive proof.Even the model supporters are uncomfortable claiming that it explains every volcanic anomaly, and like any popular theory, I suppose, it has some determined critics.

人们进行了一些地震学、地球化学方面的研究，这些研究中得出的数据和模型是一致的，但是它们不是最可靠的证据。虽然这个模型的支持者们都不愿宣称这个理论能解释所有异常的火山， 像所有的流行理论一样，我认为它也有一些很坚决的批评家。

These critics have put forth a number of alternative theories, all unproven so far.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 to open up at weak spots in the crust, and it's through these cracks that magma pushes up to form volcanoes.

这些批评家提出了大量的可替代理论，所有的这些理论目前都未得到证明。不过有一个很值得考虑的理论，那就是裂缝理论，这一理论认为当一块地壳被拉伸得越来越薄时就产生了热点，同时产生的压力导致小裂缝，在地壳不牢固的地点打开， 而岩浆正是通过这些裂缝上涌形成火山的。

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.

裂缝理论的支持者们认为这是一个广泛分布的现象，并相信岩浆只是从表面的地壳下喷涌而出的，而不是从深层的地球内部出来的。

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, but how well does it explain the Hawaiian Islands?Could a series of random cracks produce that same particular string of Islands that's sequenced so neatly from old to young?You know, it worries me when a theory depends on coincidence to produce results.

这个理论很有吸引力，因为它符合我们已知的关于板块构造论的知识，而且符合我们对一些次要的更小的热点的了解，但是它在解释夏威夷群岛方面表现如何呢？一系列杂乱的裂缝能产生同样特殊的按照形成时间长短排列得如此有序的岛屿群吗？当一个理论要依靠巧合才能得出结果时，真的令我忧心忡忡。