托福阅读：Old Faithful

老忠实喷泉是黄石公园里非常著名的景点之一，但它的名字是如何得来的呢?今天的新托福考试阅读练习资料就会给你答案。

In Yellowstone National Park you can visit the geyser Old Faithful.

It’s a spectacular sight, as each four-minute-long eruption sends boiling water over a hundred and fifty feet high. On today’s Moment of Science, we’ll learn how a geyser works.

Geysers spout up where a column of underground water is heated to boiling by “magma,” or molten rock. Like a pan boiling over on your kitchen stove, this boiling pushes the water upward.

Old Faithful got its name because it used to erupt– faithfully–every sixty-five minutes. It’s been more irregular since a 1959 earthquake disrupted its natural, underground plumbing.

If Old Faithful were exactly like a pan on a stove, you’d expect the water to bubble out continually. What makes it alternate between quiet dormancy and exploding action?

This has to do with the way a deep column of water boils. Water’s boiling point is depending on its pressure. At sea level, water boils at 212°F. Deep under Old Faithful, where the molten rock is, the pressure is much greater. Water won’t boil here until it’s over 300°.

What happens is this: The water column gradually heats, but high pressure keeps the deeper parts from boiling. Finally, the column gets hot enough for the top part to boil off. As the top turns to steam, this reduces the pressure on the deeper water–and lowers its boiling point!

Remember, this deep water is already quite hot. Reducing the pressure makes it boil immediately, further reducing pressure for even deeper water. It’s a rapid chain reaction that makes the whole column boil at once, erupting a spout high into the air. After each eruption, the column refills with cool water from an underground source, and the whole cycle begins again.

译文：

在黄石国家公园，你可以参观老忠实喷泉。每四分钟泉里都会喷出高一百五十英尺的沸水，这可真是一幅壮丽的景色。在今天的科学一刻中，我们将要学习喷泉是如何工作的。地下水柱受到沸腾的“岩浆”(即融化了的岩石)加热便会喷出地表，形成喷泉。就像厨房炉子上煮沸的锅，沸腾加热使水上升。

老忠实泉曾经非常守信地每六十五分钟喷发一次，由此而得名。自从1959年地震破坏了它天然的地下管道以后，老忠实泉就变得更加不规律了。

如果老忠实泉就像在炉子上的锅一样，水会持续不停地沸腾外冒。那么，到底是什么让它一会儿静如冬眠的小兽，一会儿又喷薄不止?

这与底层水柱的沸腾方式有关。水的沸点取决于气压。在海平面上，水达到华氏212度就会沸腾。在老忠实泉的深处，熔岩活动的地方，气压要高得多。在这里，水要达到华氏300度才会沸腾。

于是就有了这样的情况，水柱逐渐加热，但是高压使更深层的水无法沸腾。最后，水柱达到足够的热量使顶部的水汽化。当顶部的水变成蒸汽后，就减少了对深层水的压力-并降低其沸点。

需要明确的是，此时底层的水已经很热了。气压的降低让其迅速沸腾，这样以此类推又紧接着降低更深层的水的压力。这是一个让整个水柱立即沸腾的快速连锁反应，水柱喷薄而出。在每次喷发之后，地下的冷水重新填满水柱，沉静喷发的循环又开始啦!

以上就是这篇托福阅读材料，同学们可以积累其中的词汇及优美句式，找到托福阅读段的主题句，了解托福阅读的几个出题点。托福阅读训练是个长期的过程。大家如果每天做几篇阅读，坚持下来，一定会有不小的进步。预祝大家能有一个好的阅读成绩。