托福听力背景材料之龙舌兰洞.docx

托福听力背景材料之龙舌兰洞在托福听力讲座中，具有特色的地质现象是非常热门的一个话题。ETS设置这样其的原因可以分为两点：一、美国地大物博，各种有趣的地质现象种类繁多，以此为话题，可以规避一些同学惯于用已有的背景知识去套用新的听力内容。二、各式各样的地质现象通过教授引人入胜的描述显得格外具有吸引力，让学生在考试的时候能够有浓厚的兴趣继续听下去，并且丰富了学生们的地理知识。那么，今天我们就以一篇TPO中出现过的地质学文章来窥探美国地理的一角。Now there are some pretty interesting caves in parts of the western United States, especially in national parks. There is one part that has over a hundred caves, including some of the largest ones in the world. One of the more interesting ones is called Lechuguilla Cave. Lechuguilla has been explored a lot in recent decades.教授在讲座开始就说到在美国国家地质公园里有许多有趣的洞穴，其中就有一些世界上最长的洞。教授今天要讲的是一个叫做龙舌兰洞的地方。那么，这个洞有什么特别之处呢?Its one of the longest and deepest limestone caves not just in the country but in the world.龙舌兰洞是世界上最长最深的石灰岩洞。嗯既然是世界之最，的确够impressive! It was formed because of sulfuric acid.它是由硫酸形成的。由硫酸形成的为什么就值得一提呢?There are two kinds of limestone caves. In about 90 percent of them, you have water from the surface, streams, waterfall or whatever - moving water that flows through cracks found in limestone. Its the moving water itself that wears away at the rock and makes passageways. Also, in surface water, there is a weak acid, carbonic acid, not sulfuric acid but carbonic acid that helps dissolve the rock. With a little help from this carbonic acid, moving water forms most of the worlds limestone caves. 原来是因为世界上的石灰岩洞分为两种，一种是由流动的水和水中存在的一丢丢弱酸碳酸形成的，百分之九十的石灰岩洞都是这样形成的;另一种石灰岩洞的形成依赖于一种强酸硫酸，是硫酸腐蚀了石灰岩从而形成通道，而不是水，所以这种洞也被叫做无水洞。既然多数洞穴都是在水的作用下形成的，那么这由硫酸形成的龙舌兰洞自然就显得很特立独行充满个性咯。The formations there, is really something. Theres such variety there like nothing anywhere else in the world, some of them are elaborate looking, like decorations. And a lot of them are made of gypsum and could be up to 20 feet long. Its pretty impressive.这个龙舌兰洞的内部构造又是怎么样的呢?原来硫酸和石灰岩反应会生成一种沉淀叫做石膏，这东西越堆积越高，最后形成了高大的塔状结构，所以是非常壮观的。而且因为石膏是可溶于水的，这也就再次证明了龙舌兰洞是无水洞。问题来了，这个硫酸是哪来的呢?肯定不是谁跟这个洞有仇泼进去的，让我们继续一探究竟吧。Part of the limestone rock layer is permeated by water from below. Those curly lines are supposed to be cracks in the rock. Below the water table and rock is oil. Bacteria feed on this oil and release hydrogen sulfide gas. This gas is hydrogen sulfide, rises up and mixes with oxygen in the underground water that sits in the cracks and fissures in the limestone. And when hydrogen sulfide reacts with the oxygen in the water, the result of that is sulfuric acid, Ok? Sulfuric acid eats away at limestone very aggressively. So you get bigger cracks and then passageway is being formed along the openings in the rock and its all underground. 就是说，部分的石灰岩是浸没在地下水中的，而且这些石灰岩上是有裂缝的，所以肯定就会有水在这些缝隙里，对吧?在岩层和水层的下面就是地下油层，这油层里有细菌，细菌以这些油为食释放出一种叫做硫化氢(hydrogen sulfide, H2S)的气体,硫化氢气体上升到岩石留缝中的水并和水里的氧气结合就生成了硫酸，硫酸腐蚀石灰岩，使得裂缝变成通道。了解了龙舌兰洞的形成，我们还有一个关心的问题就是，这个洞现在是活的还是死的呢?Lechuguilla is pretty much dormant now. Its not really forming any more. But, there is other ones like it, for example, in Mexico, that are forming. And when cave researchers go to explore them, they see and smell, the sulfuric acid and gases of.er.phew.now, something else, think of rotten eggs. And, its not just the smell. Explorers even need to wear special masks to protect themselves from the gases in these caves.答案是：它已经休眠了。因为我们刚才说到在形成的过程中有一种气体叫做硫化氢气体，大家都知道这货是个有臭鸡蛋气味的有毒气体。其他的无水洞因为还在形成，探险家们为了不让自己被这味道熏到，都要佩戴特制的面具来保护自己。看，这是不是很