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参考译文: Heat ID'd as Subtle Cause of Rockfalls 温度上升岩石下落 The floor of Yosemite Valley is littered with piles of rocks that crumbled off the park's iconic cliffs.

These rockfalls happen all the time, becauseYosemite's granite walls are riddled with cracks produced by geologic stress. Scientists know the rockfalls can be triggered by things like earthquakes, rainfall, and freezing and thawing ice. But many falls occur without an obvious cause. Now researchers think that heat may be the culprit. Yosemite Valley山谷的地面散落着成堆的从公园内特有的悬崖峭壁上崩裂下的岩石.这些散落岩石之事时有发生,因为Yosemite山谷上的花岗岩峭壁因为地质上的压力造成了许多断裂的空洞.科学家们知道这些岩石散落的原因可以是地震,暴雨以及冻融的冰河.但是,多数情况下岩石坠落的毫无征兆.现在研究人员认为热能也许是罪魁祸首. "We noticed that there had been a bunch of rockfalls that were happening in the summertime, on particularly hot days." Brian Collins, a research civil engineer with the U.S. Geological Survey. "And we noticed when we looked at the timing that they were happening in the afternoon, when we thought the temperatures were at their hottest." 我们已注意到,当在夏季的时候,会有许多的岩石坠落,特别是很热的那几天.这是Brian Collins,美参与国地理调查的城市工程研究人员.我们还注意到,发生岩石坠落的事件往往是下午,我们过去认为此时是一天中最热的一段时间. Collins and Greg Stock, Yosemite's park geologist, wanted to know if small rock movements, induced by changing temperatures, might weaken cracks and contribute to rock falls. So the researchers―who are both climbers―found a suitable fracture near the base of a 500-meter-tall cliff and installed instruments called crack meters, which monitored the width of the crack over time. Collins 和Greg Stock, Yosemite公园中的地理学家,他们希望知道是否由于温度的变化引发的小型岩石移动事件,会使山体的裂缝变得脆弱,从而最后导致岩石坠落.所以这些研究人员们――他们还都是登山爱好者――在接近500米高的山崖底部发现了的 一块小片地区,并且安装了被称为裂缝仪的设备,用于检测不同时间下岩石裂缝的宽度. The devices revealed that the crack grew almost a centimeter wider during the warmest part of the day. It shrank again when temperatures cooled off, for instance, at night and during the winter. But overall, the scientists found that the average width of the fracture grew over the course of a summer and over the entire three and a half-year study period, bringing the crack closer to breaking. 应用这些设备显示出,裂缝在一天中最温暖的时段里几乎被拓宽了一厘米.当温度再次变低后它又收缩回去了,比如,在晚间和冬季时段.但是,总体上讲,科学家们发现断裂处的平均宽度是在整个夏季是增加的,并且在他们整个3.5年的研究期间也是增加的,这些都造成了裂缝增加岩石趋于断裂. "We think that what happened was that every cycle ― as the rock goes back and forth and back and forth ― you're getting to a part that we call subcritical crack growth. And that means that the crack where the rock is attached to the cliff is actually fracturing at a microscopic level. And so if you do that over the course of a year, then eventually you're going to do some permanent damage to those points of attachment." The study is in the journal Nature Geoscience. 我们认为发生了循环――随着岩石来来回回滚动――你正处一个我们称之为临界裂缝增长的阶段.这就意味着,岩石连接着山崖的裂缝部分实际上正在以微小的幅度断裂着.所以,如果你在一年中的这个阶段这么做,那么最后,你就在对那些连接点进行永久性的破坏.该研究结果已经发表在《自然地理科学》杂志上. The slab of rock the scientists studied hasn't fallen yet, and Collins doesn't know how many cycles it will take before this or any other fracture finally breaks. When it does, the trigger might be a particularly sweltering day, when the partially detached slab is farthest away from the cliff. Or it could be another process, helped along by the fact that temperature changes already weakened the crack. 科学家们研究的岩石板还没有坠落,而Collins也不知道在这个或者其它最后要断裂的部分会在多少个上述微小的循环刺激之下才会最终断裂.一定在是某个特别闷热的日子,当特别的一块岩石板从山崖上飞速脱离时,岩石就发生断裂了.或者,由于另外的事件,由于温度变化帮助了已经很脆弱的岩石裂缝,造成最后的断裂. Either way, the results will help researchers assess the rockfall hazard in steep, rugged terrain. Because now they know when the mercury goes up, rocks are more likely to come down. 无论哪种方法,结果都将有助于研究人员们评估陡峭崎岖的岩层地带岩石坠落的灾害风险.因为现在,他们已经知道当水银柱越上升,岩石就越容易坠落. 听力原文: Heat ID'd as Subtle Cause of Rockfalls The floor of Yosemite Valley is littered with piles of rocks that crumbled off the park's iconic cliffs. These rockfalls happen all the time, becauseYosemite's granite walls are riddled with cracks produced by geologic stress. Scientists know the rockfalls can be triggered by things like earthquakes, rainfall, and freezing and thawing ice. But many falls occur without an obvious cause. Now researchers think that heat may be the culprit. "We noticed that there had been a bunch of rockfalls that were happening in the summertime, on particularly hot days." Brian Collins, a research civil engineer with the U.S. Geological Survey. "And we noticed when we looked at the timing that they were happening in the afternoon, when we thought the temperatures were at their hottest." Collins and Greg Stock, Yosemite's park geologist, wanted to know if small rock movements, induced by changing temperatures, might weaken cracks and contribute to rockfalls. So the researchers―who are both climbers―found a suitable fracture near the base of a 500-meter-tall cliff and installed instruments called crackmeters, which monitored the width of the crack over time. The devices revealed that the crack grew almost a centimeter wider during the warmest part of the day. It shrank again when temperatures cooled off, for instance, at night and during the winter. But overall, the scientists found that the average width of the fracture grew over the course of a summer and over the entire three and a half-year study period, bringing the crack closer to breaking. "We think that what happened was that every cycle ― as the rock goes back and forth and back and forth ― you're getting to a part that we call subcritical crack growth. And that means that the crack where the rock is attached to the cliff is actually fracturing at a microscopic level. And so if you do that over the course of a year, then eventually you're going to do some permanent damage to those points of attachment." The study is in the journal Nature Geoscience. The slab of rock the scientists studied hasn't fallen yet, and Collins doesn't know how many cycles it will take before this or any other fracture finally breaks. When it does, the trigger might be a particularly sweltering day, when the partially detached slab is farthest away from the cliff. Or it could be another process, helped along by the fact that temperature changes already weakened the crack. Either way, the results will help researchers assess the rockfall hazard in steep, rugged terrain. Because now they know when the mercury goes up, rocks are more likely to come down.