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Holy crap, holy crap.
我勒个去！不是吧！
In Yosemite Valley, rockfalls like this one can happen every 4-5 days,
在优胜美地峡谷，每隔四五天就会有这种大小的岩石发生崩塌，
where boulders that can be larger than your average car or apartment building thunder down steep mountainsides.
比一般的汽车或公寓楼都大的巨石从陡峭的山坡上轰鸣而下。
Greg Stock is a geomorphologist who works alongside USGS engineer Brian Collins.
格雷格·斯托克是一名地貌学家，他的搭档是美国地质勘探局的工程师布莱恩·柯林斯。
Using a combination of high-res photography, Lidar, aerial surveillance, and 3D modeling, it's their job to monitor rockfalls in the park,
他们的职责是通过结合高分辨率摄影，激光雷达，空中监测和3D建模监控优胜美地国家公园的落石，
which is critical, especially when five million visitors pass through Yosemite each year.
这一工作，尤其是对每年接纳的游客量多达500万的优胜美地国家公园而言，至关重要。
I do think that Yosemite is tailor-made for rockfalls, because the cliffs are gigantic.
我深深地觉得优胜美地是一个专为落石而生的地方，因为这里的峭壁规模实在是太大了。
One example would be a rockfall in 1996 where a big chunk of rock free fell most of the 3,000 feet down to the valley floor,
举例来说，1996年那次岩崩发生时，一块巨大的岩石从3000英尺（900多米）的高空自由落体落到谷底，
and when it hit as an intact block, it generated category five hurricane strength winds and that blew over a thousand trees in a matter of seconds.
当它完整地砸到地面时产生的风力强达五级，顷刻间便吹倒了上千棵树木。
So what happened in those final moments to cause the rock to leave the cliff?
那么，岩石在离开悬崖前的最后时刻究竟发生了怎样的变化呢？
We know that there are probably decades, or even centuries of preparing that rock to fall,
我们都知道，岩石在崩塌前可能需要酝酿几十年甚至几个世纪的时间，
but the trigger would be that last thing.
但真正触发岩崩的是最后那一刻发生的事情。
That's the straw that breaks the camel's back.
那才是压死骆驼的最后一根稻草。
Roots can grow into these cracks and the roots will expand and push the rocks off,
植物的根会从挤入这些裂缝，将岩石挤开，导致其崩落，
when water freezes in the cracks, that can also push them off.
水在岩缝中结冰时也会将岩石挤开。
However, roughly a third of the rockfalls in Yosemite happen at times when Greg and Brian aren't able to identify a trigger.
然而，优胜美地有大约三分之一的岩崩是格雷格和布莱恩无法确定触发因素的。
Historically, rockfalls were only recorded if they had been witnessed by humans.
从历史来看，岩崩只有在人类亲眼目击时才会被记录下来。
So to be able to track and learn from events that may happen when no one is around,
所以，为了追踪、了解没有人在场时可能发生的情况，
Greg and Brian use a host of other tools.
格雷格和布莱恩还用到了许多其他的工具。
One of those tools is ground-based laser scanning, or it's also called terrestrial LiDAR.
其中包括安装在地面的激光扫描仪，又称“地面激光雷达”。
This basically gives us just millions and millions of points that we can create a three-dimensional model of the cliff.
这一设备可以为我们提供无数创建悬崖三维模型所需的数据。
So we use high-resolution photography a lot of times.
我们会反复用到高分辨率摄影机。
You can use these photos to zoom in very carefully on different aspects of the wall,
这样我们就可以从不同的角度去放大照片中悬崖的细节，
for trying to identify what part of the rockfall was active recently.
从而确定最近哪个位置的落实最为活跃。
In addition, Greg and Brian identify hazard areas where rockfalls have happened before.
此外，格雷格和布莱恩还用这一设备确定了之前发生过落石的危险区域。
Based on their computer models, they know that these are areas where another rockfall event is likely to occur.
根据计算机模型，他们了解到这些区域可能还会发生岩崩事件。
Look at that piece!
看那块儿！
This is really neat, the fact that this new boulder from six months ago, Mm-hmm. Right next to this one.
这块的线条非常干脆，这块新的巨石是六个月前落下来的，没错。就落在了它旁边。
It's adjacent to this one, that's probably a thousand years old or more.
就靠近这一块，这块怕是有一千年多年的历史了。
Right. You got the same pattern happening.
差不多。算得上是历史重演了。
The past is the key to the present. Yup.
过去是认识现在的关键。没错。
Though the team can flag unstable areas, it is difficult to predict when a rockfall will happen.
虽然格雷格他们可以确定哪里的岩石不稳定，他们也很难预测那些岩石具体会什么时候崩落。
Varying weather conditions, quakes, and even wildlife can be the difference between a crack remaining stable for a hundred years, and a major rockfall event.
不同的天气条件、地震甚至野生动植物都可能意味着裂缝是在很长一段时间保持稳定还是发生大型岩崩的区别。
We put in specialized gear called crackmeters behind the cracks, and they measured how much the crack would open over the course of a day.
我们在裂缝后面放入了被称之为“裂缝计”的专用齿轮，这些齿轮能够测量裂缝在一天中裂开的程度。
And we tracked this over three and a half years; what we found was that during periods of heating, the crack would move in and out every day.
这块岩石我们已经跟踪了三年半了；我们发现，天气炎热的时候，裂缝每天都会收缩扩张。
Greg and Brian's research confirmed something rock climbers and geologists have hypothesized, but never proved: that rockfalls could be triggered from hot weather.
格雷格和布莱恩的研究证实了攀岩爱好者和地质学家们猜想到了但从未被证实的一点：炎热的天气也可能引发落石。
Even though we've identified heat now as a probable trigger,
尽管现在我们已经将高温确定为可能的触发因素了，
is the most important thing how hot it was that day?
到底是那天到底有多热最重要呢？
Or is it the fact that maybe it was really cold the day before, and then hot that day?
还是前一天十分寒冷而当天很热这一事实最重要呢？
We don't really know that.
这一点我们确实还未弄清。
Despite the unknowns, Greg and Brian's research is highly valued by scientists that study mountains in Switzerland and Brazil.
尽管存在未知之数，格雷格和布莱恩的研究还是受到了研究瑞士和巴西山脉的科学家的高度重视。
That's because the team have a unique opportunity to amass a huge volume of data based on the number of rockfalls in Yosemite.
这是因为格雷格团队有着绝好的机会根据优胜美地的落石数量积累大量的数据。
There are rockfall deposits here in Yosemite that are way bigger than anything that we've seen happen in the last 150 years.
优胜美地这里堆积的落石比我们在过去150年里看到的任何落石都要大得多。
Which means that there's potential for rockfalls to happen in the future that are much, much bigger than what what we have seen historically.
这也意味着未来这里还有可能发生比我们曾经见证过的规模大得多得多的落石事件。
Which is why Greg and Brian's work is so important.
这也是格雷格和布莱恩的工作为什么至关重要的原因。
It's their data that helps to keep millions of Yosemite visitors safe each year.
因为是他们的数据保障了每年前往优胜美地的数百万名游客的安全。
People come here and they look at these cliffs and my sense is that they think that you know, they've looked this way for thousands of years,
我的感觉是，人们来到这里，看到这些悬崖峭壁，他们会觉得这些峭壁千百年来一直是这个模样，
but that's not true at all.
然而事实并非如此。
The cliffs are changing constantly because of rockfalls.
由于岩崩的反复发生，这里的悬崖一直是处于变化之中的。
This episode was presented by the US Air Force.
感谢美国空军对本期《科学探索之旅》的大力支持。
Learn more at airforce.com.
了解更多信息，请登录airforce.com。
For more episodes of Science in the Extremes, check out this one right here.
了解更多有关极端科学的内容，请查看这一期的视频。
Don't forget to subscribe, and come back to Seeker for more episodes.
不要忘记订阅，回来观看更多《科学探索之旅》栏目的内容。
Thanks for watching.
感谢大家的观看。
