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黄石超级火山爆发?也许就在你有生之年

更新时间:2017-10-12 18:45:39 来源:纽约时报中文网 作者:佚名

A Surprise From the Supervolcano Under Yellowstone
黄石超级火山爆发?也许就在你有生之年

Beneath Yellowstone National Park lies a supervolcano, a behemoth far more powerful than your average volcano. It has the ability to expel more than 1,000 cubic kilometers of rock and ash at once — 2,500 times more material than erupted from Mount St. Helens in 1980, which killed 57 people. That could blanket most of the United States in a thick layer of ash and even plunge the Earth into a volcanic winter.

黄石国家公园下面是一座超级火山,一个比普通火山更强大的猛兽。它一次能喷发1000多立方公里的石块和火山灰,比1980年圣海伦山的喷发量高出2500倍,那次喷发导致57人遇难。而这座超级火山如果喷发,可能会把大半个美国裹入厚厚的灰烬,甚至会给地球带来一个“火山之冬”。

Yellowstone’s last supereruption occurred 631,000 years ago. And it’s not the planet’s only buried supervolcano. Scientists suspect that a supereruption scars the planet every 100,000 years, causing many to ask when we can next expect such an explosive planet-changing event.

黄石最后一次爆发是在63.1万年前。而且它还不是地球上唯一一座埋入地下的超级火山。科学家认为,每10万年就会有一次超级火山爆发,给地球留下伤疤,因此有很多人询问我们,下一次出现这样的爆发性巨变会是在什么时候。

To answer that question, scientists are seeking lessons from Yellowstone’s past. And the results have been surprising. They show that the forces that drive these rare and violent events can move much more rapidly than volcanologists previously anticipated.

为了回答这个问题,科学家正在从黄石的历史中寻求信息。结果令人惊讶。它们显示,这些罕见而猛烈事件背后的驱动力量,其变化速度可能比火山学家之前预测的快得多。

The early evidence, presented at a recent volcanology conference, shows that Yellowstone’s most recent supereruption was sparked when new magma moved into the system only decades before the eruption. Previous estimates assumed that the geological process that led to the event took millenniums to occur.

在近期一个火山学会议上提交的早期证据表明,黄石最近的一次超级爆发,是在新的岩浆进入这个系统仅仅数十年后发生的。以前的估计认为,导致那次爆发的地质过程需要数千年的时间来推进。

To reach that conclusion, Hannah Shamloo, a graduate student at Arizona State University, and her colleagues spent weeks at Yellowstone’s Lava Creek Tuff — a fossilized ash deposit from its last supereruption. There, they hauled rocks under the heat of the sun to gather samples, occasionally suspending their work when a bison or a bear roamed nearby.

得出这个结论之前,亚利桑那州立大学(Arizona State University)的研究生汉娜·沙洛(Hannah Shamloo)和同事们在黄石的熔岩溪凝灰岩(Lava Creek Tuff)——最近一次爆发留下的火山灰化石——花费了数周时间。为了收集样本,他们顶着烈日拖运岩石,当野牛或熊偶尔在附近出没时,他们才暂时停下手中的工作。

Ms. Shamloo later analyzed trace crystals in the volcanic leftovers, allowing her to pin down changes before the supervolcano’s eruption. Each crystal once resided within the vast, seething ocean of magma deep underground. As the crystals grew outward, layer upon layer, they recorded changes in temperature, pressure and water content beneath the volcano, much like a set of tree rings.

沙洛后来分析了火山残留物中的晶体痕迹,从中确定了超级火山爆发之前的变化。每个晶体都曾经是地下深处浩瀚沸腾的岩浆海洋的一分子。随着晶体向外逐层增加,它们记录下了火山下的温度、压力和含水量的变化,就像树的年轮一样。

“We expected that there might be processes happening over thousands of years preceding the eruption,” said Christy Till, a geologist at Arizona State, and Ms. Shamloo’s dissertation adviser. Instead, the outer rims of the crystals revealed a clear uptick in temperature and a change in composition that occurred on a rapid time scale. That could mean the supereruption transpired only decades after an injection of fresh magma beneath the volcano.

“我们本来以为这个进程是在爆发前的数千年中推进的。”亚利桑那州立大学的地质学家、沙洛的论文导师克里斯蒂·蒂尔(Christy Till)表示。而实际上,晶体的外边缘显示了温度的明显升高和成分组成变化是在很快的一个时间尺度中出现的。这可能意味着新鲜岩浆进入火山下面的几十年后,火山就出现了超级爆发。

The time scale is the blink of an eye, geologically speaking. It’s even shorter than a previous study that found that another ancient supervolcano beneath California’s Long Valley caldera awoke hundreds of years before its eruption. As such, scientists are just now starting to realize that the conditions that lead to supereruptions might emerge within a human lifetime.

从地质学上说,这个时间尺度就是一眨眼的功夫。以前的研究发现另一座古老的超级火山——位于加利福尼亚长谷火山口下——在苏醒后的数百年之后就爆发了,而本次发现的时间尺度比那更短。因此,科学家们刚刚开始意识到,在一个人的有生之年里,导致超级爆发的条件可能就会出现。

“It’s shocking how little time is required to take a volcanic system from being quiet and sitting there to the edge of an eruption,” said Ms. Shamloo, though she warned that there’s more work to do before scientists can verify a precise time scale.

“一个火山系统从沉寂不动到爆发边缘只需要这么短的时间,非常令人震惊,”沙洛说。但是她也提醒,在科学家们能够确定精确的时间尺度之前,还有更多的工作要做。

Kari Cooper, a geochemist at the University of California, Davis who was not involved in the research, said Ms. Shamloo and Dr. Till’s research offered more insights into the time frames of supereruptions, although she is not yet convinced that scientists can pin down the precise trigger of the last Yellowstone event. Geologists must now figure out what kick-starts the rapid movements leading up to supereruptions.

没有参与这项研究的加州大学戴维斯分校(University of California, Davis)的地球化学家卡里·库珀(Kari Cooper)说,沙洛和蒂尔的研究提供了更多关于超级爆发的时间框架的见解,尽管她还不相信科学家可以确定黄石上次爆发的精确导火索。地质学家现在必须弄清楚,究竟是什么因素导致了超级爆发的快速形成。

“It’s one thing to think about this slow gradual buildup — it’s another thing to think about how you mobilize 1,000 cubic kilometers of magma in a decade,” she said.

“思考缓慢的逐渐积累过程是一回事——思考如何在十年内让1000立方公里的岩浆动起来是另一回事。”她说。

As the research advances, scientists hope they will be able to spot future supereruptions in the making. The odds of Yellowstone, or any other supervolcano, erupting anytime soon are small. But understanding the largest eruptions can only help scientists better understand, and therefore forecast, the entire spectrum of volcanic eruptions — something that Dr. Cooper thinks will be possible in a matter of decades.

随着研究的进行,科学家们希望能够预测出未来的超级爆发。黄石或任何其他超级火山很快爆发的可能性很小。但是弄明白最大规模的爆发,可以帮助科学家更好地了解火山爆发的全部情况——库珀博士认为在几十年内就有可能办到这一点。

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