The ash fall from the last Yellowstone eruption covered all or parts of nineteen western states (plus parts of Canada and Mexico)—nearly the whole of the United States west of the Mississippi. This, bear in mind, is the breadbasket of America, an area that produces roughly half the world's cereals. And ash, it is worth remembering, is not like a big snowfall that will melt in the spring. If you wanted to grow crops again, you would have to find some place to put all the ash. It took thousands of workers eight months to clear 1.8 billion tons of debris from the sixteen acres of the World Trade Center site in New York. Imagine what it would take to clear Kansas.
上一次黄石火山爆发所喷出的火山灰，铺满了西部19个州的全部地区或部分地区（加上加拿大和墨西哥的部分地区）——几乎涵盖了美国密西西比河以西的整个地区。记住，这里是美国的粮仓，生产世界上差不多一半的谷物。还不要忘记，火山灰不像一场大雪那样一到春天就会融化。要想再种庄稼，你不得不找个地方堆放所有的火山灰。几千名工人花了8个月的时间才从纽约世贸中心6.5公顷的废墟上清理掉18万吨垃圾。想一想，清理堪萨斯州要花多少时间。

And that's not even to consider the climatic consequences. The last supervolcano eruption on Earth was at Toba, in northern Sumatra, seventy-four thousand years ago. No one knows quite how big it was other than that it was a whopper. Greenland ice cores show that the Toba blast was followed by at least six years of "volcanic winter" and goodness knows how many poor growing seasons after that. The event, it is thought, may have carried humans right to the brink of extinction, reducing the global population to no more than a few thousand individuals. That means that all modern humans arose from a very small population base, which would explain our lack of genetic diversity. At all events, there is some evidence to suggest that for the next twenty thousand years the total number of people on Earth was never more than a few thousand at any time. That is, needless to say, a long time to recover from a single volcanic blast.
我们还没有考虑对气候产生的影响。世界上上一次超级火山爆发发生在苏门答腊北部的多巴，那是在74000年以前。谁也不知道它的强度有多大，但肯定大得吓人。格陵兰的冰核显示，多巴火山爆发以后，至少有长达6年的“火山冬天”，天知道之后又有多少个糟糕的生长期。据认为，那次爆发几乎将人类灭绝，使全球的人口减少到不足几千人。这意味着，那几千人是所有现代人的共同祖先，这也说明了我们为什么缺少基因的多样性。无论如何，有证据表明，在此后的两万年里，地球上的总人数从没有超过几千。不用说，从一次火山爆发中恢复过来要花很长的时间。