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These are volcanoes so explosive that they burst open in a single mighty rupture, leaving behind a vast subsided pit, the caldera (from a Latin word for cauldron). Yellowstone obviously was of this second type, but Christiansen couldn't find the caldera anywhere.
这种火山的威力如此之大，它们一下子破土而出，留下一个沉降式大坑，即破火山口（源自拉丁语，意思是大锅）。黄石火山显然属于第二种，但克里斯琴森哪里也找不到那个破火山口。
By coincidence just at this time NASA decided to test some new high-altitude cameras by taking photographs of Yellowstone, copies of which some thoughtful official passed on to the park authorities on the assumption that they might make a nice blow-up for one of the visitors' centers. As soon as Christiansen saw the photos he realized why he had failed to spot the caldera: virtually the whole park—2.2 million acres—was caldera. The explosion had left a crater more than forty miles across—much too huge to be perceived from anywhere at ground level. At some time in the past Yellowstone must have blown up with a violence far beyond the scale of anything known to humans.
恰好在这个时候，美国国家航空和航天局决定拍摄黄石公园的照片，测试一下某些新型的高空照相机。一位考虑周到的官员把其中的有些照片交给了公园当局，认为它们可以挂在某个游客中心。克里斯琴森一看到这些照片，马上意识到他没有找到破火山口的原因：实际上，整个公园——9000平方公里——就是破火山口。火山爆发留下了一个直径将近65公里的大坑——大得从地面上的任何角度都看不明白。过去某个时刻，黄石公园可能被炸得七零八落，威力之大远远超过了人类已知的任何等级。
Yellowstone, it turns out, is a supervolcano. It sits on top of an enormous hot spot, a reservoir of molten rock that rises from at least 125 miles down in the Earth. The heat from the hot spot is what powers all of Yellowstone's vents, geysers, hot springs, and popping mud pots. Beneath the surface is a magma chamber that is about forty-five miles across—roughly the same dimensions as the park—and about eight miles thick at its thickest point.
结果发现，黄石公园是一座超级火山。它坐落在一个巨大的热点——一个熔岩储藏所——之上。这个储藏所下达地球至少200公里深处，上至接近地面的地方，形成了一根所谓的超级热柱。热点的热量为黄石公园里所有的喷气口、间歇泉、温泉和冒泡的泥坑提供了动力。地面以下是个岩浆房，直径约为72公里——大致相当于公园的大小，最厚的地方达13公里左右。
