A tower had broken the cap. It had broken it suddenly and totally, the way a firecracker might rupture a cheap tin can. Great rounded torrents of vengeful superheated steam were thrusting themselves into the upper air, like vast slow-motion fists. The dozens of rising cauliflower bubbles looked as hard and dense as white lumps of marble. And up at the top of their ascent—Alex had to crane his neck to see it—vapor was splashing at the bottom of the stratosphere.