New Scientist: Nuclear weapons testing in most countries is generally limited to computer models. A low-tech alternative for modeling underground explosions simply requires popping a balloon buried under loose dirt and filming it at high speed. Although Felipe Pacheco Vázquez of the Autonomous University of Puebla, Mexico, and his colleagues weren't specifically modeling nuclear explosions, they did just that. They found that the resulting explosion forms a dome of dirt that then bursts into a wild spray before falling back down. As the dirt collapses into the crater, the material meeting in the middle splashes back upward in a thin jet. Underground nuclear tests aren't the only explosions that behave that way. Volcanic calderas and explosive releases of methane and other natural gas bubbles have created similar craters.
