 What caused the avalanche of rocks in the cavern?
But, if they could not realize that the company's regime served the best interests of the planet, they would just have to suffer the consequences of their own ignorance. This walk was part of a regular routine of physical exercise that kept his body hard and resilient in spite of long hours spent in the laboratory. He was making that walk in precisely seven minutes, four and four-fifths seconds. The battering thunder continued persistently. He swore some more and grabbed a towel, wrapping it inadequately around him; it didn't quite meet astern. Pete Brent's joking words flashed back to him. Four police constables and a sergeant swarmed into the room, shoving him away from the door. "Wherethehell's who?" "Quit stallin', bud.
 Vibrations from the ships’ exhaust.
 An atomite bomb.  A chemical reaction with the ships’ exhaust.  The vibrations of the advancing police.  Vibrations from the ships’ exhaust.