23 people were injured in Hawaii yesterday when a LAVA BOMB crashed through the roof of their tour boat. A lava bomb is a large rock tossed through the area in a volcanic explosion, according to the U.S. Geological Survey. In this case, the rock that slammed into the tour boat was the size of a basketball. Four people on the boat were taken to the hospital after the lava bomb struck the boat. Two of those passengers are in stable condition, but the third, a woman in her 20s, was listed in serious condition with a fractured femur.