Volcanic bomb

A volcanic bomb or lava bomb is a mass of molten rock larger than 64 mm (2.5 inches) in diameter. It forms when a volcano throws viscous pieces of lava during a volcanic eruption. They cool into solid objects before they reach the ground. However, they are still very hot when they reach the ground, because they are still partly molten inside. Because volcanic bombs cool after they leave the volcano, they are extrusive igneous rocks. Volcanic bombs can be thrown many kilometers from an erupting fissure vent. They often get aerodynamic shapes during their flight. Lava bombs can be extremely large; the 1935 eruption of Mount Asama in Japan expelled bombs measuring 5–6 m (16-20 ft) in diameter up to from the vent. Volcanic bombs are a significant volcanic hazard, and can cause severe injuries and death to people in an eruption zone. One such incident occurred at Galeras volcano in Colombia in 1993; six people near the summit were killed and several seriously injured by lava bombs when the volcano erupted unexpectedly. On July 16, 2018, 23 people were injured on a tour boat near the Kilauea volcano as a result of a basketball-sized lava bomb from the 2018 lower Puna eruption.
Volcanic bombs are known to occasionally explode from internal gas pressure as they cool, but in most cases, most of the damage they cause is when they hit. As they are still hot when they land, they often cause a fire to start. Bomb explosions are most often observed in "bread-crust" type bombs.