A volcanic bomb or lava bomb is a mass of partially molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption.
Because volcanic bombs cool after they leave the volcano, they are extrusive igneous rocks.
Volcanic bombs can be thrown many kilometres from an erupting vent, and often acquire aerodynamic shapes during their flight.
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.
Bombs are named according to their shape, which is determined by the fluidity of the magma from which they are formed.