Volcanic bomb

Lava bomb, thrown from the Kīlauea Volcano, Hawaii in 1983

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. 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 600 m (2,000 ft) from the vent. Volcanic bombs are a significant volcanic hazard, and can cause severe injuries and death to people in an eruption zone. 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 usually 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.

Gallery

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  "Fusiform" type volcanic bomb. Capelinhos Volcano, Faial Island, Azores
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  "Almond" type volcanic bomb found in the Cinder Cones region of the Mojave National Preserve, California
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  "Bread-crust" type volcanic bomb at Vulcania, Puy-de-Dôme, France
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  Lava bomb at Strohn, Rhineland-Palatinate, Germany, with a diameter of 5 meters and a mass of 120 tons. It was caused by a volcanic eruption in 8300 BC

Other websites

• USGS Volcano Hazards Program