 These basaltic lava bombs were erupted by Mauna Kea Volcano, Hawaii. |
Bomb
Volcanic bombs are lava fragments that were ejected while viscous (partially molten) and larger than 64 mm in diameter. Many acquire rounded aerodynamic shapes during their travel through the air. Volcanic bombs include breadcrust bombs, ribbon bombs, spindle bombs (with twisted ends), spheroidal bombs, and "cow-dung" bombs. |
 This dacite breadcrust bomb (about 15 cm in diameter) was erupted from the lava dome at Mount St. Helens, Washington. |
Breadcrust Bomb A breadcrust bomb is a volcanic bomb with a cracked and checkered surface, sometimes resembling the surface of a loaf of bread. The cracks develop when the outer surface of a partially molten lava fragment cools to form a brittle surface and then subsequently cracks as the hot interior expands due to the continued growth of gas bubbles. |