as it fell through the air. Cow pie bombs are formed when highly fluid magma falls from moderate height, so the bombs do not solidify before impact (they are still liquid when they strike the ground). They consequently flatten or splash and form irregular roundish discs, which resemble cow dung. Bread-crust bombs are formed if the outside of the lava bombs solidifies during their flight. They may develop cracked outer surfaces as the interiors continue to expand. Cored bombs are bombs that have rinds of lava enclosing a core of previously consolidated lava. The core consists of accessory fragments of an earlier eruption, accidental fragments of country rock (such as xenoliths) or, in rare cases, bits of lava formed earlier during the same eruption. References External links USGS Volcano Hazards Program Tephra Volcanic rocks