Teachers Guide to Stratovolcanoes of the World
Eruption Feature

Crater Peak, Alaska USA:
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Volcanic bombs

Bombs are glowing clots of liquid lava larger than 64 mm (2.5 in) in average diameter. Because the clots are soft when ejected from the vent, their shapes can be modified during flight. The bombs may start out as long irregular strings or as discrete clots of liquid. The strings commonly break up into short segments during flight. Cylindrical or ribbon bombs are segments that fall to the ground intact. Ribbon bombs are often twisted during flight. The thicker portions of the ribbons may separate from the rest during flight be pulled into spheres, forming ball-shaped (spherical) bombs. Other bombs may be spindle-shaped or irregular in shape. Many have a crust a few centimeters thick that looks much like that of a loaf of French bread. Some are flattened on one end, apparently on impact, indicating the bomb was not completely hardened. Because volcanic bombs cool very rapidly, usually during flight, they are often glassy in texture.

In the 1992 eruption of Crater Peak on Mt. Spurr, large volcanic bombs traveled up to 4 km (2.4 mi) from the crater. The size of these blocks and bombs ranged from 10 cm (4 in) up to 2 m (6.6 ft). Bombs littered the crater area and sides of the volcano.