What is the largest type of tephra?

Tephra, rock fragments ejected from a volcano during an eruption, are called blocks and bombs when larger than 64 millimeters in diameter. Because of their size, blocks and bombs fall close to their volcanic source.

Tephra are composed of pumice, glass, mineral crystals and different types of shattered rock. Volcanic eruptions blast tephra of different sizes, with the largest sizes ejecting from the volcano within 30 minutes of the eruption. Larger particles, such as blocks and bombs, land close to the source, while the smallest particles, such as ash, can travel through the air for more than two years after an eruption.