Kīlauea lava fountaining episode tephra clast sizes

This annotated photograph shows the different size categories of tephra associated with recent lava fountaining episodes at the summit of Kīlauea. The inset photo on the bottom left shows the vesicular (bubble-rich) texture of most of these clasts. The smallest particles of tephra are volcanic ash, and they are smaller than 1/16 of an inch (2 mm). Tephra that is between 1/16 of an inch and 2 ½ inches (2–64 mm) in size is called lapilli. Any tephra larger than 2 ½ inches (64 mm) is called a bomb or a block, depending on whether it is fresh lava or older material. Lava fountains also create a special type of tephra; the long, thin strands of volcanic glass that make up Pele’s hair, which is hard to classify by size. USGS photo.