What is the smallest size tephra?

The smallest kind of tephra is volcanic ash, which is smaller than 0.08 inch in diameter. Any kind of fragmentary material produced by a volcano is considered to be tephra.

Ash is capable of covering a much greater area than other types of volcanic debris due to its size and the wind easily dispersing it following injection into the atmosphere. Ash can obscure sunlight and greatly reduce visibility. It becomes slippery when introduced to water and poses transportation hazards, and its abrasive texture can damage structures and lead to mechanical issues. The inhalation of hot ash is responsible for many deaths during a volcanic eruption, either from burns or asphyxiation.