is an unconsolidated sediment, the air fall material from a volcanic eruption.
Large boulders may be expelled, but most tephra is the fine ash produced by
volcanic eruptions. The word tephra is Greek for "ash".
Tephra is the unconsolidated ash and larger materials such as cinders.
If it is hot enough to consolidate (fuse) when it accumulates on the ground, the
resulting material is called tuff or pyroclastic rock.