Ignimbrite

Tuff/ignimbrite is formed by deposition, compaction, and cementation of volcanic ash and debris (pyroclasts) ejected from an explosive volcanic eruption. The ejecta material is made up of fine ash, tephra, and large boulders bedrocks. Ejecta materials near the vent contain large blocks of rocks cemented in fine ash. Further away from the vent, the ejecta contains small clasts (lapilli) to a very fine ash. The thickness and coverage of the deposits depend on the prevailing wind direction during the eruption.