Volcanic ash

Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions,United States Geological Survey. Tephra: Volcanic Rock and Glass Fragments. Retrieved on 2008-01-23. less than in diameter.
== How it is made ==
There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact with water causing phreatomagmatic eruptions and ejection of entrained particles during steam eruptions causing phreatic eruptionsHeiken, G. & Wohletz, K. 1985. Volcanic Ash. University of California Press, Berkeley.. The violent nature of volcanic eruptions involving steam results in the magma and solid rock surrounding the vent being torn into particles of clay to sand size.
Category:Volcanology