What is volcanic ash?

Volcanic ash is often talked about on the news when a volcano erupts or threatens to blow itself up but what actually is it?

It might surprise you to know that the term ‘ash’ (when we’re talking about volcanoes) is actually used to describe the grain-size of material ejected by a volcano. ‘Ash’ refers to all volcanic material of <2mm.

Pyroclastic grain-size classification
Grain-size classification for volcanic material (Cas & Wright 1988)

Therefore ash can be made up of a range of different materials all less than 2mm, including: rock fragments, crystals and fresh volcanic glass (AKA pyroclasts)

Components of volcanic ash
Volcanic ash can contain rock fragments, crystals and fresh volcanic glass (called pyroclasts)

Find out more: The wonders of volcanic ash – an introduction

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