What is volcanic ash?

[Johnny_L.A]

Is volcanic ash, ash – the product of combustion? Or is it very finely powdered rock?

[Dr.Lao]

Here ya go

Small jagged pieces of rocks, minerals, and volcanic glass the size of sand and silt (less than 2 millimeters (1/12 inch) in diameter) erupted by a volcano are called volcanic ash. Very small ash particles can be less than 0.001 millimeters (1/25,000th of an inch) across. Volcanic ash is not the product of combustion, like the soft fluffy material created by burning wood, leaves, or paper. Volcanic ash is hard, does not dissolve in water, is extremely abrasive and mildly corrosive, and conducts electricity when wet.

Volcanic ash is formed during explosive volcanic eruptions. Explosive eruptions occur when gases dissolved in molten rock (magma) expand and escape violently into the air, and also when water is heated by magma and abruptly flashes into steam. The force of the escaping gas violently shatters solid rocks. Expanding gas also shreds magma and blasts it into the air, where it solidifies into fragments of volcanic rock and glass. Once in the air, wind can blow the the tiny ash particles tens to thousands of kilometers away from the volcano.

[Johnny_L.A]

Thanks, Dr. Lao. That’s what I thought.

(Incidentally, I have a little “gum machine” capsule of Mt. Saint Helens ash that my dad got after the 1980 eruption.)

[Desmostylus]

@Johnny L.A.

Is volcanic ash, ash – the product of combustion? Or is it very finely powdered rock?

There’s no straight, simple answer to that.

Volcanic ash is very finely powdered rock, but the stuff that’s left over after burning say, a tree or a lump of coal is pretty much the same stuff. All ash is basically rock - oxides of silicon, calcium, magensium, etc.