Every few months, a volcanic eruption occurs on Earth, with lava flows and enormous plumes of volcanic ash.
These small eruptions might produce only ~0.01 cubic kilometers of ash, while large, rare ones can produce thousands.
Unlike the result of combustion, however, what we call volcanic ash isn’t ash at all.
Combustive ash is what’s left when carbon-based material burns in the presence of oxygen: calcium carbonate, potash, nitrogen, and minerals and oxides.
It has many practical and survival uses, and is easily washed away with water.
Instead, volcanic ash is made of rock, mineral, and glass fragments as small as 4 microns (μm) each.
As magma rises from beneath the Earth, the gases dissolved within it expand and escape, shattering solid rock and shredding magma fragments into the air.
These tiny, airborne rock and glass fragments then solidify, where they can be blown tens or even thousands of kilometers away.
Macroscopically, volcanic ash is hard, abrasive, corrosive, and does not dissolve in water.
Large eruptions can block the sun, cause acid rain and thunder/lighting, and even suffocate nearby residents.
Ashfall then poses its own hazards to buildings and the environment.
Proper clean-up and disposal is difficult, but essential.