When volcanoes erupt, a large amount of material from the Earth’s interior, including extraordinary amounts of noxious gases like sulfur dioxide, are released into the atmosphere. The ‘smoke’ you see isn’t from combustive ash, however; volcanic ash is fundamentally different. (European Geosciences Union)

‘Volcanic Ash’ Isn’t Actually Ash

Whatever you do, don’t try to wash it away with water.

Every few months, a volcanic eruption occurs on Earth, with lava flows and enormous plumes of volcanic ash.

In 2015, the Chilean volcano Calbuco erupted for the first time in 42 years. Although the sight of volcanic lightning may be beautiful, the eruption itself causes significant damage and widespread devastation. (Jose Mancilla/LatinContent/Getty Images)

These small eruptions might produce only ~0.01 cubic kilometers of ash, while large, rare ones can produce thousands.

Scientists studying the ash from a recent eruption of Ol Doinyo Lengai volcano in Tanzania. This ash will not wash away during the next rainfall like combustive ash would. (public domain)

Unlike the result of combustion, however, what we call volcanic ash isn’t ash at all.

An ash particle imaged with an electron microscope from the Mt. St. Helens eruption of 1980. Volcanic ash has fundamentally different properties from normal, combustion-driven ash. (USGS / A.M. Sarna-Wojcicki)

Combustive ash is what’s left when carbon-based material burns in the presence of oxygen: calcium carbonate, potash, nitrogen, and minerals and oxides.

A wildfire as seen from near Stevenson Wash., across the Columbia River, burning in the Columbia River Gorge above the Bonneville Dam near Cascade Locks, Oregon. Although this type of disaster can have devastating effects, the ash produced is easily cleaned up and washed away, unlike volcanic ash. (Tristan Fortsch/KATU-TV via AP)