Volcanic ash

Volcanic ash consists of rock, mineral, and volcanic-glass fragments smaller than 2 millimeters, blasted into the air during explosive eruptions. It can travel far downwind and abrade, contaminate, or burden surfaces.

Explosive eruption: A volcanic eruption that fragments magma and ejects gas, ash, and larger material. Rapid gas expansion shatters magma into the fine fragments that make up ash.
Volcanic ash hazard to aviation: The risk that airborne volcanic ash poses to aircraft and flight operations. Ash can melt inside jet engines and damage aircraft surfaces.
1912 eruption of Novarupta: A major 1912 Alaskan eruption that deposited thick ash and formed the Valley of Ten Thousand Smokes. Its deposits illustrate the scale and persistence of ash from a large explosive eruption.
Volcanic bomb: A volcanic fragment larger than 64 millimeters that solidifies after being ejected while molten. Unlike ash, bombs are large clasts that fall close to the vent.
Volcanic plume: A rising column of hot gas, ash, and rock fragments above an eruption vent. It carries ash upward before winds disperse it downwind.
Volcanic ashfall: The deposition of airborne volcanic ash onto the ground and built surfaces. Accumulating ash can overload roofs, disrupt transport, and contaminate water.
1980 eruption of Mount St. Helens: The 1980 explosive eruption of Mount St. Helens in Washington State. Its ash cloud spread across the United States and disrupted transport and daily life.
Lapilli: Loose volcanic fragments between 2 and 64 millimeters in diameter. Lapilli are larger than ash and generally settle nearer the eruption source.
Tephra: All fragmented material ejected by a volcano, regardless of particle size or composition. Ash is the fine-grained fraction of this broader category of erupted debris.
Volcanic ash and health: The effects of volcanic ash exposure on human health, especially the respiratory system and eyes. Fine particles can irritate airways and worsen existing respiratory conditions.

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