Volcanic ash is a mixture of rock, mineral, and glass particles expelled from a volcano during a volcanic eruption. The particles are very small—less than 2 millimeters in diameter. They tend to be pitted and full of holes, which gives them a low density. Along with water vapor and other hot gases, volcanic ash is part of the dark ash column that rises above a volcano when it erupts.

Due to their tiny size and low density, the particles that make up volcanic ash can travel long distances, carried by winds. When an ash column is moved about by wind, it is called an ash plume. Eventually the ash in the sky falls to the ground. It may create a thick layer of dust-like material on surfaces for miles around the original eruption.

Unlike the ash produced by burning wood and other organic materials, volcanic ash can be dangerous. Its particles are very hard and usually have jagged edges. As a result, it can cause eye, nose, and lung irritation, as well as breathing problems. While in the air, ash can cause problems for jet engines, forcing airlines to cancel flights through the affected area. An ashfall that leaves a thick layer of ash may cause roofs to collapse, clog gutters, and interfere with air conditioning units. Animals in an area coated by volcanic ash may have difficulty finding food, as the plants in the region may be covered in ash. Ash can also contaminate water supplies.

Volcanic Ash

Removing volcanic ash can be a difficult and laborious process. Here, two Icelanders shovel volcanic ash from a hillside in Vestmannaeyjar, a volcanic archipelago off the southwest coast of Iceland. 

ash cone

hill formed by ash falling from a volcanic eruption. Also known as a tuff cone.


number of things of one kind in a given area.


release of material from an opening in the Earth's crust.


having an uneven edge.


inorganic material that has a characteristic chemical composition and specific crystal structure.


fragments of lava less than 2 millimeters across.

volcanic glass

hard, brittle substance produced by lava cooling very quickly.