A mass or stream of melted minerals or stony matter which bursts or is thrown from the mouth or sides of a volcano, and is sometimes ejected in such quantities as to overwhelm cities. Catana, at the foot of Etna, has often been destroyed by it, and in 1783, a vast tract of land in Iceland was overspread by an eruption of lava from mount Hecla.

The same matter when cool and hardened.