In geology, molten rock is called lava after it reaches Earth’s surface.
Before eruption, molten rock beneath the surface is called magma. Once it emerges through a vent or fissure, it is classified as lava and may flow across the ground, erupt underwater, or accumulate into volcanic deposits. Its temperature and viscosity depend on composition, dissolved gases, and crystal content.
Basaltic lava is relatively low in silica and commonly flows easily, while rhyolitic lava is richer in silica and tends to be much more viscous. Cooling lava can form igneous rocks such as basalt, andesite, or rhyolite.
Tephra refers to fragments thrown through the air during an eruption, while tuff is a rock formed from consolidated volcanic ash. Neither term is a synonym for lava.