lavaflow

A lavaflow is the movement of molten rock that travels downslope or away from an eruption, once it has erupted as lava onto the surface. Lava flows are a common form of effusive volcanic activity and can shape landscapes for years or decades after eruption.

Lava viscosity depends on chemical composition, temperature, and gas content. Mafic magmas, such as basalt, tend to be hotter and less viscous, producing flowing lava that can advance as smooth pahoehoe or rugged aa. Felsic magmas (rhyolite, andesite in high silica) are more viscous and often form thicker, slower-moving flows. Temperature ranges for erupting lava generally span roughly 700 to 1,200 degrees Celsius.

Pahoehoe lava develops a smooth, ropy surface as the outer crust cools and wrinkles. Aa lava forms jagged blocks as the cooled crust breaks up while the flow continues. Some flows become lava tubes; once the crust solidifies above a tunnel, lava can transport through a hollow conduit, allowing the flow to advance with limited surface cooling.

Lava flow rates vary from a few meters per hour to several tens of meters per hour and, in rapid eruptions, kilometers per day. Flows can bury vegetation, roads, and houses, redirect rivers, and create new landforms. Fresh flows entering the sea can cause violent steam explosions and release volcanic gases.

Notable examples include ongoing lava flows from Kilauea and Mauna Loa in Hawaii, eruptions at Mount Etna in Italy, and historical events such as the 1783–1784 Laki eruption in Iceland. Modern monitoring uses ground-based observations, aerial surveys, and satellite remote sensing to map flow-front advance and assess hazards.