mode of occurrence of lava that has issued from a volcano. Lava flows are characterized by great length (up to several dozen kilometers) with relatively small width and thickness. The length and thickness of the lava flow depend on the viscosity of the lava and the slope of the terrain. Flows of acidic lava are usually short (1–10 km) and thick (up to 25–30 m); basaltic flows are long (up to 60–80 km and more) and very thin.